Analytical Chemistry Set AJJ
electroosmotic flow
'drag' of analyte because of friction
classical methods
'wet' gravimetric titrimetric complexometric and redox wet bench
wt%
(mass of analyte/mass of total solution of sample)*100
z score
(x- xavg)/s
molecular spin
*2(total electron spin) +1 *each electron spin is 1/2 because if these cancel it should equal 1 -they cancel each other out if arrows are opposite
Real rules for sig. figs.
- 1st digit of the absolute uncertainty is the last digit in the answer, or the last significant figure
Parameters that determine the effectiveness of separation include: Operational:(3) Column Parameters: (4)
- Column temperature - isothermal/gradient - Carrier gas velocity/flow rate - Amount of sample injected - Length - Internal diameter - Film thickness - Stationary phases composition
Formal Concentration
- F -rarely used, equivalent to molarity of initial species that in solution becomes something else
Line notation
- I = signals a phase boundary *occurs between two species - II = signals the salt bridge -the electrodes are shown at the extreme left (anode) and right (cathode) sides of the line format *typically these will be solids -the half-cell potentials tell us which is the anode and which is the cathode
Random Error (indeterminate error)
- always present - cannot be corrected - equal chance of being + or - - can be reduced by increasing number of trials/measurements
Linear Range
- analyte concentration. range over which the response is proportional to concentration. in calibration curve
systematic error (Determinate error)
- are repeatable -ex: incorrect standard, solution. concentration. wrong pH buf used to calibrate pH meter interference from component in sample lack of adequate selectivity - should always be able to detect and correct
Gravimetric Analysis
- chemical analysis based on weighing a final product
Dynamic Range
- concentration. range over which there is a measurable response to analyte in calibration curve
Pipetttes
- deliver known volumes of liquid - more accurate -two types 1) transfer pipettes - calibrated to deliver one fixed volume 2) measuring pipettes -like burets
Experimental Error
- difference between a measurement (result) and its 'true' (accurate) value -not always caused by mistakes -associated with every measurement
Using volumetric flasks
- dissolve desired mass of reagent in the flask by swirling with less than final volume of liquid - add more liquid and swirl again - adjust the final volume with as much well-mixed liquid as possible -fill to the mark on the neck of the flask so that you minimize the change in the last liquid that is added - after adjusting to the correct level, hold cap firmly in place and invert the flask about 10 times to complete mixing -tolerances get larger as volumes are increased
precipitate properties
- easily filtered and washed free of contaminants -sufficiently low solubility that no loss of analyte occurs when washed -unreactive with atmosphere -known chemical composition after heated
Accuracy
- how close to 'true' value
Arithmetic operations of measurements
- if uncertainties are not present with the measurements, follow rules of sig. figs -if uncertainties are present with the measurements 1) do the calculation with the central values first 2) calculate the propagation of uncertainty 3) round the answer so that its significant figure at the the lowest place matches the place of sig. fig. of the uncertainty
Goals of Analytical
- large sample sizes -statistics -precise & accurate measurements
Dissociation constants give information on fate of chemicals in:
- living organisms (sorption, distribution, metabolism and excretion) e.g. highly ionised drug/toxin cannot cross lipid membranes as opposed to unionised drug/toxin - environment (sorption, distribution, bioaccumulation)
Mass per unit volume
- mg/L -mg/dL -ug/mL
Never trust a Pipet
- micropipettes can have gross errors - as internal parts wear out, both precision and accuracy can decline by an order of magnitude
Burets
- precisely manufactured glass tube with graduations - measure the volume of liquid through a stopcock -different classes --> class A: most accurate -read meniscus at eye-level -->parallax error: not read at eye level
Confidence Intervals (CI)
- range of values within which there is a specified probability of finding the population mean --> the pop. mean is likely to lie within a certain distance from the measured mean
analytical balance
- reads from .001 mg -200 g
RSD
- relative standard deviation - = standard deviation /mean
Calibration curves
- show response of an analytical method to known quantities of an analyte
Uncertainty
- shows range of possible values that the 'true' value might reasonably be expected to have. Every measurement has some uncertainty
Blank solution.
- solution. containing all reagents and solvents used in the analysis but no analyte is added - blank value is subtracted from measured values of standards prior to constructing the calibration curve
Standard solution.
- solutions containing known concentration of analyte
Student's t-Test
- statistical tool used to express confidence intervals and compare results from different experiments Three cases 1) Comparing a measured result with a 'known' value 2-1) comparing replicate measurements with similar standard deviation 2-2) comparing replicate measurements with significantly different standard deviation 3) comparing differences of individual measurements of different samples obtained using different methods
Stoichiometry
- the quantitative relationship between constituents and/or chemicals --> calculations of quantities of substances involved in a chemical rxn -determine starting materials -calculate product amounts -to convert between different substances
Relative Uncertainty
- the uncertainty in a quantity diveded by the magnitude of the quantity. - % releative uncertainty = uncertainty in quantity/magnitude of quantity x 100 -use larger volumes to decrease the %relative uncertainty
For analytical method that requires several steps
- there will be random errors along with way associated with each step -the total error will be more than just the instrument reading step
Uncertainty
- uncertainty shows a range of possible values that the true value might reasonable be expected to have - caused by both systematic & random error -can be propagated through an experiment
Internal standards
- use when calibration curve is unreliable - add a known amount of a substance different from analyte added to unknown - Respond proportionally -useful for analysis in which the quantity of sample varies by a few % - different than calibration curve - Useful when ample loss can occur during sample prep steps prior to analysis
Combination methods
- used to achieve analytical accuracy
Volumetric Glassware
- volumetric glassware is colibrated by weighing water contained in or delivered by the vessel - in the most careful work, solution concentrations and volumes of vessels should be corrected for changes in temp -contains a particular vol. of solution -bottom of meniscus should be at the line
Beer's law
-1 molecule will absorb 1 photon and 1 photon can only be absorbed by 1 molecule -E (molar absorbtivity constant) per bond is = hc/ wavelength *no control over E, constant
Procedure that produces a detection limit greater than blank
-1) estimate detection limit, prepare samples w/ concentration. 1-5 times greater than detection limit 2) measure teh signal from n replicate samples 3) calc. standard deviation 4) measure the signal from n blanks (no analyte) and find mean of Yblanks 5) find minimum detectable signal 6) corrected signal is proportional to the sample concentration.
Carbon isotopes
-13C is only 1.1% of 12C abundance so this is MUCH LESS abundant than 12C -not like Cl or BR isotopes, one has MUCH MORE abundance than other isotopes
***Strong acid
-6 common strong acids 1. HCl, hydrochloric acid 2. HBr, hydrogen bromide 3. HI, hydrogen iodide 4. H2SO4, sulfuric acid -- notes that this is a diprotic acid *only the first proton ionization goes to completion and need to look at equil. for the second one 5. HNO3, nitric acid 6. HClO4, perchloric acid *also note that HF is not a strong acid *Ka >> 1
Why do atomic lines have width? -- Doppler effect
-Doppler effect means atoms moving towards or away from the light source "see" a different wavelength than a stationary atom *energy absorbed remains the same *moving towards the light source, atoms "see" smaller wavelength than the actual wavelength (aka absorbs 532.5nm, but sees 532.5 as 532.4 nm -- no absorption change though) -the faster the atoms are moving, the bigger effect they have -and the higher the temp, the greater the doppler broadening is
Ecell
-Ecell = Ecathode - Eanode *can do this same reaction with SRP -the E with the degree sign signals standard conditions -by convention, E^(standard) = E(standard cathode) - E(standard SHE) = E^(standard cathode)
for MS problems
-If H+ and OH- present as MS in a reaction, limiting reagent problem, using a mole table -If only weak species present: WA uses ICE table with Ka, WB uses ICE table with Kb, and WA and WB uses H-H equation
When using assumptions in solubility problems
-If the assumption is true, it does not create a contradiciton -If the assumption is false, it does create a contradiction -You need to test whethere or not the assumption was correct at the end of a problem -Ex. (x)(2x + 0.030)^2 = 7.9 * 10^-9 *assume that 2x << 0.030 so can eliminate 2x from the problem and just solve (x)(0.030)^2 = 7.9 * 10^-9 *once you solve for x, just multiply it by 2 and see if it is in fact << 0.030 and if it is, than can leave it this way and if not, redo the problem
pka and pH relationship
-If the pH is lower than the pKa, then the compound will be protonated *pka > pH, protonate -If the pH is higher than the pKa, then the compound will be deprotonated *pH > pka, deprotonate -a further consideration is the charge on the compound *acids are neutral when protonated and negatively charged (ionized) when deprotonated
Overloading a column
-If you overload a column with too much solute/mixture or at a too high concentration of that mixture, the solute will not be able to interact with MP particles
Galvanic cell (aka voltaic)
-In this type of cell, a spontaneous chemical reaction generates electricity *aka a spontaneous redox reaction generates electricity (a flow of electrons) -physically sperate oxidized and reduced species -anions flow toward the anode and cations flow toward cathode
Partition chromatography
-Involves a thin liquid stationary phase coated on the surface of a solid support -Solute partitions between stationary and mobile phase to different degrees
Indicator
-Is a compound with a physical property (usually color) that changes abruptly when the titration is complete
Titration
-Is a procedure in which increments of a known reagent -- the titrant -- are added to analyte until the reaction between the titration and the analyte is complete -The analyte has an unknown concentration -Common types of titrations: 1. acid-base 2. oxidation-reduction 3. complex formation 4. precipitiation reactions -In all titration reactions, we need to know when the analyte is completely used up -Titration reactions must be quick and reach completion (which means a high K, strong forward reaction)
buffer
-Is a solution that RESISTS changes in pH when a SA or SB is added -Typically consists of a WA and WB soln. -Contains species that can react with H+ and OH- and turn them into something else *WA and WB conjugate pair normally -The buffering region is about 1 pH unit on either side of the pKa of the conjugate acid -a buffer resists chnages in pH because the added acid or base is consumed by the buffer *as the buffer is used up, it becomes less resistant to changes in pH -pH of a buffer does NOT change very much when a limited amount of strong acid or strong base is added because it is consumed by B or BH+ -FOR BUFFER PROBLEMS, CAN USE MOLES FOR CALCULATIONS INSTEAD OF [ ]'s
temperature stability
-Is most important in atomic EMISSION (AES) -ICP is the best atomizer for AES because most stable temp. -the smaller number of atoms being probed, the bigger temperature fluctuations matter
Equivalence point
-Is reached when the quantity of titrant added is the exact amount needed for stiochiometric reaction with the analyte *where all the analyte is used up and there is no excess titrant -What we actually measure as the equiv. point is the end point = when one of the detection methods signals the end of titration *sudden change of physical property of the solution (normally color change) -Titration error = difference between equivalence point and end point
***Solubility product, Ksp***
-Ksp is the equilibrium constant for the reaction in which a solid SALT (an ionic compound) dissolves to give its consistuent ions in solution -omit pure solids from equilibrium constants -this problems are when we start using an ICE table -solubility of a salt: concentration of a salt in a saturated solution -Ksp rxn means that I am taking one unit of a solid and dissolving it into its complete ions in aqueous solution *HIGHER Ksp means that the salt is more easily dissolvable -the Ksp expression for a salt is the product of the concentrations of the ions, with each concentration raised to a power equal to the coefficient of that ion in the balanced equation for the solubility equilibrium
some terminology when it comes to ETDA titrations
-Kx (Kfx) = means adding a single ligand -Beta x = means adding multiple ligands at one time *for EDTA we use Kf1 (Kf)
-Lewis acids and bases
-Lewis acid: electron pair acceptor -Lewis base: electron donor
Weighing by difference
-Necessary for hydroscopic reagents -sample to be used is dried in a weighing bottle -set initial mass of weighing bottle to zero -quickly deliver the dry reagent from the bottle to the receiver -cap and reweigh bottle -the negative reading on the balance is the mass of the reagent delivered from bottle
Steps in undertaking an analytical toxicological investigation
-Pre-analytical Obtain details of suspected poisoning episode Obtain the patient's medical and occupational history Decide the priorities for the analysis -Analytical - perform the agreed analysis -Post-analytical - interpret the results
Titrants used-- Primary Standards
-Primary Standard = is a reagent that is pure enough to weigh out and directly use directly to provide a known number of moles -Common primary standards: 1. sodium carbonate, Na2CO3 (weak base) 2. TRIS or THAM, (CH2OH)3CNH2 (weak base) 3. KHP, KHC8H4O4 (weak acid) 4. potassium hydrogen diiodate, KH(IO3)2 (weak acid) 5. potassium dichromate, K2Cr2O7 (redox standard) 6. AgNO3 -Primary standard should be 99% pure or better and not contmainated with any other species *cannot decompose and should be stable when dried or heated because drying is required to remove traces of water from the atomosphere *most things are not avaiable as primary standard so use secondary standards -NaOH and KOH are NOT PRIMARY STANDARDS
SA and SB reactions
-SA and SB are strong enough to force reaction to completion to need to have a relatively large K vaule to be able to do this *driving forward reaction -the pH of a buffer is nearly independent of dillution
SA/SB Titration
-SA is the analyte -SB is the titrant *the SA is being titrated by the SB -acid/base titration = transfer 1 H+ *so 1:1 stoichiometry *equiv. point: mol acid = mol base -the MS effecting this reaction and pH are H+ and OH- -pH = 7.00 at equiv. point before equiv. pnt., xs SA so pH < 7 after EP, xs SB so pH > 7 -know that the pH at equiv. point is 7 here and after equiv. point, more basic, and before equiv. point more acidic
Titrants used-- Secondary Standards
-Secondary standard: a solution that has approximately the desired concentration is used to tirtate a weighed, primary standard *a solution that is titrated with a primary standard *from the volume of the titrant required to to react with the primary standard, we can calculate the concentration of the titrant *the titrant is the standard solution -Standardization: the process of titrating a standard to determine the concentration of titrant
Sig figs and certainties
-THE FIRST UNCERTAIN FIGURE IS THE LAST SIGNIFCANT FIGURE -even if that makes the result break the sig fig rules -absolute error only have 1 sig fig and its position related to the decimal point dictates the last sig fig in the answer -HOWEVER, when the first digit in the absolute uncert. is 1, we can have 2 sig figs in the absol uncertainty
WA/SB titration
-WA is the analyte (unknown) and SB is the titrant (known) -in a WA problem, the pH is normally more than 7 at equiv. point because it takes so long for analyte to react fully with SB -the pH = pka where the buffer line is (flat line section) -rapid increase of pH to start with and then smooths out
Indicator with acids and bases
-WA/WB conjugate pair where acid and base form present in different colors -if we have a 10 fold excess of one form of WA or WB, can see just that one indicator color -inidcators change color over the pH range -choose this based off which Pka, ind is as close to equiv. point as possible *change color over pH range of +/- 1.00
WB/SA titration
-WB is the analyze and SA is the titrant -rapid fall off of pH to start but rate slows down -this can be a buffer problem -equiv. point is most likely less than 7 -xs SA after the equiv. point
Practicing assigning oxidation numbers in a redox reaction
-When something gets oxidized, its oxidation number increases (gets more positive or less negative) -When something gets reduced, its oxidation number decreases (gets more negative or less positive)
Back titration
-a KNOWN EXCESS of standard reagent is added to the analyte (the excess occurs beyond the equivalence point) -then a second standard reagent is used to titrate the excess of the first reagent (you are determining the amount of excess there is from the first reaction) -back titrations are useful when the end point of the back titration is clearer than the end point of the direct titration of when an excess of the first reagent is required for complete reaction with analyte
Electrolysis
-a chemical reaction in which we apply a voltage to drive a redox reaction that would not otherwise occur *aka applying a current to drive a non-spontaneous rxn -outside power source -electroactive species: is one that can be oxidized or reduced at an electrode
Electrodes
-a device to conduct electrons into or out of the chemicals involved in a redox reaction *aka use electrodes to shuttle electrons in and out of solution -if the electrode is part of the reaction = active electrode -if the electrode is not part of the reaction itself = passive electrode
***EDTA back titration
-a known excess of EDTA is added to analyte -EDTA is then titrated with a standard solution of metal ion -back titration is necessary if analyte percipitates in the absence of EDTA, if the analyte reacts too slowly with EDTA, OR if the analyte blocks the inhibitor -essentially the excess EDTA is the analyte and the metal ion is the titrant (so do not use metal that displaces analyte from EDTA) -an EDTA back titration can prevent precipitation of an analyte Steps: 1. metal ion is your analyte, add excess EDTA 2. the total EDTA = reacts metal ion and excess EDTA 3. now treat excess EDTA as the analyte and use the metal ion as the titrant
masking agent
-a masking agent protects some component of a mixture from reaction with EDTA -a reagent added to prevent reaction of some metal ion with EDTA -demasking: refers to the release of a metal ion from a masking agent -Cyanide is an example of a good masking agent *can form complexes with Cd2+, Zn2+, Hg2+, Co2+, Cu2+, Ag+, Ni2+, Pd2+, Pt2+, Fe2+, and Fe3+, BUT NOT WITH Mg2+, Ca2+, Mn2+, or Pb2+ *so, when CN- is added to a solution containing Cd2+ and Pb2+, the CN- will react with the Cd2+ to form a complex while the Pb2+ will react with EDTA -Fluoride can mask Al3+, Fe3+, Ti4+, and Be2+
Neutralization reaction
-a neutralization reaction is when an acid and a base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water -the neutralization of a strong acid and strong base has a pH equal to 7
Acidic vs. Basic
-a solution is acidic if [H+] > [OH-], where the pH is below 7 -a solution is basic if [OH-] > [H+], where the pH is above 7 -if the pH = 7, the solution is said to be neutral -- blood pH ~ 7.4
chromatography terminology
-aDsorption: sticking to a solid surface -mobile phase: solvent mobing through a column (gas or liquid) *in gas chrom. = MP is a gas *in liquid chrom. = MP is a liquid -stationary phase: the substance that stays fixed inside the column is usually a solid or a liquid and is covalently bonded to solid particles or to the inside wall of of a hollow capillar column -eluent: fluid that is entering the column -eluate: fluid exiting the column -eultion: moving through the column (process or l or g passing through the column) -chrom. can be classified by the type of interaction of the solute with the stationary phase
Systematic error
-also called a determinate error -is repeatable if you make the measurement over again in the same way -in theory, a systematic error can be discovered and corrected if you catch it -error within the system itself -- it could be an error in a buret or pH meter -this type of error skews the data in the same direction by ~ the same amount every time/ every measurement -could be relative or absolute error -can normally eliminate systematic error through the calibration of your instruments
Random error
-also called indeterminate error -this type of error skews from the true value in either direction, different amounts each time -it is hard to determine the source of this error and hard to correct it -- random error cannot be eliminated -mulitple trials of the same experiment could help lessen random error though -could be different people reading the same instrument
Molecular exclusion chromatography
-also called size exclusion, gel filtration or gel permeation chromatography -seperates molecules by size, with the larger molecules passing through the fastest -no attractive interactions between SP and solutes -SP has pores small enough for only small molecules to pass through, excludes the large molecules from passing through -large molecules stream through SP without entering channels/pores -small molecules take longer to pass through column because enter pores and therefore flow through a larger volume
multidentate ligand
-also known as a chelating ligand -meaning the ligand essentially engulfs the metal ion much like a lobster would grab an object
Conditional formation constant
-also known as the effective formation constant -this describes the formation of the metal-EDTA complex at any particular pH -we see that metal-EDTA complexes are less stable at lower pHs
Coulometry
-analysis by electron counting *aka electrons participating in a chemical reaction are counted to learn how much analyte reacted -using a CONSTANT current for a MEASURED amount of time ---> total coulmbs needed ---> moles of electrons transferred ---> moles of analyte (NEED TO USE ALL ANALYTE)
EDTA direct titration
-analyte is titrated with standard EDTA -an auxilary complexing agent may be required to maintain the metal ion in solution in absence of EDTA -analyte: metal ion titrant: EDTA -add titrant to anlyte solution until end point is observed
indirect titration of anions
-anions that precipitate metal ions can be analyzed with EDTA by indirect titration -analyte = nonmetal complex -you react analyte with a metal ion to form a known complex, and then redissolve collected solid and do direct titration on metal ion -precipitate is then reacted with excess EDTA to bring the metal ion back into solution -the excess EDTA is titrated with Mg2+ solution
Voltaic cell basics
-anode: where the oxidation occurs *on the left side of galvanic cell -cathode: where the reduction occurs *on the right side of the galvanic cell -electrons always move towards more positive electric potential -can normally see all half-reactions as reductions
Pressure broadening (one of the main sources of line broadening)
-as atoms collide, electron cloud deforms -the energy of atomic orbitals change (delta E b/t orbitals changes) -higher pressure induces more broadening (PV = nRT)
Equilibrium constant, K
-at equilibrium, both the forward and reverse rates of reaction are equal -the ratio in the equation can be more accurately described as a ratio of activities rather than a ratio of concentrations -the reaction is "favored" whenever K > 1, K being the eqilibrium coefficient -the formula is a ratio of products over reactants -concentrations of pure solids (s) or pure liquids (l) are to be OMITTED from the eqilibrium formula (because they are in unity) -all concentrations used in the formula should be expressed in M (moles per L) -if two reactions are added, the new K is the product of the original two K's (the two reactions or just added and therefore just multiply their K's together) -reversed reaction: 1/K
Ligand
-atom or group of atoms that bind to a metal ion
auxiliary complexing agent and when it is used
-between pH 9-12, it may be necessary to use an auxilary complexing agent which forms a weak complex with the metal ion and keeps it in solution -the auxilary complexing agent is displaced by EDTA during titration -some examples of these complexing agents include ammonia, tartrate, citrate, trethanolamine, etc. -these agents prevent metal ions from percitpating in the absence of EDTA
crystalline suspension
-bigger particles, tenths of a millimiter or greater -tend to settle spontaneously -easily filtered
EDTA as a chelating ligand
-binds to metal ions through two N atoms and 4 O atoms -metal ions are accepting electrons in this case and EDTA is donating electrons (so metal ion is the acid and EDTA is the base) -forms strong 1:1 complexes with most metal ions -refer to EDTA sometimes as Y4- = fully deprontated EDTA
atomic spectroscopy
-breaking down molecules to atoms and measuring absorption or emission of those atoms
Buffer titration problems
-can all be approached as a MS problem and then look to see if you need an ICE table or a mole table -mole table when you have H+ or OH- present in problem and ICE table when not
theoretical plates
-can imagine moving through the column as a series of regions of equillibration or plates -number of plates we use/calculate depends on the solute -if N = # of plates and H = plate height, then H = L / N, where L = column length *all plates in a column have the same height -But, if looking at different chrom. columns, the plates with wider heights have wider peaks While, the plates with the smaller heights have narrower peaks -the bigger resolution, the better seperation on the plates *resolution = telling two peaks apart quanitatively -the longer the solute spends on a column, the wider it will be
endpoint with EDTA
-can see the physical change (color change) once all metal ions are bound to the ligand
how to treat polyprotic acids
-can treat as fully protonated form of AA as monoprotic *use ICE table with Kas -and can treat full depronated form as monobasic *use ICE table with Kbs -ka1 is when loses first H and ka2 is when loses second H *lose one H from carboxlyic acid and one H from amino group -ka1 refers to the most acidic ion (which is on carboxyl group)
evaluating a spectrum
-cannot determine number of compounds just from the spectrum --spectra by itself cannot tell us much about the mixtures in the solution
Carboxylic acids and amines
-carboxylic acids *acetic acid is a good example of a carboxylic acid that is a weak acid *ammonium ions are good weak acids too **R3NH+ -amines *carboxylic anions (RCO2-) and amines (R3N) are good weak bases
preparative chromatography
-carried out on a large scale to isolate a significant quantity of one or more components of a mixture -purification of solutes -use a short and fat column that handles larger qualities of substance better but has worse resolution *may be expensive to buy and hard to operate
Kw
-changes with temperature -relationship between Ka and Kb, Ka * Kb = Kw *for a conjugate acid-base pair in aq. solution -Kw = 1.0 * 10^-14 at room temperature
Relative uncertainty
-compares absolute uncertainty with its associated measurement -relative uncertainty = absol. uncert. / mag. of measurement -ex. buret reading is 12.65 +/- 0.02 -- the relative uncert. is 0.02/12.65 = 0.0016
redox indicators
-compounds with different colors in oxidized vs. reduced form -to see mixture of the two forms as one color must have at least 10X excess of one of either the oxidized or the reduced form of the indicator -redox indicators change color over range E^(degree sign) +/- 0.05916/n -absolute value of [E^(standard analyte) - E^(standard titrant)] > 0.4 V to use the color changing indicator *redox indicator needs to be above 0.4 V to be of any use
analytical chromatography
-conducted on a small scale to separate, identify, and measure components of a mixture -uses a long thin column to obtain a good resolution -looking at what is in our mixture, what is present? 1. Qualitatively: identify compounds by retention times 2. Quanitatively: identify and quanitfy compounds *how much of each compound is present -small-scale analysis
Saturated solution
-contains all of the dissolved solid possible under given conditions *aka a solution that contains all solid capable of being dissolved*
Faraday constant
-coulombs / moles
base
-decreases the concentration of H3O+ in aq. solution (increases OH- in soluntion, hydroxide ion) -Bronsted/Lowry def: base is a proton acceptor, gains a proton *OH- would accept a proton to become H2O
micropipettes
-deliver volumes of 1-1000 uL
Sig figs in multiplication and division
-determine the number of sig figs in the answer based on the number that had the fewest number of sig figs in it
Indicator error
-difference between the observed end point (color change) and the true equivalence point
Electrical potential
-difference in electrical potential is a measure of the amount of wokr involved in transferring charge between two points -electrical potential is measured in volts, 1 V = J/C -potential difference = E -Work (J) = electrical charge (C) * electrical potential (V = J/C)
EDTA titration techniques
-direct -back -displacement -indirect
why are larger particles better for gravimetric work
-easy to filter -easy to wash free of impurities -purer than precipitates made up of fine particles
Coulomb
-electrical charge is measured in coulombs -equal to Amperes * seconds (Ampere is a measure of current)
Weak acids and bases
-equil. lies on the side of the weaker acid and weaker base -weak acid where K << 1, Ka and/or Kb << 1 -weaker acid is weaker than H3O+ -must consider equil. with these types of problems -weak acid, reactant side -weak acids: HA and BH+ -weak bases: A- and B
derivative graph
-equivalence point is point of max rate of change (in these types of graphs, highest curve when looking at y-axis height) -shows the change in slope of the titration curve as a function of the added volume of base -the first deriv. can also be referred to as "the slope," and the second deriv. can be referred to as "the slope of the slope" *end point is at the max slope for first deriv. *for the second derivative, the slope is 0 for the end point -the peaks in deriv. 1 and 2 match up (but look like opposites?)
gaussian distribution
-essentially just a normal, bell-shaped distribution -mean locates the center of the curve (the sample mean) -standard dev. measures the width of the curve (sample standard dev.) *the smaller the s, the more precise (reproducible) your results are, but greater precision does not always mean greater accuracy
phosphorescence
-excited state to ground state with photon emission on a long time scale (relatively) -absorbance is always from ground to excited state while emission could be from excited to ground state -the photons in the HOMO and LUMO diagram are the SAME direction for both arrows
fluorescence
-excited state to ground state with photon emission on a short scale -giving off light around the same time as absorbance of photons -absorbance is always from ground to excited state while emission could be from excited to ground state -the photons in the HOMO and LUMO diagram are OPPOSITE direction for both arrows
Ion exchange chromatography
-features ionic groups such as -SO3- or -N(CH3)3+ covalently added to the stationary solid phase (normally a resin, fir or pine needles) -MP is a liquid -solute ions are attached to stationary phase through electrostatic forces -ionic groups on surface of SP attact some solute groups more than others
spectrophotometric titration
-following a titration by absorbance -follwoing absorbance of the product would give the best results
dissociation constants explained
-for a solution with a very weak K1 and an even weaker K2, can make the assumption that it behaves like a monoprotic acid and does not lose both protons -so Ka = K1 ex. if K1= 4.7 10^-3 and K2 = 1.8 10^-10 -generally, a solution of diprotic acid behaves like a solution of monoprotic acid with Ka = K1
sig figs with logs and antilogs
-for logs and taking the antilog (ln), in the result, only the numbers/units after the decimal place are considered significant so you need to count the sig figs in the answer starting after the decimal place
Sig figs in addition and subtraction
-for numbers with exponents, express all numbers with the same exponent and alig all numbers with respect to their decimal points when setting up the problem -round off the answer according to the number of decimal places in the number with the fewest decmial places (sig. figs. go according to DECIMAL PLACES)
EDTA displacement titration
-for some metal ions, there is never a good indicator, but a displacement titration can still work -analyte is the metal ion, titrant is the metal-EDTA complex -analyte is treated with excess metal ion-EDTA complex to displace the metal ion, which is then later titrated with standard EDTA -so the second half of this is direct titration -requires that original metal-EDTA complex has a higher Kf than xs metal-EDTA complex -need a high K value for this reaction
***dominant form***
-form of acid or base present in highest concentration in soln. -when pH = pka, [base] = [acid] -if the pH > pka, the base is in the dominant form (deprotonated) -if the pka > pH, the acid is in dominant form (protonated)
EDTA
-four carboxylic protons pka1: 0.0 pka2: 1.5 pka3: 2.00 pka4: 2.69 -two amino protons pka5: 6.13 pka6: 10.37 @ low pH, H+ competes with Mn+ for EDTA @ high pH, OH- competes with EDTA for Mn+ *M(OH)n tends to be insoluble *at pH between 9-12 may need auxiliary complexing agent: can form with complex with metal ion and keep it in solution; prevent metal ions from forming percipitant in absence of EDTA
pH of SB in solution
-get [OH-] from the SB -if [OH-] > 10^-6, ignore [OH-] from water -if [OH-] < 10^-6, need to consider water when figuring out [OH-] concentration
pH in strong acid
-get the pH directly from H+ concentration
Potentiometry
-getting chemical information by measuring potential differences -using voltage measurements to extract chemical information
confidence interval
-given the sample mean, give a range where we expect the true population value to fall within *in class we use the 95% CI
***"best buffer"
-has equal concentrations of WA and WB and LARGE concentrations too -if do not have WA and WB, the concentration of the WA or WB has to be > than the SA or SB in the solution to make it an okay buffer -choose buffer where pH ~ pka (as close to each other as possible) -need to be careful, as T changes, pka changes
polyprotic acids
-have more than one acidic proton -- can play with more than one H on a particular species -amino acids are polyprotic -- can react with the Hs from the amino group or the Hs from the carboxyl group -zwitterion = contains both positive and negative charges
Reducing and oxidizing agents
-higher (more positive) E^(standard V) are better oxidizng agents *the more positive the E, the more energetically favorable the half-reaction is *bigger tendency to accept electrons = better oxidizing agent and bigger E value *some of the better oxidizing agents are F2 (g) and O3 (g) -lower (more negative) E^(standard) makes it a better reducing agent because most likely to give up electrons *Li(s) and K(s) are the best reducing agents (E(standard) ~ -3)
atomizer -- furnace (oven)
-higher temp than flame and higher sensitivity (less sample and less concentration required) Pros: -allow for the pre-concentrating of the sample -less sample needed so works for cases where you have a limited sample Cons: -poorer reproducitily -- "hot spots in furnance that can shift each time" -more stages to optimize, not as easy to use as flame
Fractional dissociation
-how many acid molecules have dissociated over the total acid molecules -as concentration increases, pH goes down and fract. diss. goes down -[H+] / [F of soln.] *for weak acids I think?
properties of light
-if a color is absorbed by a compound, than that is not the color we will see -the color we will see is the one opposite on the color wheel -- aka the light that will be visble to us is opposite the color wheel to the light that is absorbed -ROYGBV
closed shell molecules
-in the ground state, all the electrons are paired up -ground state -- labeled S0 because it is the singlet state
sources of systematic error
-instrumental -method -personal
Qsp
-it is the same as the solubility constant for a reaction in which a solid salt dissolves into its ions -EXCEPT this Qsp refers to NON-STANDARD conditions, where Ksp refers to standard conditions -same idea as the regular equilbrium constant and Q -in a purely saturated solution, Qsp = Ksp -percipitant starts when Qsp = Ksp -soluibility of a salt refers to mol/L of the solid salt that can be dissolved to give a saturated solution under standard conditions
nucleation
-large number of particles -small size particles -dominant in solutions with increasing relative supersaturation (colloidal solution)
pKa = Acids are most highly ionised at a "..." pH and bases at "..." logKow - "..." and is a measurement of "..." pKa is defined as the pH "..."
-logKa high low octanol water partition coefficient hydrophilicity/phobicity where chemical exists as 50% ionised and 50% unionised
p function
-log[x]
***Major species***
-look at major species in buffer reactions -defined as species with NON-ZERO concentrations in the INITIAL row of an ICE table -want to list major species for most reactions and ALWAYS react strongest acid with strongest base present -list of major species and their categories: 1. SA: H+ (with a garbage base present) 2. SB: OH- (with garbage acid) 3. WA: HA 4. WB: B 5. Ionic: anion, cation
reference electrode
-maintains a fixed (reference) potential -provides a constant half-cell potential to measure up against Ecell = Eindicator - Ereference -common reference electrodes: 1. silver-silver chloride electrode 2. calomel electrode (Hg2Cl2) *you know it is this type of electrode when the cell is saturated with KCl *saturated calomel electrode (SCE)
Adsorption chromatography
-makes use of different adsorption characteristics of solutes for the stationary phase -use a solid stationary phase and l or g mobile phase -solute is absorbed on the surface of the solid particules
Info that a mass spec gives you
-mass spec shows isotope patterning. not the average of molar masses -gives you the nominal mass = is the mass of the MOST abundant isotope -the mass unit in mass spec is the dalton and it gives you the mass of one proton or neutron * dalton (da) = 1/12 for 12C
dual beam spectrophotometer
-measures blank and sample at the same time -contains a rotating mirror of sorts
Mass spectroscopy
-measures the masses and abundance of ions in the gas phase -species must have a charge to show up in the mass spec -you are indentifying compounds by mass here -measure mass to charge ratio for these molecules: Mass / Z (charge) -before separation into mass spec, molecules must be converted into ions and measured through mass to charge ratio
How do we find the end point for EDTA titrations?
-metal ion indicator: ligand with different color depending if bound or unbound to metal ion -for an indicator to be useful, it must bind metal less strongly than EDTA does so that in the reaction the metal ion can react (bind) with EDTA and un-bind with the indicator *the indicator must be able to give up its metal ion to EDTA *if the metal does not freely dissociate from the indicator, the metal is said to "block" the indicator -- the Kf indicator > Kf EDTA-complex, the solution will not change colors -one mole of EDTA reacts with one mole of metal ion
What happens if you want to titrate a mixture of metal ions?
-metal ion indicators can indicate the presence and/or absence of free metal ions -If you have a mixture of Ca2+, Mg2+, and Fe2+, you can only see the color change (endpoint) when all of these metal ions are bound to EDTA in solution -you could use a masking agent here for some of these metal ions if you do not want all of them to bind to EDTA in solution
Metal ions and weak acids
-metal ions with a charge of 2+ or greater are WAs -Fe3+ is a weak acid
Types of ionization methods:
-methods to convert molecules into ions 1. Electron ionization: hit molecule with high energy electron, which knocks off an electron from that molecule -make the molecule have a (+)-charge now -this often forms have energy molecular ions -this can also cause fragmentation which is when some molecules appear in the mass spec and some do not *this can be good because can give us structural info about the compound 2. Chemical ionization -use reagent gas (often methane) and ionize by electron ionization -gaseous ions collide with molecules and the charges get transferred
metal ions and EDTA
-most metal ions have 6 binding sites to use -EDTA is the most common hexadentate ion -- 6 binding sites -- ligands are lewis bases and donate electron pairs (for binding/bonds?) -kx means adding a single ligand at once and betax means adding multiple ligands at one time
metal ion binding sites
-most metal ions have six binding sites -EDTA is hexadentate (meaning that it has six binding sites and can donate 6 electron pairs at one time)
Affinity chromatography
-most selective kind of chromatography. -employs specific interactions between one kind of solute molecule and a second molecule that is covalently attached (immobilized) to the SP
denstisity
-number of electron pairs a ligand can donate at one time -monodentate: can only donate 1 electron pair at a time
Electrogravimetric analysis
-plate our analyte on electrode (~ cathode) -- measure mass difference of electrode before and after the reaction -analyte would be deposited on the cathode considerations for this: -need large surface area on electrode -need to know when the reaction is done a. disappearance of color b. do not expose the entire electrode to the solution at once *expose fresh electrode and look for evidence of depsoit *if the newly exposed surface has a deposit, electrolysis is done c. qualitative test for the analyte
population vs sample
-population: collection of all possible measurements from a whole population -sample: portion of all possible measurements from a population ("sample/selection" from a given population)
coagulation of colloids
-positive ions around lattice attract negative ions in layer and causes double ionic layer which prevents lattice from growing in size and precipitating
particle size of precipitate is influenced by
-precipitate solubility -temperature -reactant concentrations -rate at which reactants are mixed
precipitation from homogeneous solution process
-precipitating agen is generated in a solution of analyte by a slow chemical reaction -local reagent excess do not occur -as result, relative supersaturation is kept low
Standard reduction potential (SRP)
-predicting the voltage when different half-cells are connected to each other; E^degree symbol are measured through a standardized experiment -the SRP is the DIFFERENCE between the standard potential of the rxn of interest and the potential of of SHE (which you can set to = 0)
electronic tranisitions
-promoting an electron from 1 MO to a higher MO -examples: *electronic transition = UV-Vis *vibrational transition = IR *rotational transition = mircowave -EVERY molecule will have lowest E state - aka ground state (1 ground state per molecule) -any higher energy state = excited state -absorbance goes from ground to excited state
Electrical current (I)
-quantity of charge flowing each second past a point in an electric circuit *quanitity of charge transfer per second -measured in Amperes = C/s
Precision
-reproduciblity
chromatogram and how to read it
-results of a chromatography experiment -to = air or something that does not interact with the SP -tr = retention time (which is characteristic of each molecule) *different tr's at each peak in the graph *characteristic or each solute/MP /flow rate combination so changes with each molecule (solute) -tr' = tr - t0 = aka the adjusted retention time -1 peak per 1 solute and 1 solute per 1 peak -peaks in graph should be gaussian (follow "normal" curve distribution) -h = height of curve -W = width of curve -W 1/2 = width at half height where, 1/2 h = half height of curve
Cl mass pattern in mass spec
-see the isotope 35Cl and 37Cl in a 3:1 ratio on the mass spec 35Cl: 75% and 37Cl: 25%
Br pattern for mass spec
-see the isotopes for Br in a 1:1 ratio 79Br and 81Br come in a 1:1 ratio
particle growth
-small number of particles -large sized particles -dominant in solutions with low relative supersaturation (crystalline solution)
Titration of a mixture
-smaller Ksp means less soluble which means that the species with the smaller Ksp percipitates first -when the two Ksps are sig. different, the first ppt. reaction may be nearly complete before the second even begins -the less solube ion, with the lower Ksp is the first to percipitate, hence the first equiv. point
photo diode array
-some wavelengths get absorbed and some do not get absorbed *not wavelength by wavelength *measures all wavelengths that hit the prism but only select wavelengths hit the prism -photodiode measures all wavelengths that hit it -very fast (seconds) -less sensitive instrument (limited to approx. 2nm resolution)
acid
-substance that increases the concentration of H+ in aq. solution (H3O+, hydronium ion) -H+ is also known as a proton -Bronsted/Lowry def: acid is a proton donor, loses a proton *H3O+ would lose a proton to become H2O
chromatography
-technique for separating compounds in a mixture by passing a mixture through a solumn that retains some compounds longer than others -it is widely used for, 1. qualitative analysis: what is the identity of the compound? 2. quantitative: how much of a component is present?
Grubbs test for an outlier
-the Grubbs test will tell us whether or not we should eliminate a data point from our data set (normally test the max or the min as the outliers) -only remove ONE DATA POINT (only ONE) -use the equation in the image below for the Grubbs test, and if Gcalc > Gtable, than we eliminate that data point from the data set -after you remove a data point from a data set you have to recalculate the standard dev and the mean -if Gcalc > Gtable, <5% chance that the difference is due to random error so we remove this data point BUT, if Gtable > Gcalc, >95% chance that the difference is due to random error so we keep the data point
Absorbance total
-the absorbance at any wavelength is the sum of absorbance for each species in a mixture at that particular wavelength so, Atotal = A1 + A2 -- (ECL)1 (ECL)2 -to measure the concetration of all species in a solution, we need to measure as many absorbance wavelengths as we have solutes *need to be careful with indexing here*
Indicator electrode
-the electrode that responds directly to the analyte, either transferring electrons to or from the species of interest (analyte) -potential varies in response to analyte concentration -responds to analyte concentration -the potential of the indicator electrode is E+
SB/SA titration
-the equiv. point will still be at pH = 7 -it will start with a pH > 7 though because starting out with excess base -will go to pH < 7 after the equiv. point because you will have excess acid -the SB is the analyte and SA is the titrant
Sig. Figs
-the intermediate result should have at least one more significant figure. Do the rounding on the final result not the intermediate results to avoid round-off errors
Uv-Vis
-the light source is a kind of lamp *Deterium (D2) lamp -- UV wavelength *W light bulb -- visible wavelength (these are switched around at approx. 360 nm) -we are looking at A wavelength by wavelength -different wavelengths are detracted at different amounts
***[H+] in a problem***
-the max [H+] from water = 1.0 * 10^-7 -if [H+] from acid > 10^-6, can ignore [H+] from water -if [H+] from acid < 10^-6, calculate totals with concentration from water -calculate H+ using ICE table and then add the x you find to the concentration of the H+ already present
Reducing agents
-the molecule that is oxidized in the overall rxn -the products in the reduction half reaction
Oxidizing agents
-the molecule that is reduced in the overall rxn -these are the reactants in reduction 1/2 reactions
Formal potential
-the potential for a cell containing a specified concentration of reagent other than 1 M (aka the potential at non-standard conditions) -E without the degree symbol in exponent
quantitative separation
-the resolution needs to be greater than or equal to 2 -if greater than or equal to 2, it is said to be fully resolved -increasing the column length increases the resolution -if you double the column length, increases the resultion by ~sqrt(2), which ~ 1.41
single beam spectrophotometer
-the sample and the blank are measured by the detector at different points
Resolution (for chromatography)
-the smaller the plate H, the narrower the peaks, and the better separations you get *meaning, the narrower the peaks = better resolution
acids and bases
-the stronger the CA, the weaker the CB -the weaker the WA, the stronger the CB (just a comparison) -strength depends on a Ka but can look at it qualitatively too -pH depends on BOTH Ka and concentration -
Direct titration
-the titrant is added to the analyte until the end point is observed
Gravimetric titration
-the titrant is measured by mass and not volume -titrant concentration is expressed as moles of reagent/kg of solution -provides 3X more precision than volumetric titration -can use a pipet rather than a buret in gravimetric titration -always better to use gravimetric titration -- should be the standard
***T-test
-there are two different routes you can go with the T-test depending on whether or not you passed the F test -student's t compared the means from experiments to be used in the confidence interval 2 CASES OF THE T-TEST: 1. if we PASS the F-test, standard devs. are statistically the same, we use the t-test where you have to calculate Spooled 2. if we FAIL the F-test, standard devs. are sig. different, we used the t-test where there is no Spooled *need to caculate the degrees of freedom to see where to look on the Ttable What to do with the results: -if the Tcalc > Ttable than the difference is statistically significant *greater than 95% that the difference is sig. -if Ttable > Tcalc, the means are not statistically different *less than 95% confident that the difference is sig.
common ion effect
-there is more than one source of (one of) the ions in the salt -a salt is less soluble in solution if one of its consitient ions is already present in the solution *due to the nature of Le Chatelier's principle -in these types of problems, need to add the M of the ion in solution to the other ion in the ICE table
Blank titration
-there is no analyze present in the solution -you just have your titrant -just gives us how much titrant it takes to react with the indicator -volume at the equiv point = volume at end point - volume of blank *blank is used as a standard
Strong acid and bases
-they completely dissociate in aqueous solution -meanign equil. constants are quite large for these -if a strong acid is when K >> 1, Ka and/or Kb >> 1 -strong acid and base, product side -strong acid is stronger than H3O+ -can assume these reactions go to completion, treat them as at 'equilibrium'
Nernst equation
-this is the Nernst equation at 25 degrees C -there is a different Nernst equation that is not at 25 degrees C -expresses net driving force for a redox reaction -changing the coefficients in a reaction (like changing the balanced equation) -it is an intensive property, it does not matter how much you have but it is the driving force of the redox reaction
Kf
-this is the equilibrium constant for the reaction of a metal with a ligand -called the formation constant or stability constant -formation constants for ETDA complexes are large and tend to be larger for more positively charged metal ions *NOTE: Kf is defined for reaction of the species Y4- with the metal ion, and at low pH, it is not always in this form (Y4- form shown in attached image)
colloidal suspension
-tiny particles (10^-7 to 10 ^-4) cm in diameter -show no tendency to settle from solutions -difficult to filter
pH
-to find pH you need to find the H+ concentration in solution
oxidation and reduction basics
-to say something was oxidized means it lost electrons -to say something was reduced means it gained electrons
detector
-turns photons into electrical signal that we can read -measures wavelength by wavelength -very sensitive -sub-nm resolution -time intensive (hours)
atomic machinery facts
-typical atomic line widths *10^-3 through 10^-2 -typical molecular bandwidths *10-100 nm
Voltaic cells equilibrium
-under concentrated conditions where there is NO net driving force -there is NO VOLTAGE, V = 0.00 when the cell is at equilibrium -in this case, Q = K and the Ecell = 0 so have to rearrange Nernst equation -if there is a positive E(stand.) in standard states, the forward direction of the reaction is spontaneous, K > 1 if there is a negative E(stand) in standard states, reverse direction is spontaneous, K < 1
Helpful rules for mass spec
-use cluster calc., if you have a cluster of peaks, you can subtract the second peak from the original one and use this ratio to calculate your charge and then use the charge to get the entire mass (difference between cluster peaks should be ~ 1) -13C can be used to get amount of carbons in experiment: if you get the relative abund., can use this and the 12C abund. to calculate carbons in molecule 1.1% 13C * 12C [x] = 13 % (rel. abund.) 12C [x] = 11.8 = 12 12C in molecule
Monochrometer
-use diffraction grating to send different wavelengths to different points in space -how far apart two wavelengths are in space depends on the overall change in wavelengths -monchrometer bandwidth magnitude of range of x coming out of monochrometer *for example, monochrometer set to 450 nm with a 5 nm bandwidth -- 447.5 -452.5 coming out of the monochrometer -molecular absorbance bandwidth = range of wavelength molecule absorbs -the banwidth is normally smaller though, around 1cm -trade-off between resolution and signal: the narrower the exit slit, the greater the ability to resolve closely spaced peaks and the noiser the spectrum *thus, resolution of closely spaced bands, which require a narrow width slit, can be achieved at the expense of decreased signal-to-noise ratio -1/5 (absorb. bw) >/= (monochrometer bw)
Amperometry
-use magnitude of current, not the duration, to find the concentration -measure the electrical current between a pair of electrodes that are driving an electrolysis reaction -one of the reactants is the intended analyte and the measured current is proportional to concentration of analyte -at applied voltage, the amount of current is proportional to [ ] -concentration, voltage, and current are all related -single point measurments
Standard Addition
-use when calibration curve is unreliable - known quantites are added to an unknown to increase the concentration. of analyte - signal acquired - standard additions are especially useful when matrix effects are important - standard & analyte are the same substance
Acid/base titrations
-using a standard solution to measure a property of an analyte solution
volumetric titration
-using volume of added titrant (typically in mL)
Potential difference
-volt meters measure difference in potentials between two half cells and their directionality -electrons should flow spontaneously from left ro right, anode to cathode -a negative potential difference indicates spontaneous directionality from right to left, cathode to anode -measure potential DIFFERENCE
concentration cell
-voltaic cell that uses redox couple @ both electrodes -if sit for a long period of time, the concetrations diffuse through the salt bridges through the voltaic cell -either anode or cathode side starts with very low concentration
Note about K, equilibrium constant
-when K is really large, it is sometimes okay to write the reaction SOLELY in the FORWARD direction, ---->, instead of writing the reaction with double-headed arrows *10^9 is large enough for our purposes where can ignore the reverse reaction -just means that the reaction goes to completion very rapidly
Electrical work
-when charge is transferred, energy is involved -energy that results in a change in position = work -if charges spontaneously move away from like/towards opposite charges, energy can be harnessed as work -if charges are forced toward like charges/away from opp. charges, work (energy) must be done -it cost energy to move like charges towards each other and energy is released when opposite charges move away from each other
comparing solubilities
-when different salts are dissolved in pure water, their Ksps can be compared directly to see how they compare to the different equiv. points -EXCEPT the ions have to have the same charge
pka and pH
-when pH = pka, the solution is at the 1/2 equiv. point -buffer capacity is at the maximum when pka = pH -this is where [A-] = [HA], where the [conjugate base] = [the acid] -if [A-] / [HA] changes by a factor of 10, pH changes by one unit (either up or down direction)
isobestic point
-where two species have the same molar absorbtivity constant (E) -for a reaction where A goes to B, no matter the spectra, it would always pass through Isp point -the presence of an isobestic point during a chemical reaction is a good indicator that only two principal species are present
polyprotic acids and equilibrium
-with high enough concentration in intermediate form of species, everything should have ~ pHs regardless of concentration
Terminology with sample vs population problems
-x with a bar over it refers to the mean of a sample *and this approximates the mean of the population -curvy M ("mew") refers to the population mean -s refers to the sample standard dev. while delta (the symbol) refers to the population standard dev. *s approximates delta -accuracy in this case refers to how well the sample mean matches the population mean -precision refers to how well our measured means match each others, so this can be determined by standard dev.
***Indicators and titration***
-you basically are titrating the "indicator" because when the indicator reacts with the titrant, it makes a physical change (a color change) IMPORTANT POINT: -titrant volume at the end point = vol. titrant that reacts with the analyte + vol. of titrant that reacts with the indicator
How to get mmol
-you multiply M of species * mL -and to get back to M, you just divide by mL
Steps to a titration problem
-you need to find the moles of the titrant and then can convert the moles of titrant to the moles of analyte used (via the ratio of these species in the reaction) -then divide by the volume of analyte added to get M -need to be careful and look at stoichiometry -AgNO3 is a primary standard
MORE REALISTIC TO CALC estimate of weird u and estimate of weird o (sample standard dev instead of pop standard dev)
...
at concentrations exceeding ____ M, avg distances between ions are diminished to point where each particle affects the charge distribution and thus the extent of absorption of its neighbors
0.1 M
specific gravity means
1 L solution = # kg
ppt
1 g/L 1 mg/mL
ppm
1 mg/kg 1 microg/mL
ppm (4 equiv)
1 microgram/ml, 1 mg/L, 1 x 10^-6 g/mL, 1 x 10^-3 g/L
ppb
1 ng/mL 1 microg/L
HPLC - stationary phases SILICA: Adsorptive centres on the surface of silica: Free silanols - "..." Geminal silanols - "..." Silanols near metal cations - "..." Associated (vicinal) silanols - "..." Siloxanes - "..." pH stability of silica: "..."
1 silanol group - slightly acidic; sorption sites for basic compounds 2 silanol groups - not acidic 2 associated silanol groups - not acidic; sorption sites for compounds with OH groups strongly acidic; they increase heterogeneity of the surface and can badly affect the separation of basic compounds products of the condensation of associated silanols 1-8
Internal Standard Steps
1) establish the F value - can calc. using a known [X] & [S] 2) figure out [X] with known values of F and [S], and measuremetns of Ax & As
General steps in a chemical analysis
1) formulate a question 2) select appropriate analytical procedure 3) take your sample 4) prep your sample 5) analyze your smaple 6) report and interpret 7) draw conclusion
Constructing a Calibration Curve ***NEED TO KNOW****
1) prepare known samples of analyte covering a range of .concentration expected for unknowns 2) measure response of analytical procedure to these standards to generate data (spectrophotometer) 3) subtract average absorbance of blank samples from each measured absorbance to obtain 'corrected absorbance' 4) make a graph of 'corrected absorbance' vs. 'quantity' 5) add least-square regression
Common fragments to see in mass spec
1. -CH3 : 15 Da 2. -OH, -NH3 : 17 Da 3. -OCH3 : 31 Da 4. -CH3CO, -C3H7 : 43 5. -C2H5 : 29
Error propagation -- only regarding random error in an experiment
1. Addition and Subtraction -use absolute uncertainties -equation: Easbol. = sqrt( (e1^2 + e2^2 + e3^2....) ) -relative uncertainty can be found at the end of the absolute uncertainty calcs. 2. Multiplication and Division -use percent relative uncertainty to calculate the uncertainty and absolute uncertainty can be calculated at the end of these problems -first you need to convert absolute uncertainties to relative uncertainties, do the calculation and then multiply the relative uncert. by the measurement and that gives you your absolute uncert. 3. Mixed Operations -say you have a problem that has addition and then division -first you convert the numerator to absol. error and then you convert num. and denom. to relative error and solve for relative error -once you have that, just multiply by the numerical measurement answer and that will give you your absol. uncert.
5 types of chromatography
1. Adsorption chrom. 2. Partition chrom. 3. Ion-exchange 4. Molecular exclusion 5. Affinity
Strong bases
1. LiOH, lithium hydroxide 2. NaOH, sodium hydroxide 3. KOH, potassium hydroxide 4. RbOH, rubidium hydroxide 5. CsOH, cesium hydroxide 6. R4NOH, quaternary ammonium hydroxide -tend to be metal hydroxides -Kb >> 1 -stronger than OH- -treat as limiting reagent problem, use the one with the less moles -amines are normally weak bases and need to consider equil., and Kb << 1
Molality vs Molarity
1. Molality: mol solute/ kg solvent (not total soln.) *masses of solute and solvent do not change with temp (as long as neither species evaporates), SO molality does NOT change when temp changes 2. Molarity: mol solute/ L solution *DOES change when temp changes because the volume of solution normally increases when it is heated
Types of interference with the light source
1. Spectral interference -absorbance or emission lines over lapping analyte element -eliminate by analyzing a different light 2. Chemical interference -when other things in the sample inhibit atomization -use releasing agent to reduce effects of atomization inhibitor 3. Ionization interference -atomizers can ionize atoms -Fe and Fe2+ have different absorbances and emission -ionization suppressors work by providing something that ionizes easily -- alkaline metals
precipitation gravimetry procedure
1. analyte converted to soluble precipitate 2. precipitate is filtered 3. it is washed free of impurities 4. converted to product of known composition by heat treatment 5. weighed
How to make a buffer
1. choose approx. WA/WB conjugate pair 2. determine needed [A-] / [HA] 3. a) add WA and WB directly to get correct ratio b. start just with WA or WB and add SB or SA to get correct ratio of [A-] / [HA]
Mixture of Ca2+, Mg2+, and Fe2+
1. direct titration with EDTA, gives [Ca2+] + [Mg2+] + [Fe2+] 2. 2nd aliquot -- mask Fe2+ -titrate with EDTA now gives [Ca2+] + [Mg2+] 3. 3rd aliquot, mask Mg2+ -titrate with EDTA to give [Ca2+] + [Fe2+] (I think you can only mask one metal at a time? )
Important components of spectrophotometer (4)
1. light source 2. wavelength selection 3. sample cuvette 4. detectors
steps for external standard calibration
1. prepare concentrated solution (stock solution). 2. dilute different concentrations 3. use machine to evaluate intensity of signal of serial dilution prepared 4. find math relationship between concentration and signal of machine
3 electrode system
1. reference electrode: const. potential to measure against 2. working electrode: indicator electrode from galvanic cells, reaction of interest happens here *1 and 2 measure potential between these two 3. auxiliary electrode: current carrier *2 and 3 measure current between these two
3 Methods of calibration
1. simple calibration curve 2. standard additions 3. internal standards
***5 things to know in a titration problem***
1. the concentration of the titrant 2. the volume of the titrant *use 1 and 2 to calculate moles of titrant 3. concentration of analyte 4. volume of analyte *use 3 and 4 to calc. moles of analyte 5. balanced reaction between titrant and analyte *know the ratio of the moles in the reaction *need to find the moles of analyte in the reaction so use this ratio in your calculations
Detection methods to see if titration is complete
1. voltage change 2. absorbance change 3. indicator color change
uncertainty in pH and H+
1. y = log (x) -absolute error in y = relative error in x / ln(10) 2. y = 10^x -relative error in y = (absol. error in x) * (ln(10))
Indicator errors
1. your indicator choice *you want an indicator that will give you the pH at equiv. point as close to the expected value as possible 2. change color by acting with titrant *could dissociate or something in solution *you are kind of titating the indicator here
0.62M
1.35L glucose (C6H12O6) solution with a conc of 300.35 g/L was diluted to a volume of 3.63L. THIS was the molal conc of the diluted solution
Limit of quantitation (LOQ)
10* std dev
% rel. uncertainty (%re)
100 x relative uncertainty
Deci
10^-1
Pico
10^-12
Femto
10^-15
Atto
10^-18
Centi
10^-2
Milli
10^-3
Micro
10^-6
Nano
10^-9
Deca
10^1
Hecto
10^2
Kilo
10^3
Mega
10^6
pH+pOH=
14
Flask calibration at what temperature
20 C
Limit of detection (LOD)
3*std dev
Q test is used with a data set of _____ results or more
50
Spherical silica modified with ODS - (mean particle diameter, "...") The chemical stability of silica bond phases - High pH leads to ".." Low pH leads to "..."
5μm The dissolution of the silica backbone The hydrolysis of the siloxane bond
1 standard deviation from the mean
68% of data
2 standard deviations from the mean
95% of data
if coefficient of determination (r^2) is 0.99 it means
99% is ocming from the analyte of interest. the closer to 1 the better
3 standard deviations from the mean
99.7% of data
apparent mobility
= electrophoretic mobility + electroosmotic flow
1.80 x 10^10
A 0.10M solution of formic acid was titrated with a 0.10M solution of NaOH at 25oC. The equllibrium constant for this titration reaction has THIS value
pH=7.0
A 0.1M aqueous solution of HBr was titrated at 25oC with a 0.1M aqueous solution of NaOH. In this experiment, the equivalence point will be reached at THIS pH value
5.2M
A 37.50mL portion of a solution was diluted to 1.50L and the diluted solution was found to have a conc of 0.13M. THIS was the molar conc of the original solution
0.2mm
A GC column, operated isothermically at 150oC, produced 100,000 theoretical plates for n-dodecane peak. The mobile linear velocity was maintained at 40.0 cm/s and the gas hold-up time was 50.0s. The column was characterized by THIS plate height
capillary electrophoresis
A and C terms eliminate; VERY efficient
4.76
A buffer solution was prepared using the acetic acid (Ka = 1.75 x 10^-5) and sodium acetate. It will possess the highest buffer capacity at THIS pH
Stationary
A capillary zone electrophoresis (CZE) system does not have this phase
K > 1
A chemical reaction is the thermodynamically favored (spontaneous) if its equillibrium constant (k) has the following value
Mobile phase
A chromatographic technique is named after the physical state of THIS
secondary standard
A compound whose purity has been established by chemical analysis and that serves as the reference material for a titrimetric method of analysis -less pure than primary standard
4.9min
A dilute sol of anthracene and methylene chloride was spiked with methane and injected into a GC. The elution times of methane, naphthalene, and anthracene peals were 48s, 3.5min, and 5.7min, respectively. Anthracene spent THIS amount of time in the stationary phase
4.9min
A dilute solution of anthracene in methylene chloride was spiked with methane and injected into GC. Th elution times of methane, naphthalene, and anthracene peals were 48s, 3.5 min, and 5.7 min, respectively. Anthracene spent this amount of time in the stationary
Solvent used to prepare the sample
A gas chromatogram typically displays a very large early-eluting peak. This large peak represents THIS
Van deemeter eqn A, B, C, u
A is mult paths, B/u is longitudinal diffusion, Cu is equilibration time (u is flow rate)
0.106 M
A nitric acid solution was standardized using 0.4541g of the primary standard, tris (hydroxymethyl) aminomethane, (FM = 121.14). A 35.37mL volume of the acid solution was required for complete titration. The molarity of the nitric acid solution was THIS
photon
A particle of electromagnetic radiation with no mass that carries a quantum of energy
photons
A quantum, or discrete quantity, of light energy that behaves as if it were a particle.
Liner
A quartz or glass tube used in a GC injector port is known as THIS
7.52M
A researcher was using a 50.00 wt % solution of HClO4 with a specific gravity(density) of 1.512 g/mL. The solution had THIS molar conc
None of the above (analyte)
A sample consists of the matrix and THIS
1.1
A sample containing naphthalene and anthracene was injected into a GC column. Adjusted retention times for naphthalene and anthracene were 5.4min and 6.0 min respectively. The separation factor for these two peaks was THIS
2.92 x 10^14 mol/L
A sample of aqueous HCl solution of pH 1.00 was prepared at 10oC. THIS is the hydroxyl ion conc in the prepared solution
They do not differ significantly
A stock solution of Methyl orange was prepared following two different dilution schemes, Absorbance of each solution at 473nm was recorded in 13 replicates that produce the following values for the mans and SD values: Scheme 1: N=13, Mean=0.2972, SD=0.000725 Scheme 2: N=13, Mean=0.3038, SD=0.00114 THIS conclusion can be drawn regarding the precisions of the two methods at 95% confidence level
30.61%
A student was working with a 12.1m solution of HCl. The solutoon conc expressed in wt% had THIS value
Gas chromatography
A term is eliminated
outlier
A value much greater or much less than the others in a data set
3.347
A water pollutant was determined by two different methods (a): chromatographic method (n=10) and (b): spectrophotometric method (n=8). The following results were obtained: Chromatographic: n=9, Mean=72ppm, SD=1.51ppm Spectrophotometry: n=11, Mean=72ppm, SD=3.31ppm To decide whether the chromatographic method has a significantly higher precision compared with spectrophotometric method, one should perform an F-test, using THIS critical value of F (at 95% confidence level)
What part of van deemeter eqn does GC remove?
A-no different paths
Absorbance/transmittance eqn
A=-logT
Beer's Law for absorbance
A=Ebc e= molar absorptivity (M-1cm-1) b= path length (cm) c= concentration (M)
Difference bw AAS and AES instruments
AAS needs light source and temp has to be lower to keep atoms in ground state, not excited state
Difference between AAS and AES
AAS- measure amount of radiation ABSORBED by GROUND state atoms VS measure amount of radiation EMITTED by EXCITED state atoms
When to use AAS vs AES
AES can do multiple elements at a time
90.9%
AT 25oC, acetic acid is characterized by pKa value of 4.76. In acetate buffer solution of pH 3.76, THIS percent of acetic acid molecules exist in undissociated form
Hollow cathode lamps used for
ATOMIC ABSORPTION
Absolute vs. relative error
Absolute: has units, magnitude of uncertainty Relative: absolute error / the exact measurement *need to make at least two measurement to be able to determine relative error
An acid
According to Bronsted-Lowry theory, in the hydrolysis of NH3 (NH3 + H20 <-> NH4+ + OH-), ammonium ion represents THIS
Accept a pair of electrons
According to Lewis, an acid is defined as a chemical species that is capable of doing THIS
43,264
According to Purnell equation, THIS number of theoretical plates will be required to resolve a mixture of phenanthrene (k1=4.00) and anthracene (k2=4.20) by GC with Rs value of 2.0
Weak
Acetic acid is a weak acid (Ka= 1.75 x 10^5 at 25oC). Its conjugate base (acetate ion) represent THIS type of base
Proton
Acid donates this in Bronsted Lowry
Celsius to Kelvin
Add 273.15
Molality to molarity
Always assume 1 kg of water so that you can immediately know how many moles, convert to grams and add in grams of water (1000 g) to get total mass of solution. Convert to total solution volume from total solution grams. Then you have moles solute/total solution volume CH. 1 #7
Acetonitrile
Among the most popular binary mobile phases used in reversed-phase HPLC, the one with THIS organic modifier in water provides the lowest mobile phase viscosity and UV-cutoff
1.09m
An ammonium nitrate (NH4NO3) solution contained 5.00 moles of this salt in 5.00kg of the solution. The molal conc of the solution of this solution is
1.39 m
An ammonium nitrate solution containing 4.00moles of this salt in 5.00kg of the solution. Molal concentration is this
1.48 x 10^-12 mol/L
An aqueous HBr solution was prepared at 30oC with a pH of 2.00. Here, dissociation of water made THIS contribution to overall conc of hydrogen ion concentration in this solution
4.46
An aqueous buffer solution (volume 1.00L) was prepared at 25oC using 45.039g of acetic acid HA and 30.763g of sodium acetate, THIS was the pH of the resulting buffer solution
They don't differ significantly
An experienced lab tech. was asked to use a newly developed method to perform seven replicate measurements on a standard reference material (SRM) containing 64.8ppm of sulfur. The following results were obtained for sulfur conc. (ppm): 63.9, 65.9, 62.8, 64.1, 64.6, 65.2, and 62.9. A t-test performed on this data at 95% confidence level should lead to THIS conclusion regarding the experimentally obtained mean and the true value for sulfur conc.
How to carry out an analysis?
Aquisition - Sample taken must be REPRESENTATIVE of the whole Stability - Must not lose the material of interest (or change it) - unless we understand exactly how Separation - Need to separate the analyte from the matrix Analysis Reliability
Oxidation number rules
Assigning Oxidation Numbers: 1) The oxidation number of an element in an elemental form is zero. Notice in something like N2, O2, or O3, the bonds are between atoms of equal electronegativity. In this case, the shared electrons get split evenly. 2) The oxidation number of a monoatomic ion is equal to the charge on the ion. From here we get into specific atoms based on the most and least electronegative non-metals. Since metals tend to form ionic compounds, they are generally covered by rule 2 above. 3) H in compounds generally has an oxidation number of +1, except in metal hydrides where its oxidation number is -1, or when bound to B, where its oxidation number is again -1. 4) O in compounds generally has an oxidation number of -2, except in peroxides (-O-O- functional group), where its oxidation number is -1, or when O is bound to F. This is because, except for F, O is the most electronegative non-metal that forms compounds, so will always win the competition for shared electrons, again except against F. 5) Halogens usually have an oxidation number of -1, unless they are bound to a more electronegative halogen or O (except F), or have more than one bond. These first five rules give us a starting point for assigning oxidation numbers to all elements in a compound. The last two rules involve finding oxidation numbers for the rest of the elements not already specified. 6) All atoms of a single element are assigned the same oxidation number. 7) The oxidation numbers for all atoms in a compound must add up to the charge on the compound.
9.24
At 25oC, the dissociation constant for acetic acid is 1.75 x 10^-5. From this information it can be concluded that acetate ion is characterized by THIS PKb value
3.46
At 25oC, the dissociation constant for formic acid is 1.80 x 10^4. At this temperature, the pH of a 0.001M formic acid will be THIS
None of the above (not 6,8, or 10)
At 40°C, the concentration of hydronium ions in an aqueous solution was found to be 1.0*10^-6 M. This solution has a pOH value of this.
1.00 or log(10)
At equillibrium, the ratio of the rate of the forward reaction to that of the reverse reaction equals to THIS
None of the above (1 mol)
Avogadros number represents the number of elementary entities present in THIS amount of a substance
all results below the detection limit are reported as
BDL (below detection limit)
Nominal mass example calc
C3H6BrCl nominal mass: 3 * 12C + 6 * 1H + 1 * 79Br + 1 * 35Cl -molecular ion does not have to be present in this calculation
measurement uncertainty can/cannot be eliminated
CAN NEVER
Buret
Calibrated glasstube with stopcock
Problems that confuse me on sapling
Ch 3: 8,9, KNOW HOW TO USE CALC FOR STANDARD DEVIATION AND.. plotting graph if time allows
Problems to run thru from sapling for speed/confidence
Ch. 1: 2,4,7,8 (look at solution), 10,12,14,17, 18,19,20,22 Ch 2: 2 Ch 3: 4,5,6 (log/inverse log),7,8,9,11 Ch 4: PP slide 9, sapling 3,4,5,6,9,10,11,13,14 Ch : 1,2,3,5,6,7,8,11
Questions I had trouble with from PP/sapling
Chap 6 PP: problem 3
The suspect value can be thrown away
Chemical analysis of a soil sample revealed the presence of trace concentration of benzo(a)pyrene. The following conc. in data (mg/kg) was obtained in replicate measurements: Benzo(a)pyrene conc (mg/kg): 5.30, 5.00, 5.10, 5.20, 5.10, 6.20, 5.15 The value 6.20 is an outlier suspect. A Q-test at 95% confidence level will lead to THIS conclusion
Random error
Chemometric methods are applicable to analytical data that contain only THIS type of error
Two
Chromatographic separation is characterized by THIS many phases
Chromatogram
Chromatographic separation is presented in the form of a series of peaks, collectively termed as this
Sorption-Desorption
Chromatographic separation is presented in the form of a series of these events
None of the above (Botany)
Chromatography was invented in 1903 by M.S Tswett, an expert in this branch of science
20th
Chromatography was invented in THIS century
Accuracy
Closeness of mean values in replicate measurements
Precision
Closeness of replicate measurement values to eachother is expressed by THIS term
None of the above (12C)
Current definition of "mole" is based on the atomic mass of THIS isotope
Nerts Equation
Delta G= -nFEcell
Accuracy
Dif bw measured value and actual value, usually expressed as absolute/relative error
Preparing solution. Method 2
Dilution from a concentrated solution -M1V1=M2V2 -the above equation stands as long as M1 and M2 have the same units and V1 and V2 also have the same units
None of the above
Dissocation of water (H20 <-> H+ + OH-) is characterized by the following equilibrium expression: Kw= (H+)(OH-)/ (H20) Here, H+ has THIS unit
46.8ppb
Drinking water was analyzed for lead content , and the following statistical data were obtained in ten replicate measurements: (a) S.D=2.2 ppb ; (b)RSD 4.7%. From this data it can be concluded that THIS was the mean lead conc in the analyzed water sample
Split vent
During split injection in GC, most of the injected sample goes through this
Energy of a photon
E=hv or E=hf
nonspontaneous electrochemical reaction
Ecell < 0
spontaneous electrochemical reaction
Ecell > 0
End point vs equiv point
End point: the abrupt change in physical property, such as pH and indicators, that we measure to locate the equivalence point Equivalence point: defined by the stoichiometry of the reaction *moles titrant = moles analyte (stoichiometrically)
None of the above (no units)
Equillibrium constant is expressed in THIS unit
Why use an internal standard?
Everything is measured relative to the internal standard. - Poor volatilising samples - Injection consistancy - Day-to-day reproducibility
the confidence interval for the mean of five measurements is bigger than that of a single result (T/F)
False
atomizer -- flame
Flame -- relatively low temp. Pros: -cheap -does what it needs to do and is efficient -easy to use -not breakable because flame is a flame Cons: -reuqires a lot of sample -- only 5% of each sample will get fully atomized -reductive envrionment, lots of oxides and hydroxides formed -low temp. stability
Is fluorescence or absorption spectrophotometry more sensitive? Why?
Fluorescence because light source is not measured; it is just emitted photons that are measured in fluorescence, machine does not have to detect small difference.
Displacement titration explained part 2
For metal ions that do not have a good indicator a second titration method is the displacement titration. Here the analyte is treated with an excess of a second metal bound to EDTA. The analyte ion displaces the second metal from the EDTA complex, and then the second metal is titrated with EDTA. A typical displacement titration involves Hg2+ as the analyte and MgEDTA at the displacement titrant.
0.0mm
For open tubular columns, THIS is the value of eddy diffusion term in Van Deemter equation
To the right
Formation of ethylene from ethane (C2H6 <--> C2H4 + H2) is an example of endothermic reaction. Application of heat from an external source will shift the equilibrium of this reaction in the following manner
Hydronium ion
Free hydrogen ions cannot exist in aqueous media; they exist in a hydrated form known as THIS
Immobilzation
GC column technology involves a process by which individual chains of a polymeric stationary phase are crosslinked with each other. THIS Step in column fabrication is known as this
Common strong acids (6)
HCl, HBr, HI, H2SO4, HNO3, HClO4 (all ic acids, except for HBr and HI)
EDTA pka values
Hexaprotic acids 1. pka1 = 0.0 2. pka2 = 1.5 3. pka3 = 2.00 4. pka4 = 2.69 (these are all of the carboxylic, oxygen protons) 5. pka5 = 6.13 6. pka6 = 10.37 (these are the amino protons) *so the oxygen protons have much lower pka values than the amino protons (lower pka just means stonger acid so makes sense) -at low pH, H+ competes with metal ion for EDTA while at high pH, OH- competes with EDTA for metal ion
atomic absorption light source
Hollow-cathode lamp (HCL) -contains atoms of the element being studied -uses electrical current to excite atoms -emits photons as they relax (emitted hV = light source) -need a different lamp for every element -HCL runs at a lower temp and pressure than the analyte of the sample *broadening effects are decreased in HCL but are prominent in the sample -blanking done by magnetic fields, zeeman effect -a lamp with matching cathode material is required for each element -atoms emit the same wavelengths they absorb so need to use the same element to absorb atoms
ACCURACY: PRECISION:
How close is the result to the true value? How close together are repeat measurements?
***F test
How to use the F-test: -F-test deals with standard deviations -F-test = comparing standard deviations from two data sets -before comparing means, we first have to consider whether or not the satndard deviations of the two data sets are statistically different or not -null hypothesis: the standard devs. from the 2 data sets are the same -Fcalc = s1^2 / s2^2, where s1 > s2 *where s^2 = variance What the results mean: You compare your Fcalc to the value in the Ftable, -if Fcalc > Ftable, you failed the F-test and the null hypothesis is not true -- your standard devs. are statistically different -if Ftable > Fcalc, you pass the F-test and the null hypothesis is true -- your standard devs. are statistically the same
1.0
Hydrolysis of ammonia (NH3 + H2O <--> NH4 + OH-) has the following equilibrium expression: K=[NH4+][OH-]/[NH3][H2O] Here [H2O] has the following value.
Example of an ICE table
I nitial concentration C hange in concentration E nd concentration -in an ICE table, the x refers to the solubility -ICE table is a concentration table
N-rule
If the nominal mass is even, need even amount of Nitrogens (can even be 0) If nominal mass if odd, need odd amount of Nitrogens
Overloading
In GC, peak fronting is a sign of this
Gas hold-up time
In GC, the time spent by a solute in the mobile phase is called this
To the right
In Haber process, ammonia is synthesized from nitrogen and hydrogen (N2 + 3H2 <--> 2NH3). Application of higher pressure to this system will shift the position of equilibrium in the following manner
+/- 3σ
In Normal distribution, 99.7% of the data points are located within THIS span around the population mean
0.25mm
In a GC experiment, a 30m long fused silica capillary column produced 120,000 theoretical plates. The plate height had this value
20m
In a GC experiment, a fused silica capillary column produced 100,000 theoretical plates with a plate height value of 0.20mm. THIS was the length of the column
102,400
In a GC run, phenanthrene peak was eluted at 8.0min, the peak width at the base being 0.1min. The number of theoretical plates generated by the used column was THIS
None of the above
In a GC system equipped with an open tubular column and an FID, the mobile phase flow rate through the column was 1ml/min. THIS should be the make-up flow gas rate to ensure optimum conditions for the FID operation
None of the above (both reverse and forward rxn don't stop)
In a chemical process, THIS takes place at equilibrum
Q < K
In a chemical reactor, the reaction has not yet reached equilibrium; the reactants are still being converted into the products. Here, THIS relationship holds true for the reaction quotient (Q) and equilibrium constant (K).
Gaussian
In a chromatographic zone, concentration of the analyte molecules follow THIS type of distribution
Degrees of freedom
In a data set, the number of data points that can be independently specified is known as
42s
In a gas chromatographic run, anthracene peak was eluted at 6.30min. The adjusted retention time of anthracene was 5.60min. From this data it follows that anthracene molecules spent THIS amount of time in the mobile phase
10.0
In a gas chromatographic run, naphthalene peak was eluted at 8.25min with a gas hold-up time of 45.0s. The retention factor of naphthalene had THIS value
Accept
In a signficance test, if the calculated value of the test statistic smaller than its critical value, then one should do THIS with the null hypothesis
End point
In a titration experiment, the color change of the indicator corresponds to this point of titration
Acetate ions
In acetate buffer, the buffer action is provided by acetic acid molecules and THIS chemical species
Na2CO3
In acid-base titration, this regaent can be used as a primary standard for the titration of an acid
6.27
In an acid-base titration experiment, 50mL of a 0.02M solution of MES (PKa=6.27) was titrated with a 0.10M solution of NaOH at 25oC. The system will acquire THIS pH after addition of 5.00mL of the titrant
None of the above
In an acid-base titration experiment, a 0.2M solution of HCl was titrated at 25oC with a 0.05M solution to KOH. Here, the equillibrium constant for the titration reaction had THIS value
60.94
In an acid-base titration experiment, a 75.00mL volume of 0.13M ammonium hydroxide solution was titrated with a 0.16M HCl. This system will no longer represent a buffer system after the added volume of the titrant exceeds THIS threshold value
Hydronium ion
In an aqueous solution, hydrogen ion cannot exist in a free state; upon formation, combines with a molecule of water to form THIS ion
Surface coating
In an open tubular, the stationary phase represents
MS
In chromatography, THIS detector is widely used for qualitative analysis
1.5
In chromatography, THIS value of Rs corresponds to the baseline resolution
1.0
In chromatography, THIS value of separation factor corresponds to co-elution of two peaks
Qualitative
In chromatography, a MS is primary used as a detector for this type of analysis
Plant pigments
In his pioneering research that led to the invention of chromatography, Mikhail S Tswett was trying to separate THIS type of samples into individual components
Liquid
In liquid-solid chromatography (LSC), the mobile phase is in this physical state
Solid
In liquid-solid chromatography, this is the physical state of the stationary phasw
Nonpolar
In reversed-phase HPLC, the stationary(solid) phase is characterized by THIS type of polarity
An acid
In the hydrolysis of ammonia (NH3 + H20 <-> NH4+ + OH-), water serves as THIS
Hydroxyl ion
In the hydrolysis of ammonia, this represents conjugate base of water
***atomizer -- ICP
Inductively coupled plasma -hottest atomization source (hundreds of K) Pros: -solvent evaporation happens elsewhere and no plasma energy is wasted -eliminates a lot of the interference because twice as hot and long residence time of analyte in the plasma is twice as long Cons: -expensive -hard to operate -takes a lot of time to upkeep -less sensitive than a furnace (but higher sensitivity than a flame)
RP-IP-HPLC, Chromatographic separation of charged analytes can be achieved by "..." For strong and weak organic acids, "..." can be used For strong and weak organic bases, "..." can be used
Ion pair formation Quaternary alkylamines Alkyl/Arylsulphonates
What elements of LC is pH dependent? pH influences "..." The pH level affects the degree of "..." and free (residual) silanol groups on the surface of stationary phase:
Ion-exchange chromatography Ion-exchange mechanism is controlled by pH Reversed-phase HPLC retention time and peak shape dissociation of acidic/basic compounds
why do we care about atomization temp so much?
It effects, -degree of atomization -state of atoms (ground state, excited state, etc.) -atomizers excite the atoms
Relation bw Ka and Kb for conjugate acid/base pairs
Ka times Kb= Kw
T in gibbs equation is in...
Kelvin
N (number of theoretical plates) should be large or small for good resolution of peaks
LARGE
Do emitted photons have more or less energy? Longer or shorter wavelengths?
Less energy, longer wavelengths
Common strong bases (6)
LiOH, NaOH, KOH, RbOH, CsOH, R4NOH
Dilution formula
M1V1 = M2V2 -mass (concentration typically in molarity) and volume (typically in mL or L of solution)
Tare
Mass of empty vessel in balance pan is called this
Density
Mass/ Volume = g/ mL
Systematic error
Measurement accuracy is affected by THIS type of error
Molarity
Moles/Liter -M
Sample preparation
Most error-prone step in chemical analysis
FID
Most sensitive detector in GC
number of degrees of freedom
N-1
for the residual should trend be noticed?
NO TREND
0.14
Nine replicate measurements were made on the moisture content of a silica sample and produced the following values (mg/g): 4.00, 3.70, 3.93, 3.88, 3.89 ,3.90, 4.11, 4.14, 3.80 The S.D for these measurements has THIS value (mg/g)
Solvent extraction Fraction extracted = "..." Which can be simplified to "..."
No. of moles in Solvent 1 / Total no. of moles present D/(D + V(w)/V(0))
Difference bw molecular and atomic spectroscopy
One measures molecular absorbance, one measures atomic absorbance (trace element), similar equipment but atomic needs atoms to be atomized somehow (3 ways)
Photomultiplier tube acronym
PMT
Metabolism phases -
Phase 1 (functionalisation): chemical modification of the original xenobiotic molecule by oxidation, reduction or hydrolysis (may 'activate' the compound!) Phase 2 (conjugation): conjugation reactions, in which a second, hydrophilic molecule such as glucuronic acid is added to the molecule.
for vibrational energy levels
Phosphorescence energy < Fluorescence energy < Absorbance energy Where, - E = plank's constant (h) * frequency (looks like a fancy v) - for wavelengths, it is indirectly proportional to energy of the light HENCE, the greater the energy, the shorter the wave length so for the relative wavelengths, Absorbance < Fluorescence < Phosphorescence
Perrin
Proposed Avogradros constant
Second-eluting peak
Purnell equation expresses resolution b/w a pair of chromatographic peaks through chromatographic characteristics of this peak of the pair
outlier can be tested by using a __ test
Q test
SiO2
Quartz, the preferred material for a GC linear, represents highly pure form of this oxide
Precision
Random error affects THIS characteristic of experimental measurements
Titrant
Reagent solution of known concentration which is used to react with target analyte is called this
MSDS
Red: 3 fire Blue: 2 health white: - contact hazard Yellow: 0 reactivity hazard 0= low to 4 high
Standard hydrogen electrode
S.H.E -the left-half cell is called the standard hydrogen electrode -it consists of a catalytic Pt surface in contact with an acidic solution in which [H+] = 1 M -standard species must be: pure solid, pure liquid, dissolved species at [1 M], or gas at 1 bar pressure
SENSITIVITY - want very high "..." - preferably "..." Define a "..." as a concentration that gives a peak with height of "..."
SIGNAL TO NOISE ratio, < 1% noise minimum detectable level twice the mean noise level
Should H (theoretical plate height) be large or small for better resolution of peaks
SMALL
Advantages of RP-IP-HPLC: (2) (S S) Disadvantages: (S) RP-IP-HPLC should be used when other methods (reversed phase and ion-suppression modes) have failed or when the sample contains both "..."
Separation of mixtures of acids, bases and neutral compounds and also amphoteric molecules Selectivity can be influenced by the choice of the counter ion Reduction of the sensitivity of detection non-ionic and ionic compounds
1.17%
Seven replicate measurements on a test solution produced the following results for the conc. of sodium ion (mg/L): 63.91, 65.92, 64.98, 64.24, 65.45, 65.82, 65.11. THIS is the R.S.D for these measurements
What effects can we exploit to separate compounds? (4 key ones, 2 lesser)
Solubility Ionic Interactions Van der Waals Forces dipole-dipole, dipole-induced dipole, dispersion Hydrogen Bonding Size Shape
None of the above (Lochsmidt)
THIS Austrian school teacher was first to determine the number of molecules contained in 1cm^3 of an ideal gas
M1V1 = M2V2
THIS IS ONLY GOOD FOR 1:1 TITRATIONS So, then you have to think about the equiv. points and what happens at the equiv. points *before equiv. point, you have excess analyte *after the equiv. point, you have excess titrant (because all of the analyte has reacted with the titrant)
Static Coating
THIS coating technique is most commonly used to prepare an open tubular GC column
Molality
THIS conc unit is commonly used in physico-chemical experiments in which temperature of the system may change
FID
THIS detector CANNOT be used to detect nitric oxide in air by GC
Hydrogen
THIS gas burns at the nozzle of a flame ionization detector
Waage
THIS is one of the two Norweigan scientists who discovered law of mass action
Kilogram
THIS is the SI unit for mass
4.6mm
THIS is the typical internal diameter of an HPLC column
Law of mass action
THIS law describes the state of equillibrium
4.837 x 10^13
THIS many molecules are present in 2.25ng of carbon monoxide(CO)
None of the above (fused silica)
THIS material is used as the tubing for GC capillary column
None of the above (Van Deemter Plot)
THIS plate height vs carrier gas linear velocity plot is known as this
Polyimide
THIS polymer is commonly used to create a protective coating on the outer surface of a fused silica capillary column
FID
THIS represents the most widely used detector in GC
One-tailed f test
THIS significance test should be performed to decide whether a new analytical method is significantly more precise than the standard method
None of the above (Q-test)
THIS significance test should be performed to identify an outlier in a data set
Solid-phase microextraction (SPME)
THIS technique allows solvent-free sample introduction in GC
Packed
THIS type of column is commonly used in HPLC
33.6g
THIS weight of sugar is contained in 200.0mL of a 15 wt% sugar solution with a density of 1.12g/mL
R.L.M Synge
The 1952 Nobel Prize in chemistry was awarded to AJP Martin and THIS British biochemist for their invention of liquid-liquid partition chromatography
0.49
The absorbance scale of a spectrophotometer was tested at 254nm wavelength with a standard solution. Ten replicate measurements of the absorbance with the spectrometer gave the following results: Mean=0.47; S.D=0.03. The 95% confidence interval of these measurements will have THIS value as its upper confidence limit
5.71 x 10^-10
The acid dissociation constant (Ka) of acetic acid at 25°C was found to be 1.75*10^-5. Under these conditions, the base hydrolysis constant (Kb) of the acetate ion should be THIS
71.34nM
The conc of benzo(a)pyrene (MW=252.31) in a sample of drinking water was determined to have this value of 18.00ppb. The molar conc of this carcinogen in that sample of drinking water should have THIS value
25oC (or 298K)
The conc of hydroxy ions in pure water is 1.0 x 10^-7M. This statement is true only for THIs temperatur
absolute error
The difference between a measured value and the true value.
None of the above
The dissociation of HCl (HCl <--> H+ + Cl-) has an equilibrium constant value of 2.00*10^-6 at 25°C. Given the gas constant = 8.314472 J/(K.mol), Gibbs free energy change (∆G°) for this reaction has this value.
12
The following data give the recovery of bromide from spiked fruit samples measured by a chromatographic method. The same amount of bromide was added to each specimen Apple: 777, 790, 759, 790, 770, 758, 764 Pear: 782, 773, 778, 765, 789, 797, 782 A t-test was performed at 96% confidence level to compare the mean recoveries of bromide from these two types of fruits. Here, the crtical value of t corresponds to THIS many degrees of freedom
Protons
The identity of an element is determined by its atomic number which refers to the number of THESE particles in the nucleus of each atom of the element
pKa
The inflection point on the slowly ascending first part of the titration curve representing neutralization of a weak acid with a strong base represents this
212.1 mm
The maximum height of a Gaussian distribution curve has a value of 350.mm. The inflection points on this curve will be located at THIS height
Eleven
The nucleus of lithium atom (^7Li) contains THIS many down quarks
7.0
The pH of a 1.0 x 10^-10 M solution of NaOH at 25oC will be THIS
Effects of temperature in HPLC: Advantages of increase in temperature: (3) (V F P) Disadvantages of increase in temperature: (2) (D VP)
The performance of the column often increases because of the decrease of mobile phase viscosity Analysis time decreases due to the possibility of using higher flow rates of the mobile phase It is necessary to work at higher temperatures if the mobile phase is viscous - less pressure is needed to pump the mobile phase Solvent or sample are more likely to decompose The vapour pressure of the solvent rises, thus increasing the risk of bubbles in the detector - uneven baseline, ghost peaks
4 s
The retention time of an analyte on a GC column was 5.0 min. The column efficiency according to this peak was 90,000 total theoretical plates. The peak had THIS width at the base
2.5
The retention time of ortho- and para- xylene isomers on a GC column were 10.6min and 11.1 min, respectively. Their widths at half height were 6.0s and 8.1s, respectively. From this, it can be concluded that the resolution b/w these two peaks had THIS value
2.53 x 10^-4 M
The solubility product constant for silver carbonate (Ag2CO3) has a value of 8.1 x 10^-12 (at 25oC). From this information it can be concluded that in an aqueous system, where solid silver carbonate is in equllibrium with its ions in saturated solution, the conc. of silver ions has THIS value
They differ signicantly
The titanium content (mg/g) in a steel sample was determined by two diff methods: (a)-atomic absorption spectrometry (AAS) and (b)-Inductively coupled plasma (ICP). The following results were obtained in replicate measurements: AAS: 4.70, 4.48, 4.63, 4.49, 4.82, 4.54, 4.77, 4.09 ICP: 5.29, 4.90, 4.89, 5.21, 4.86, 5.02 THIS conclusion can be drawn with regard to the means obtained by the two methods
One
The titration curve representing neutralization of a strong acid with a strong base contains THESE many inflection points
What is special about fluorescence /emission spectrophotometer?
There is a 90 degree angle bw entrance and exit slit to block source light.
reducing vs oxidizing agents
These are different than oxidizing agents and reducing agents. Agents are species that cause something to happen. So an oxidizing agent causes something else to get oxidized. To cause something else to lose electrons, it must gain electrons. Therefore, the oxidizing agent contains the element being reduced. This is another important distinction - individual atoms (elements) get oxidized or reduced. Agents are the entire compound containing the elements gaining or losing electrons.
James (martin and RLM synge)
This British scientist was not among those who shares the 1952 Nobel Prize in chemistry for their work in the field of chromatography
CZE
This analytical technique can separate only ionic species
Hydrogen
This carrier gas is most suitable for fast GC analysis
CZE
This does not represent a chromatographic technique
Purnell
This equation expresses resolution b/w a pair of chromatographic peaks through chromatographic characteristics of the second eluting peak
Helium
This gas is most commonly used as the mobile phase in GC
Wall-coated
This is the most widely used type of GC open tubular columns
3.079 x 10^10
This many molecules are present in 2.25 picogram of CO2
8.468 x 10^10
This many molecules are present in 2.25pg of methane
Adsorption
This phenomenon leads to the accumulation of solutes on the surface of a solid or liquid
1000nL
This represents a typical liquid sample volume for injection into a GC system
Sample
This represents small portion of population
Two-tailed F test
This significance test should be used to decide whether the precision of one method is significantly greater than that of the second method
Open tubular
This type of column is commonly used in GC
TC meaning and example
To contain, volumetric flask
Silanol groups
To deactivate a GC column, THESE fxnal groups on the fused silica capillary surface are chemically reacted with a suitable deactivating reagent
TD meaning and example
To deliver; buret
Effect is not signifanct
To investigate the effects of insoluble components on the determination of phosphorus in a detergent, 6 diff samples were analyzed by spectrophotometric method. Each sample was divided into two portions: one portion was filtered and the other was not. The rest of the analysis was identical for both portions of the sample. The results were as follows (mg/L) Filtered sample: 37.1, 26.4, 26.2, 33.2, 24.3 Unfiltered sample: 35.2, 26.0, 25.7, 32.8, 24.7 A paired t-test (P=0.05) will lead to THIS conclusion regarding the effect of filtering on the spectrophotometric results
None of the above
Total retention times for phenanthrene, anthracene, and chrysene eluted from a GC column were 5.3min, 5.7min, and 8.1 min respectively. Among these three analytes, THIS one spent more time in the mobile phase than the other two
adding an electrolyte can enhance the coagulation of colloidal suspension (T/F)
True
3.664
Two analytical methods (chromatographic method and spectrophotometric method) were used to analyze a test material. Replicate measurements were made by each of the two methods with the following results on analyte mean conc (mg/kg) and measurements S.D (mg/kg) Chromatographic: n=12, Mean=31.83, SD=0.424 Spectrophotometry: n=9, Mean=29.32, SD=0.648 THIS critical value of F should be used to perform a two-tailed F test on this data set at 95% confidence level
Random error
Uncontrollable parameters of an analytical measurement gives rise to THIS type of error
X ray fluorescence
Useful when sample cannot be put into sol'n
What does a monochromator do?
Uses diffraction (grating) to separate light so only one wavelength of light leaves through exit slit
Why do bands spread in chromatography?
We know that bands only get wider down the column, but why? (Notes: U = linear flow rate down column) 1. Longitudinal diffusion -molecules diffuse away from the center of the band, an inevitable process -the longer a solute spends in a column, the more time it has to diffuse down that column and the wider the peak it has -broadening due to linear diffusion is inversely related to flow rate: broadening = 1/U *meaning that the faster the flow rate, the less the solute diffuses and the narrower the band (and peak are) 2. Equilibration time -it takes time to equilibrate between the MP and the SP -- aka to reach equilibrium -the faster the MP moves, the broader the peak gets *the rate of mass transfer increases with temp. -here, broadening is directly proportional to flow rate of the MP (called broadening due to the finite rate of mass transfer) -solute requires a finite time to equilibrate between th emobile and stationary phases -- if equilibration is slow, solute in the stationary phase lags behind that in the mobile phase, thereby causing the band to spread -the slower the flow rate, the less the zone broadens due to this mechanism 3. Multiple pathways -independent of flow rate -occurs on a column/path that is packed with solid particles -some of the random flow paths are longer than others and some particles travel faster than others so this does not have to do with linear flow rate -the smaller the SP, the less this problem occurs because solute is having to move around SP particles
tr-tm. t'r.
What is the equation for the adjusted retention time? What is its symbol?
t'r/tm. k.
What is the equation for the retention factor? What is its symbol?
K x K' = 1
When a chemical reaction reaches equilibrium, the equilibrium constants of the forward reaction (K) and that of the reverse reaction (K') have the following relationship.
Random variation
When a null hypothesis is accepted, it signifies that the observed diff b/w the compared values is due to THIS
Buffer
When a weak acid is titrated with a strong base, this system is created
1000 times increase
When pH of a dilute solution is decreased from 5 to 2, its molar hydrogen ion conc undergoes THIS change
6.13g
a 250.00mL volume of 0.25M solution of sulfuric acid contains THIS many grams of H2SO4
matrix effect
a change in analytical signal caused by anything in the sample other than analyte
systematic/determinate error
a consistent error that can be detected and corrected
The Rate Theory explores why components may travel at "..." There are 3 examples; (3) The total "..." is equal to "..."
a different rate throughout the column -EDDY Diffusion (different rate along the cross section) -Diffusion (spreading) with and against the flow -The MASS TRANSFER between the phases is not instantaneous, dependent on diffusion in and out of the each phase column dispersivity the total of all 3 = A + B/u + Cu - VAN DEEMTER
INternal standard
a known amount of a reference species is added to: samples, standards and blanks -it is chemically and physically similar to the analyte
precision
a measure of how close a series of measurements are to one another -determined by replicates
titration curve
a plot of some function of analyte or titrant concentration vs titrant volume
back titration
a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution
Chromatography - Plate Theory The column is considered to contain "..." in which equilibrium of "..." occurs. For a gaussian peak, the width at half the maximum peak is reduced by 2 when N is increased by "..."
a series of discrete sections (theoretical plates) the analyte between the mobile and stationary phases 4
outlier
a significantly different value
ANOVA uses _____ test to determine whether there is or not a difference among the population means rather than pairwise comparisons like t test
a single
Standard
a solution of known concentration
electromagnetic radiation can be described as
a wave
relative error
absolute error divided by true value
Percent relative error
absolute error/expected times 100
percent relative uncertainty
absolute uncertainty/measured value x 100
Relative Uncertainty (re)
absolute uncertainty/value of measurement
every molecular species is capable of _____ its own frequencies of electromagnetic radiation
absorbing
the color of a solution is related to its
absorption spectrum
B (in van deemter Eq)
accounts for diffusion B= 2(gamma) Dm affected by temp, [ ], solubility, density, viscosity, gamma-- channel uniformity
C (in van deemter Eq)
accounts for equilibration Cs = f'(k') * (df^2/Ds) Cm = f(k') * (r^2/Dm)
A (in van deemter Eq)
accounts for path A=2(lambda)dp decrease particle diameter, increase speed of separation
A known amount of analyte is added to an aliquot of sample- accuracy or precision?
accuracy
Identical standards are analyzed by two different methods- accuracy or precision?
accuracy
Most common fuel for flame atomization
acetylene air
unbiased mean estimate
achieve if all members of the population have an equal probability of being included in sample
unbiased variance estimate
achieved if every possible sample is equally likely to be drawn
Anion-exchange SPE sorbents Extraction: Extraction of "..." analytes from aqueous matrix using "..." interactions PRIMARY AMINE for "..." QUARTERNARY AMINE for "..."
acidic anion exchange weak anion exchange strong ion exchange
indicators
added to analyte solution to produce an observable physical change, signaling end point at or near equivalence point
tr prime eqn provided symbols
adjusted retention time, where tm is time for mobile phase to move through column (no interaction)...just the amount of time solute interacts with stationary phase
Five types of chromatography
adsorption, partition, ion, size exclusion, and affinity
random error (indeterminate error)
affect measurement of precision and causes data to scatted around a mean value
systematic error (determinate error)
affects measurement of accuracy and causes mean to differ from true value
electrophoretic mobility
allows separation based on charge
LOQ
amount of analyte that can be measured with reasonable accuracy; yblank+10s to get SIGNAL
spectroscopic methods are based on measuring the
amount of radiation produced or absorbed by molecular or atomic species of interest
titration
an analytical method based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte
Sig figs MULT/DIVISION
answer will have same as number with fewest total sig figs
Sig figs ADD/SUBTRACTION
answer will have same number of sig figs past decimal point as the least in calculation (EX: 9+2.8=12 OR 7.528+ 6.0= 13.5)
Sig figs with add/sub and mult/division
apply in order of operation
deviations from beers law appear when abrosbing species undergoes ______, ______, or ____ with the solvent to give products that absorb differently from analyte
association, dissociation or reaction
AAS
atomic absorption spectra -light source is ONLY needed to absorption
AES
atomic emission spectra -NO LIGHT SOURCE NEEDED
Monochromator exit slit width determines
bandwidth (range of wavelengths allowed thru)
Cation-exchange SPE sorbents Extraction of "..." from aqueous matrix using "..." interactions. CARBOXYLIC ACID for "..." SULPHONIC ACID for "..."
bases cation exchange Weak cation exchange Strong cation exchange
Flame ionization detector
best for organic cmpds
dynamic range of flame AAS is better or worse than GFAAS and what is dynamic range
better, amount of linearity
the basic principle of ANOVA is to compare the ____ variation to the ____ variation
between the group within the group
With a nonpolar GC stationary phase, what determines elution time?
boiling point, the higher bp take longer to elute off
Molecular vs atomic absorption spectroscopy light source
broadband vs line sources....deuterium/tungsten VS hollow cathode lamp (HCL-cathode made of element you want to analyze)
What light source is used for molecular spectroscopy?
broadband, tungsten lamp (deuterium will cover UV part of UV-vis)
confidence intervals are broader when having a ____ sample
broader
how is surface absorption avoided in coprecipitation
by reprecipitation, the filtered solid is redissolved and reprecipitated
how is mixed crystal formation avoided in coprecipitation
by separating the interfering ion before the final precipitation step
how is occlusion, mechanical entrapment avoided in coprecipitation
by slow formation rate of precipitation and digestion
Light eqn
c=lambdav
Compare measured value to known value
calculate x+/- ts/sqroot(n) and find out if number is included in range OR solve t calculated by plugging in known (if t calc is larger than t table at 95%, they are statistically different)
a series of standard solutions of the analyte are used to construct a
calibration curve or working curve
randome errors are small errors that (can or cannot) be eliminated and detected
cannot
error in mismatched cells can be avoided by
carefully matched cells use or linear regression procedure
Plastic volumetric flask instead of glass
certain analytes won't adsorb to plastic
Affinity
chromatography where molecule in complex mixture becomes attached to stationary-covalently bound molecule (like an enzyme, substrate rxn)
Ion
chromatography where one type of ion is present in stationary phase to attract opp charge ions in solute of mobile phase
Size exclusion
chromatography where only small molecules can enter (like proteins)
Adsorption
chromatography where solute adsorbs directly to stationary phase surface
Partition
chromatography where solute dissolves in liquid layer of stationary phase
large values of relative supersaturation yield _____ precipitate
colloidal
Statistical significance: 3 cases
comparing measured with known/true value, comparing two diff methods, comparing differences of multiple samples and two or more methods
quantitative transfer
complete transfer of a solid - any residue remaining would causer error
Peak area is proportional to
concentration bw same samples
linear relationship in calibration curve is used to predict ____
concentration of analyte solution
according to beers law, absorbance is directily proportional to
concentration of the absorbing species and the path length of the absorbing medium
partition coefficient K
concentration on stationary/concentration in mobile phase
blanks
contains solvent or reagent but no analyte
How to find mass percentage/ppm given Molarity (moles/liters of solution)
convert moles to grams and then you pretty much have mass percent (because grams of chemical over 1000 grams of solution); the difference between ppm and mass percentage is 4 decimal points...example: 0.0855% is 855 ppm
small values of relative supersaturation yield _____ precipitate
crystalline
Does tr increase or decrease with increased temperature?
decrease
absorption transfers energy to the molecule and results in a ____ in intensity if electromagnetic radiation
decrease
When wavelength increases, frequency
decreases
as absorbance of solution increases, transmittance
decreases
as light traverses a medium containing an absorbing analyte, the intensity _______ as the analyte becomes excited
decreases
confidence interval ________ as measurement sample increases
decreases
decreasing S ________ the standard error of the mean and improves accuracy
decreases
the equivalent
definition varies from reaction to reaction
Confidence level
degree of certainty that true mean falls within confidence interval
Enthalpy symbol and meaning
delta H, heat of reaction
Entropy symbol and meaning
delta S, disorder of reaction
Gibbs free energy equation
deltaG= deltaH-tdeltaS
the response is the ______ variable in an ANOVA test
dependent
reduction potential > 0
desire for e-
reduction potential < 0
desire to lose e-
PMT is used for
detection of low intensity photons
F= 0.5
detector responds 1/2 as much to analyte than standard.
F=2
detector responds 2 times as much to analyte than standard.
F=1
detector responds the same to X & S
photomultiplier tube
detects single photon, is highly sensitive
What can cause band broadening in liquid chromatography?
dif path lengths, flow rate of mobile phase too slow or fast
error
difference between measured/experimental value and the true value
disadvantage of normality
different definitions for the equivalent
beers law described absorption behavior only of ______ solutions
dilute
All chromatography depends on a compound being "...", and is all based on different "..." The partition coefficient K(d) = "..." If K(d) is large, then "..."
distributed between two phases phase equilibria (Eqm.concentration of A in solvent 1) /(Eqm.concentration of A in solvent 2) A will concentrate in solvent 1
Double beam spectrophotometer advantages (3)
do not have to swap out blank and sample, accounts for drift in source intensity/detector, chopper allows for throughput of several spectra/second
different compounds have different responses in a particular detector - same amount of two compounds "..." Can be overcome by using "..." Calculated by repeated injection of mixture containing equal amounts of the compounds to be analysed. One is chosen as a reference and "...." An alternative is to use an "..." method
doesn't mean same area RESPONSE FACTORS all other peak areas referred to this internal standard
colloidal solution particles dont merge together or form bigger particles due to
double ionic layer formation
3 temperature stages of graphite furnace
dry (solvent), char (atomize), atomize (ground state atoms)
Three heating phases of graphite furnace for AAS
dry (solvent), char (vaporize), atomize (make ground state atoms)
electron capture detector
e- emitted from Ni, analyter accepts e-, decreased current works well for halogens, organometallics, and nitriles very sensitive
Usually use "capillary columns". The stationary phase is coated onto the inside of a long (25 - 200 m) tube with a narrow bore which has 3 benefits "..."
efficiency and speed, less sample needed
amplitude
electric or magnetic field strength at a maximum of a wave -height
__________________ is a form of energy that is transmitted through space at enormous velocities
electromagnetic radiation
Advantages of double beam scanning spectrophotometer (3)
eliminates need to swap out sample/reference, accounts for "drift" in source intensity/detection, chopper allows for speedy analysis (several spectra/sec)
Delta H positive, reaction is ____ and heat acts as a
endothermic, reactant
random/Indeterminate Error
equal probability of a measurement being high or low
______ is when stoichiometrically equivalent amounts of analyte and titrant are present _______ is when the observable physical change signals the above
equivalence point end point
equivalent in precipitation and complex formation reactions
equivalent weight is that weight which reacts with or provides one mole of reacting cation if it is univalent one half mole if divalent, one third if trivalent, etc
equivalent in oxidation/reduction reactions
equivalent weight is the amount that directly or indirectly produces or consumes 1 mol of electrons
Chemiluminescence spectroscopy refers to
excitation of the analyte by a chemical reaction
Delta H negative, reaction is ____ and heat acts as a
exothermic, product
normality N
expresses a solution concentration -number of equivalents of solute in 1L solution
concentration
expresses the composition of a solution with respect to its volume
3. Ion-Exchange SPE Application: Sorbent ("..."): Interactions: Eluents:
extraction of ionic analytes from polar samples ion-exchange particles silica gel or polymers containing cation or anion functional groups cation and anion exchange buffers, salt solution
2. Reversed-Phase SPE Application: Sorbent ("..."): Interactions: Eluents("..."):
extraction of non-polar analytes from polar samples (e.g. water) hydrophobic particles; bonded-phase silica, copolymers (C18-bonded phase (Octadecyl-) Silica) nonpolar interactions (van der Waal's forces) nonpolar solvents; hexane, ethyl acetate, acetone but also methanol, acetonitrile
1. Normal-Phase SPE Application: "..." Sorbent ("..."): Interactions: Eluents:
extraction of polar analytes from non-polar samples (e.g. oil) polar particles; activated alumina, silica gels polar interactions (hydrogen bonding, dipole-dipole) polar solvents
type II error also known as
false negative
type I error is also known as
false positive
least squares method is used to
find mathematical equation for calibration function
Pros of flame AAS vs GFAAS
flame is faster, has better reproducibility, better dynamic range, and can be used for BOTH AAS and AES
The van deemter equation is the summation of various powers of "...", these powers are "..."
flow speed -1, 0, 1
Boltzmann distribution tells you what
fraction of atoms excited at certain temp
transmittance T
fraction of incident light that passes through a sample
energy of a photon is proportional to its
frequency
Preparing solution. Method 1
from a solid -based on the concentration and volume of solution you want, figure out the amount of solid needed -dissolve with the solvent to make up to the desired volume
the order of state in decreasing free rotation is
gas > liquid > polar
Difference bw gas and liquid chromatography
gas vs liquid mobile phase
name of graph that shows normal distribution
gaussian curve
alpha is always
greater than 1
Photodiode array (PDA)
has an elliptical mirrow and polychromator??? what used for?
t test is used when
having two data sets or sample is too small
_____ removes the solvent and any volatile species carried down with the precipitate
heating
NP-HPLC, the mobile phase generally consists of "..." Deactivators include "..."
hexane mixed with other organic miscible solvents water, alcohols
_____ molar absorbptivities are desirable for quantitative analysis because they lead to high analytical sensitivity
high
the stimulus causes some of the analyte species to undergo a transition to a _______ energy or ________ state
higher excited
for UV and visible radiation, excitation occurs when an electron in low energy molecular or atomic orbital is promoted to a
higher energy orbital
partition coefficient is a measure of what
how much solute interacts with stationary phase (large K means it likes to interact with stationary phase)
concentration
how much solute is contained in a given volume or mass of a solution or solvent
Standard Addition
ideal for analyzing sample in a complex matrix; add known standard to constant amount of sample; x-int =[sample]
spectrum gives information on the analytes
identity and concentration
Mobile phase additives: small % of additives or modifiers added to mobile phase to "..." (2)
improve peak shapes, retention times and to modify selectivity
decreasing S _________ precision
improves
None of the above
in a In a GC run, phenanthrene peak was eluted at 10.0min, the peak width at the base being 6 s. The number of theoretical plates generated by the used column was THIS
Questions to practice from textbook
in email attachment
aqueous
in water
how to solve systematic error
increase sample size
the factor is the ____ variable in an ANOVA test
independent
ICP stands for and is used for? 2 advantages
inductively coupled plasma, atomization/excitation with fewer molecular interferences and SIMULTANEOUS MULTI-ELEMENT analysis
vibration of chemical bounds is induced by which radiation
infrared radiation
spectroscopy
interactions of radiation and matter
tr is larger when solute...
interacts more strongly with stationary phase
Buffers - are required in "..." and sometimes in "..." The chosen pH of the buffer must be "..." of the compounds of interest in order to get the vast majority of the molecules "..." Volatile buffers are needed for: "..."
ion-exchange chromatography reversed-phase chromatography (RP chromatography) two units apart from the pKa in one single form Light scattering detection Coupling with mass spectrometry
HPLC involves what kind of interaction with solid phase
irreversible adsorption
hypothesis testing is used to
judge whether a numerical difference is a result of a real difference or a consequence of the random errors in all measurements
Boltzman symbols
k is constant provided, gs are number of ground states (degeneracies), delta E is energy dif between states, T is temp (+273.15), Ns are numbers of atoms in each state * is excited, 0 is ground
retention factor (k) related to partition coefficient K how?
k=K(vs/vm)
wavelength
lambda
_____ particles are generally desirable for gravimetric work
large
gross error
leads to outliers and is caused by humans. It can be detected statistically
Very narrow exit slits cause
less absorbance
the size of a colloidal precipitate is
less than 10 ^ -4 cm
How do instruments differ between AAS and AES
light source for absorption but not emission
Transmittance eqn
light that passes through sample/light that passes through blank p/p0
wavelength
linear distance between successive maxima or minima of a wave
residual is used to evaluate
linearity of the calibration curve
supernatant liquid
liquid above a pack solid
for an analyte solution the _____ the path length of light, the ______ absorbers are in the path and the ________ the attenuation
longer more greater
Broadening caused by mobile phase being too slow
longitudinal broadening
prior to applying the stimulus, the analyte is predominantly in its _________ energy or ______ state
lowest ground state
solvent
major species used to dissolve the minor (solute)
ppm
mass of analyte/mass of sample*10^6
ppb
mass of analyte/mass of sample*10^9
gravimetric titration
mass of titrant is measured rather than the volume
emission spectroscopy refers to
methods in which the stimulus is heat or electrical energy
paired data is used to
minimize sources of variability that are not of interest
Box car average
minimizes distance between data points and best fit line/ minimizes standard deviation
solute
minor species in solution
Deactivators ("...") - a substance added to the mobile phase to "..."
moderators deactivate the most highly adsorptive centres of the stationary phase
the _____ is the SI unit for the amount of a chemical substance
mole
How do molecular/atomic spectra differ?
molecular has broader peaks due to vibrational energy of bonds
Difference bw molecular and atomic spectra
molecular has wider bands, atomic is small line
Broadband light source used for? What kind of bulbs?
molecular spectroscopy, deuterium/tungsten for UV-Vis
Molality (m)
moles of solute/kg of solvent
Molarity (M)
moles of solute/liters of solution
molality
moles/kg solution -m
beers law applies only when measurements are made with
monochromatic source radiation
Example of a wavelength selector
monochromator
What uses grating/dispersion?
monochromator
When wavelength decreases, there is more or less energy?
more
Pros of GFAAS vs flame AAS
more sensitive (in optical path longer), less sample required, can analyze solids
ANOVA allows comparisons between
more than two population means
4. Mixed-mode SPE sorbents -have "..." that exploit "..." OCTADECYL AND QUATERNARY AMINE for "..." OCTADECYL AND PRIMARY AMINE for "..."
multiple retentive sites on an individual particle different retention mechanisms Non-polar and strong anion exchange non-polar and weak anion exchange interactions
pooled standard deviation is used when
neither is more than twice that of the other
Diffraction angle eqn (may have to do inverse of d at end)
nlambda=d(sinincoming+sinleaving) n is order diffraction d is distance between lines
Liquid chromatography
no terms eliminated
thermal conductivity detector
non destructive, but not sensitive
Reverse phase HPLC
nonpolar stationary, increasingly polar mobile phase
If deltaG is positive, the reaction is
nonspontaneous
Two types of phases for HPLC
normal and reverse
Gaussian distribution relies on
normal distribution, with random error, assumes weird u and o (population) not sample
coprecipitation
normally soluble compounds carried out of solution by a precipitate
precipitates are formed by (2 ways)
nucleation and particle growth
type II error
null hypothesis is accepted when false
type I error
null hypothesis is rejected when it is true
Sig fig inverse log
number of digits past decimal point in power it is raised to=total number of digits after decimal point in answer (EX: 10^1.26 = 18)
frequency
number of oscillations in a second
Sig figs log
number of total sig figs in log(x)=number of digits after decimal point in answer (EX: 8.4 x 10^5 = 5.92)
wavenumber
number of waves per cm. reciprocal of wavelength
Absolute error
observed minus expected
Fluorescence
occurs when LUMO--> HOMO releases energy; generally occurs in rigid molecules
ORGANIC SOLVENT-WATER PARTITION COEFFICIENT (P)- ratio of the concentration of "...." it is a measure of "..."
of unionised compound X in organic solvent (e.g. octanol, chloroform) to the concentration of compound X in water Hydrophobicity and hydrophilicity of chemicals
equivalent in neutralization reactions
one equivalent weight is the amount of substance that reacts with or supplies 1 mol of hydrogen ions in that reaction
spectrochemical methods that use visible, UV and IR radtiation are called
optical methods
Review polyatomic ion charges
other quizlet
intermediate form of diprotic acids
pH = 1/2 (pk1 + pk2) -regardless of formal concentration -and at high enough concentration, everything will have = pH regarless of concentration
another deviation from beers law is if the cells holding the analyte and blank solutions are not of equal ____ and equivalent ______ ____
path length and optical characteristics
What can be used to detect low intensity photons?
photomultiplier tube (PMT)
How does a PMT work?
photon hits cathode, causing electron to eject. electron attracted to dynode 1, which causes more electrons to eject (electron cascade), current measured at anode
How does PMT work?
photon hits cathode, which ejects e-, e- is attracted to dynode, causes ejection of more e-, current measured
With a polar GC stationary phase, what determines elution time?
polarity, most polar molecules interact strongly and elute last
weird u
population mean
weird o
population standard deviation
colloidal precipitates - digestion
precipitate is heated in the solution from which it was formed and allowed to stand in contact with solution
Aliquots from a blood sample are sent to 3 separate laboratories for analysis using same method
precision
Five aliquots of the same sample are injected for a gas chromatographic analysis by one person on same day
precision
Standard deviation is related to
precision
population standard deviation is a measure of
precision
significance level
probability of a result to lie outside the confidence interval
peptization of colloids
process by which a coagulated colloid reverts to its original dispersed state -washing is needed -risk of losses if pure water is used
sampling
process to obtain a representative fraction
What does the light source in a spectrophotometer do?
provide wavelength of light needed for absorption
Analytical chemistry
provides the tools to make qualitative and quantitative measurements of components in complex samples
Total charge
q = nNF where q = electric charge; n = electron charge in balanced reaction; N = moles of molecule; and F = faraday constant which is C/moles
chemical stoichiometry
quantitative relationship among amounts of chemical
stray radiation or stray light is
radiation from the instrument that is outside the nominal wavelength bond chosen for determination
random sample
randomization procedure is applied
confidence interval for the mean (Cl)
range of values within which the population mean lies with a certain probability
What is bandwidth in spectrophotometry and what determines it?
range of wavelengths allowed thru exit slit, determined by width of exit slit
precipitating reagent - specific
react only with single chemical species, rare
precipitating reagent- selective
react with a limited number of species, more common
standard solution
reagent of known concentration
calibration
relationship between analytical response and analyte concentration. -requires purifying agents and standardized methods
alpha with t eqn provided
relative retention (separation factor of peaks)
particle size is related to the _____________ of the solution
relative supersaturation
non-radiative relaxation
relaxing to the lowest vibrational level of LUMO = fast
standard error of the mean
represents the sample mean deviation from the actual mean population
IR spectroscopy
responds to change in dipole moment
Raman
responds to change in polarizability
Propagation of Error: Mult/Division
same as propagation of error with addition/subtraction but instead of adding sqs of error and taking sq root, you add percent relative uncertainties, squared under square root
Molecular absorption vs atomic absorption method
same but atomic needs to be atomized and uses line sources of light (narrow, correct frequency) from DIFFERENT HOLLOW CATHODE LAMPS (made of element you are looking for)
when to run with internal standards for calibration curve
sample introduction or instrument response varies
correct response is
sample response - blank response
replicates
samples of same size analyzed the exact same way. Allow for estimation of uncertainty
the most difficult step in the entire analytical process and the step that limits the accuracy of the procedure
sampling
stray light is the result of
scattering and reflection off surfaces of gratings, lenses or mirrors and windows
a material or solution whose concentration is determined from the stoichiometry of its reaction with a pure standard material
secondary standard
serial dilution
series of concentrations of standard solutions
external standard calibration
series of standard solutions is prepared separately from the samples
Lab notebook
should be written so that it is understandable by a stranger
Jablonski Diagram
shows movement from ground state to excited state
gross sample
similar chemical composition and in particle size distribution
when to use simple calibration curve
simple or well understood matrix
calibrations sensitivity is the _____ of the curve
slope -it does not indicate what concentration differences can be detected
Sensitivity
slope, steeper/bigger slope means more sensitivity
residual is more close to actual value when is is a _____ value
small
sample standard deviation S is used for
small data sets (<20)
energy differences among rotational energy states are _____ than those among vibrational states
smaller
the differences in energy among the vibrational states are ______ than among electronic states
smaller
particle size of silica particles in HPLC column affects resolution how?
smaller particles increases resolution because it makes a smaller plate height
LOD
smallest quantity of analyte that is significantly different than the blank; yblank+3s to get SIGNAL
GC - stationary phases - early stationary phases were "..." but these "..." Most stationary phases in use today are based on "..." Different substituents are used to "..."
solids such as silica or alumina can be reactive and change the sample silicone polymers vary the properties of the stationary phase.
the molar concentration is the number of moles of a species in 1L of the _______________
solution
Broadening caused by mobile phase being too fast
some solute remains behind because it did not have time to equilibrate
modern instrumental methods
spectroscopic, electrochemical chromatographic & electrophoretic
results of spectroscopic measurements are expressed by a _____, which is a plot of emitted or absorbed radiation as a function of frequency, wavelength or wavenumber
spectrum
If deltaG is negative, the reaction is
spontaneous
Propagation of Error: Addition and Subtraction
sq root of the terms each squared and added (EX: +/- 0.3, +/- 0.01... square each one, add, square root
confidence interval for sample includes the ______ in contrast to the confidence interval for population
square root of the N samples
precision is described by
standard deviation, variance and coefficient of determination (deviation from the mean)
reagent
standard solution of a chemical substance
If you are getting bad peaks in GC, what can you change theoretically? What are you most likely to try first?
stationary phase or temperature. temperature programming
What can you change to get better peaks in HPLC? Which are you more likely to change
stationary phase polarity or mobile phase. mobile phase
What factors affect GC separation?
stationary phase properties and temperature
Gradient elution
strength (polarity) is ramped up over time
the higher the concentration of absorbers the ________ the attenuation
stronger
Cross-linked polystyrene is formed as a result of copolymerisation of "..." The amount of "..." added for the reaction determines the "..." It is stable at pH "..." It can be microporous or contain a mixture of micro- and macropores: meaning "..."
styrene and divinylbenzene divinylbenzene degree of cross-linking and hence the pore structure 1-13 meaning it can be selective of shape
Internal calibration
substance similar to analyte (ie deuterated); used to normalize signal by reducing random error
ORGANIC SOLVENT-WATER DISTRIBUTION COEFFICIENT (D)- ratio of the "..." D = logP = logD at any pH for "..." logK(ow) =
sum of the concentrations of all forms (ionised and un-ionised) of the compound X in organic solvent (e.g. octanol, chloroform) in each of the two phases [X(organic)]/[X(un-ionised]*[X(ionised)] unionisable compounds octanol-water partition coefficient
Separation of basic compounds in RP-HPLC: To avoid interaction of basic molecules with "..." groups "..." should be used But to separate bases, "..." mobile phase has to be used So another base (alkylamine or alkaline buffer) can be added to "..."
surface silanol acidic eluent neutral or alkaline block silanol groups
slurry
suspention of solid & liquid
error that has a definite value, cause, sign and leads to bias
systematic error
when standard deviation is unknown we use ___ instead of ____
t instead z
Monochromator does what?
takes polychromatic (many wavelength) and allows passage of one wavelength thru exit slit (by using grating to manipulate light DISPERSION)
capacity factor (k')
tells efficiency of a separation k'= time in SP /time for MP to elute= mol SP/mol MP
null hypothesis assumes
that the numerical quantities being compared are the same at a certain significance level
Solid-phase extraction - mechanism Sorption of analytes from solution on solid phase based on "..."
the affinity of analytes for the solid phase
equivalence point
the amount of added standard reagent is equivalent to amount of analyte
absorption law tells us quantitively how
the amount of attenuation depends on the concentration of the absorbing molecules and the path length over which absorption occurs
Precipitation gravimetry
the analyte is separated from a solution of the sample as a precipitate and it is converted to a compound of known composition that can be weighed
volatilization gravimetry
the analyte is separated from other constituents of a sample by conversion to a gas of known chemical composition. The weight of this gas then serves as a measure of the analyte concentration.
analytical sensitivity is the ratio of
the calibration curve slope to the standard deviation
Variable UV-Vis detector allows for "..." Photo Diode Array detector allows for "..." Application: Compounds that "..." Due to small number of molecules which "..."
the choice of one wavelength in order to accommodate the absorption characteristics of a particular solute or group of solutes Allows for an access to all of the wavelengths simultaneously Fluorescence or of which fluorescing derivatives can be obtained Show fluorescence, this type of detection can be used for the detection of trace quantities of analyte in complex matrices
accuracy
the closeness of a measured value to the true value -expressed by absolute or relative error
linear dynamic range
the concentration range over which the analyte can be determined using a linear calibration curve -large LDR desirable
we get info about the analyte measured by measuring:
the electromagnetic radiation emitted when returning to ground state or the amount of electromagnetic radiation absorbed when excited
Photoluminescence spectroscopy
the emission of photons is measured following absorption
Detection limit
the lowest concentration that can be reported with a certain level of confidence
absorption spectroscopy
the measurement of the amount of light absorbed by a compound as a function of the wavelength
solution
the mixture of solute and solvent
Mobile phase regimes: Isocratic - "..." or "..."
the mobile phase remains constant over the course of the separation Gradient - alteration of the composition of the mobile phase during the course of the chromatographic run
end point
the point in a titration at which an indicator changes color
confidence level (Cl)
the probability for the true mean to lie within a certain interval
Variance (s^2)
the square of the standard deviation
CHEMICALLY MODIFIED SILICA Silanol groups on "..." are chemically modified to give stationary phases with "..." ie. non-endcapped silica have "..."
the surface of silica specific properties additional selection properties from the silanol interactions
confidence limits
the upper and lower limits of the interval
f test compares
the variance of two data sets and more than two means
Gas chromotography can be useful as a large range of samples can be analysed as long as "..." Uses "..." as the mobile phase and "..." as the stationary phase The samples are separated by "..." (2) Qualitative analysis - Quantitative analysis -
they are volatile and stable inert gas a variety of solid or liquid coated solid 1) their boiling points 2) how they interact with the stationary phase in the column -Usually by comparison with known standards. Can be done by GC - Mass Spectrometry -Measurement of peak areas and calibration.
period P
time in seconds for maxima or minima to pass a point in space
Retention time, tr has two contributions: (2) what relationship do these 3 retention times have?
tm - the time taken for an unretained compound t'r - the time the solute molecules spend retained by the S-phase t'r = tr - tm
TC
to contain -burets
TD
to deliver -pipettes
Extraction has 3 core principles;
to present samples directly to the chromatographic system to increase the concentration of analytes in the extract to remove potentially interfering matrix compounds (particularly important for GC, LC/MS)
electronic transitions are
transitions between two different orbitals
double beam scanning spectrophotometer alternatively measures ____ through ___ or _____
transmittance through sample (p) or reference (p0)
electromagnetic radiation does not require a
transmitting medium
primary standard
ultrapure compound that serves as the reference material for a titration -high purity -stable -modest cost solubility in titration medium -large molar mass
Propagation of uncertainty final
uncertainty should have one less sig fig past decimal point than the sig figs past decimal point in result
Dalton
unit expressing biological macromolecules
_____ is often used for homogeneous generation of OH ion
urea
Convert ylod or yloq to concentration
use calibration curve ylod or yloq=m(concentration)+b
External calibration
use standard solutions spanning a range of conc, measure response
Case 3: Comparing diff of mult samples analyzed with two methods
use t calc equation with d, if t calc is larger than t table at 95%, they are statistically different
Comparing two data sets, mean values
use t calc equation with s pooled, still if t calc is larger than t table at 95%, they are statistically different
Fcalc
used to compare precision (s2)^2/(s1)^2 (should always be >1) Fcalc> Ftable -- different precision
Photodiode Array (PDA)
uses polychromator and curved mirror, as well as an array (like a microarray)
IR generally is not energetic enough to cause electronic transitions but it can induce transitions in ______ and _____ states
vibrational and rotational
d-->d absorb
visible light (transition metals)
vol%
volume of analyte/volume of total solution*100
RP-HPLC, Mobile phases: generally consist of mixtures of "..." with various "..." End capping "..." peak definition
water or aqueous buffer solutions water-miscible organic solvents improves
when to use standard additions for calibration curve
when the matrix affects analytical signal
When to use AES instead of AAS
when you need a better LOD (same reason as fluorescence, compare one little light against dark instead of diff between flame and light generated by excited photons) OR when you don't know what elements you are looking for (because it can be multi-element and simultaneous)
Wide vs narrow bandwidth
wider bandwidth is less sharp peaks, narrow is less absorbance
z
x-mean/stdev
Grubbs test (Gcalc)
|Q-xavg|/s > Gtable, reject value Used to define outliers
proteins absorb at
~ 280 nm (bc of aromatic R groups)
sigma--> sigma* absorbs at
~100nm
"Quality of separation" is determined by two things Quality of Separation can be increased by:
• Relative retentions - efficient chromatography • Peak widths - efficient columns • Increasing the separation of the peaks • Minimising the peak spreading
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