CHEM 113 - FINAL REVIEW
Given the results of an EDTA titration, be able to calculate water hardness in units of ppm CaCO3
(2.0x10^-4 M)(# of drops) = Molarity of Divalent Cations (Molarity of Divalent Cations)(100 g CaCO3/ 1 mole)(1000 mg CaCO3/ 1 g CaCO3)= Hardness (ppm CaCO3)
Know how to convert ppm Ca2+/Mg2+ as determined by AA analysis to ppm CaCO3
(Ppm Ca^2+)(100.04 g CaCO3/1 mole)(1 mole/ 40.08 g Ca^2+) = ppm CaCO3 (Ppm Mg^2+)(100.04 g CaCO3/ 1 mole)(1 mole/ 24.3g Mg^2+) = ppm CaCO3
Understand lab notebook guidelines and apply the guidelines to their own notebooks
- First two pages are for table of contents ( date, title, page #) - must use ink, n pencil or whiteout - to cross out do one single line (no scribbling) - Record all data and observations DIRECTLY into notebook - handwriting should be readable -make sure to get notebook signed after the end of the period. - no white line spaces - name, date, partner on every page - reference the CHEMTREK book - descriptive titles and headings - missing units
State the relationship between ΔG and Keq.
- if delta G is negative and the value of K is high, the reaction is spontaneous - if delta G is positive and teh value of K is low, the reaction is spontaneous in opposite direction - if delta G is 0 nd value of K is close to 1, the system is at equilibrium
Use good graphing techniques to construct a calibration graph in Excel.
- title should be in Y vs. X form - axis labels should include units - use scatter plot without line connectors, then add trend-line - data should not be cluttered, extend axis - include line of best-fit on graph
Be able to do problems of this type: Fig 14.2 shows titration curves of a strong, monoprotic acid titrated with 0.10 M NaOH (aq) solution. Calculate the concentration (M) of the acid given: o Curve A = 25.00 mL unknown acid o Curve B = 5.00 mL unknown acid o Curve C = 10 mL unknown acid o Curve D = 25 mL unknown acid
A: (.1M x 8.5 mL) / 25mL = 0.03 M B: (.1M x 20.5 mL)/ 5mL = 0.4 M C: (.1M x 34 mL) / 10 mL = 0.3 M D: (.1M x 45.5mL) / 25 mL= 0.2 M
Explain the differences in what is measured by AA, EDTA, and TDS. Be able to apply this knowledge to analyze experimental results.
AA spec. Only measures Ca^+ and Mg^2+ divalent cations. EDTA measures all divalent cations. TDS isn't a good hardness measure because it doesn't detect specific contaminants in water. therefore AA is the more accurate from the three.
Explain how an acid-base indicator works and be able to choose an appropriate acid-base indicator for a titration.
Acid/ base indicators are weak bases or acids. They have a special characteristic that the color of the indicator is different when the indicator is dissociated vs. when the color is non dissociated. - strong acid/strong base titration: use the phenolphthalein indicator because its colorless at pH <8.3. You can get away with using any indicator though. - strong acid/weak base titration: methyl orange indicator because it will become red at the end point. - strong base/ weak acid titration: use phenolphthalein indicator because it reaches the violet color at the end point.
Identify an acid, base, conjugate acid, and conjugate base in an acid-base reaction.
Acid: a molecule that can donate a proton or accept an electron pair Base: reacts with acids to form salts, they accept H protons from acids Conjugate acids: the chemical compound of the base with the donated H proton conjugate bases: the chemical compound of the acid after donating it's proton (the acid minus one H)
Explain the difference between weak/strong acids and weak/strong bases. This includes an understanding of Ka, pKa, Kb, and pKb.
Acids: Weak - partially dissociate into one in aq solutions -pH is not as low as the strong acids -acid dissociation constant is lower value -doesn't release all H ions -pka is a larger value Strong -completely dissociate into their ions in aq solutions -pH is very low , the stronger = the lower -acid dissociation constant is a higher value -releases all H ions in solution -pka is a small value Bases: Weak -partially dissociate into hydroxyl ion and cation -partially dissociate into iono -ph is greater than 7 but lower than 14 -less reactive -pKb is high Strong -completely dissociate it's cation and hydroxyl ion in aq solution -dissociate ions almost 100% -pH is closer to 14 -highly reactive -pKb is almost 0
Given data similar to Section D, be able to determine activation energy by plotting/graphing this data.
Arrhenius Equation- k=Ae^(Ea/RT) -Ea- activation energy (kJ mol^-) -R- gas constant -T- abs. Temperature (K) -A- frequency factor
Define key terms from the background reading Atoms- Conductors- Insulators- Semiconductor- Electric current Direct current- Alternating current- Ohm's law- Voltage- Current- resistance- Power- Electronic circuit- Carbon film resistor- Digital multimeter-
Atoms- negatively charged electrons and positively charged protons Conductors- solids that have many free electrons that can be easily pushed through the structure. Insulators- nonmetallic solids that don't conduct electricity because the electrons are in fixed positions Semiconductor- solids that have intermediate electrical conductivity that can be controlled to any desired level Electric current- the flow of charge through a substance Direct current- current that flows in only one direction Alternating current- current that flows in both directions Ohm's law- V=IR Voltage- electrical pressure/ force that pushes charge Current- quantity of electrons passing through a point in a second (measured in amperes) resistance- (in Om's) what goes against the current Power- P=VI Electronic circuit- range net of electrical materials that allow a current to flow Carbon film resistor- depositing a carbon film on a small ceramic cylinder. The color bands correspond to the band numbers. Digital multimeter- quantitative measurement of V, I and R (instrument)
Balance redox reactions.
Cancel out e^- and spectator ions
If given ΔH, ΔS and T for a reaction, be able to calculate ΔG and determine if the reaction is spontaneous under those conditions.
Delta G = delta H - T(delta S) Delta G is positive = non spontaneous Delta G is negative = spontaneous
Define "brine".
Brine is the name given to a concentrated solution of salt in water (salt water).
Identify/define Brønsted-Lowry acids and bases.
Brønsted-Lowry acids donates its proton and as the transfer happens, the bond to the donor breaks. Brønsted-Lowry base acts as a proton acceptor because it accepts hydrogen ions that are donated from the acid.
Define buffer solution and identify examples of buffer solutions.
Buffer solutions is the solution that if an acid or base were to be added to it, the pH would remained unchanged. Examples: Acetic acid, sodium acetate, ammonia and ammonium chloride
Know the basic electrochemistry terms and be able to apply them to a given cell: voltaic cell, electrolytic cell, anode, cathode, oxidation, reduction, oxidizing agent, reducing agent. Know the signs (+/-) at the anode and cathode for both types of cells
Cathode + Anode -
If you were given results for experiments similar to Section B, C, and D, be able to explain the color changes of the indicators and identify the cathode, anode, and the redox reaction involved.
Cathode- electrode where reduction takes place Anode- electrode where oxidation takes place Redox reaction- the two half reactions (Red and Ox) combined Color changes- caused by dissociation of the H^+ ion from the indicator itself
Given a list of indicators with their pH ranges, be able to select the appropriate indicator for a titration and explain your choice.
Choose an indicator whose pH range falls writhing the pH change of teh reaction.
Define "direct current" and "alternating current"
DC- current moving in one direction AC- current moving in both directions
Define "activation energy" and understand the relationship between activation energy and reaction rate.
Ea- rate determining step, the energy needed in order for the reactants to react to their transition state. The higher the Ea, the slower the reaction rate,and vice versa.
Balance a redox equation similar to those given in Expt 9 and the background.
Easy
Assign oxidation states to each element in a given reaction.
Easy.
Draw potential energy diagrams for endothermic and exothermic reactions.
Easy.... Endo- products higher than reactants Exo- products lower than reactants
Understand the trends in properties that the halogen family exhibits (examples: melting point, atomic radius, electronegativity).
Electronegativity: F>Cl>Br>I : decrease as you go down the halogen column Melting points: Increase as you go down halogen column Atomic radius: increases going down the column
Be able to calculate the molarity of a solution if given the mass of solute and volume of the solution.
Equation: Molarity = mol/L Convert the given mass of solute into mol, then divide this number by the given volume (convert to L if necessary)
Determine if the following statements about a chemical reaction/process are True or False. Correct statements that are false by changing the latter half (about spontaneity and T) of each statement o If ΔH is negative and ΔS is negative, the reaction is spontaneous at any T o If ΔH is negative and ΔS is positive, the reaction is spontaneous at any T o If ΔH is positive and ΔS is negative, the reaction is non-spontaneous at any T o If ΔH is positive and ΔS is positive, the reaction is spontaneous at any T
Equation: delta G = delta H -T(delta S) 1. False, only at low temperatures 2. True 3. True 4. False, only at high temperatures
Be able to solve calorimetry problems such as: 0.100g Urea was dissolved in water to make 50.1 g of solution. During the dissolution the water temperature rose to 28.7 oC from 23.5 oC. Assuming the heat capacity of the solution is 4.184 J/(g⸳K): -Is the dissolution exothermic or endothermic? -Calculate ΔH for the dissolution
Equation: q=mCs(delta T) m= 50.1 g Cs= 4.184 J/gK T= 278.35 K q= 58347 J = 5.83x10^4 J = q surrounding ===> -5.83x10^4 J = q system Equation 2: delta H = q system / moles of urea dissolved Delta H = (-5.83x10^4 J)/ (0.100g/60.06 g/mol) = -97 J/mol Since delta H is negative, this means the dissolution is exothermic with a delta H of -97 J/mol
Identify and locate all common lab supplies in the lab room
Eyewash fountain, first aid kit, safety shower, fire extinguisher, fire blanket, personal vent, fume hoods, exits, spill-kit station.
Know the electron configurations for the halogens.
F- 1s(2)2s(2)2p(5) Cl- 1s(2)2s(2)2p(6)3s(2)3p(5) Br- 1s(2)2s(2)2p(6)3s(2)3p(6)4s(2)3d(10)4p(5) I- 1s(2)2s(2)2p(6)3s(2)3p(6)4s(2)3d(10)4p(6)5s(2)4d(10)5p(5) At- 1s(2)2s(2)2p(6)3s(2)3p(6)4s(2)3d(10)4p(6)5s(2)4d(10)5p(6)6s(2)4f(14)5d(10)6p(5)
Given the information in Table 5.1 be able to determine the resistance of a particular resistor and whether an experimental measurement is within tolerance.
First band = first digit, second band = second digit, third number = the exponent (x 10^ ). The fourth band gives the accuracy of the resistance.
Know the names and atomic symbols for the halogens.
Fluorine - F Chlorine- Cl Iodine- I Bromine- Br Astatine- At Tennessine- Ts
Explain why there is a progression from gas to solid going down the column.
From the top to bottom, electronegativities of the halogens decrease. This means that the forces between the elements increase (going down the column) and this results in a higher boiling point as you go down.
Compare paper, liquid, and gas chromatography. How are they alike and how do they differ?
GC- the flowing / mobile phase is a gas LC- the flowing / mobile phase is a liquid They all aim to separate mixtures by using solvent on filter paper.
Be able to explain chromatography in general terms and be able to explain gas chromatography -Be able to identify/explain the different types of mobile and stationary phases
GC- the process of separating compounds in a mixture by injecting a gaseous/ liquid sample into a mobile phase. It separates the chemical components of a sample mixture, then detects them to determine their presence and how much of it is present. Mobile phase are either liquid or gas. Stationary phases are solid or liquid supported on a solid.
Define key terms from the background reading Gas chromatography- Detectors- Detector output (signal) Retention time(tr) Retention time of air- Beilstein detector- Electron capture detector
Gas chromatography- technique for separation of volatile substances by percolating a sample mixture in a gaseous mobile phase through a porous stationary phase contained in a long tube Detectors- thermal conductivity (TCD), flame ionization (FIDD), electron capture (ECD) Detector output (signal)- usually fed to a strip chart recorder or to a dedicated computer Retention time(tr)-the time that elapses between. The injection of the sample and when the center of the component band is detected by the detector Retention time of air- the time between sample injection and the detected air peak Beilstein detector- sensitive, selective GC detector that emits visible light when separated halocarbon components go through it Electron capture detector- the detector attached to the GC
Calculate the pH (using the Henderson-Hasselbalch equation) for a buffer solution.
H.H equation PH = pKa + log (ln^-/Hln)
Define key terms from the background reading Halides Chlorofluorocarbons
Halides- when a halogen gains one electron (F^-, Cl^-,Br^-,I^-) Chlorofluorocarbons- Freon are nontoxic, inert, and nonflammable. Used for heat transfer fluids in refrigerators and AC.
Explain why halogens are so reactive.
Halogens are so reactive because they readily gain an electron to fill their outermost shell.
Describe what is meant by hard water
Hard water means that there is a lard COMBINED concentration of Ca^2+ and Mg^2+
Define key terms from the background reading Hardness Total dissolved solids (TDS) Atomic Absorption Spectrophotometry (AA) Beer-Lambert Law:
Hardness- determined by the presence of the dissolved divalent cations (Ca^2+ and Mg^2+) Total dissolved solids (TDS)- the amount of residue left after the evaporation of a known volume of water Atomic Absorption Spectrophotometry (AA) - useful technique for the determination of metals that are dissolved or suspended in a solution Beer-Lambert Law: It=Io(10^-abc) -Io - intensity of the initial light source
Be able to interpret reaction profiles.
Identify from the graph: Ea, Reactants, Products, change in energy
State the relationship between ΔG, ΔH, and ΔS.
If delta G is negative (spontaneous) : - delta H is exothermic (negative) - delta S increases in disorder (positive) If delta G is positive (no spontaneous): - delta H is endothermic (positive ) - delta S decreases in disorder (negative)
Explain the relationship between ΔG and spontaneity.
If delta G is negative, it will be favorable for spontaneity If delta G is positive it will be less favorable for spontaneity
Explain why the equivalence point is acidic, basic, or neutral for the above titrations and be able to choose an appropriate indicator for these titrations.
If equivalence point is... 1. Below 7 = most likely acidic 2. At 7= neutral 3. Above 7= most likely basic
Use Le Châtlier's principle to explain how adding acid or base to a weak acid indicator will shift the equilibrium.
If we add base, we shift the equilibrium towards the yellow form . If we add acid, we shift the equilibrium towards the red orange form.
Determine the Ka and pKa of a weak acid from its titration curve with a strong base
In titration curve, the pH = pKa at the equivalence point of the graph. To obtain the Ka value, simply use the formula PKa = -log(Ka)
Determine the order of reaction for a rate law expression, e.g., for the reaction 2A + B → 3 C the rate law is rate = [A][B]2 .What is the overall order of the reaction? What is the order with respect to the individual reactants?
Overall order - third order A is in first order B is in second order
Know the biological relevance of buffers.
It's an organic substance that has a neutralizing effect on hydrogen ions. It maintains the body at the correct pH so that processes continue to run optimally.
Explain the Beer-Lambert Law and its significance in AA analysis.
It=Io(10^-abc) - It: transmitted intensity - Io: intensity of initial light source The significance is that the intensity of signal (decrease) is proportional to metal concentration in sample
Calculate Ka from pKa (and vice versa) and calculate pH from [H+ ] (and vice versa).
Ka= (A^-)(H^+)/(HA) A^- - concentration of conjugate base of acid H^+ - concentration of hydrogen ions HA - concentration of chemical species HA pKa= -log(Ka)
Be able to write the equilibrium constant expression (Keq) for a given reaction or process
Keq= [(C)^x(D)^y] / [(A)^x(B)^y] - A&B: the reactants - C&D: the products -x&y: the number of moles of each reactant or product
Write the equilibrium constant expression for the dissolution of a solid in water
Ksp = urea (s) —> urea (aq)
Understand the relationship between Eo cell, K, and spontaneity for a given reaction.
Large E cell means a large equilibrium constant, which means a spontaneous redox reaction Small E cell means a smaller equilibrium constant, which means a non spontaneous redox reaction
Know the different parts and function of the homemade GC we made (draw a sketch)
Latex tubing connecting the Bunsen burner to the glass tubing. The glass tubing contains the tide detergent and polyester fiber on both ends. Latex tubing is connected to the other end that is connected to the L-shaped tube. The L-shaped tube is connected to a wire that is coiled very tightly. This wire coil is where the flame comes up from. Two cloth pins are placed on both ends of the glass column to assure balance.
Sketch the gas chromatograph used in this experiment and label the most important parts (Hint: look at the diagram on page 19-12).
Latex tubing connecting the Bunsen burner to the glass tubing. The glass tubing contains the tide detergent and polyester fiber on both ends. Latex tubing is connected to the other end that is connected to the L-shaped tube. The L-shaped tube is connected to a wire that is coiled very tightly. This wire coil is where the flame comes up from. Two cloth pins are placed on both ends of the glass column to assure balance.
Define key terms from the background reading Le Chaterlier's principle- Equilibrium process - Equilibrium - Ion-product constant of water (Kw) pH scale- Acid Dissocaition Constant (Ka) - Monophonic acids- Buffer solution- Buffering action- Buffer capacity-
Le Chaterlier's principle- if an equilibrium is upset, the system responds in a direction that will reestablish equilibrium. Equilibrium process - proton transfer Equilibrium - when the rate forward reaction is equal to the rate of the reverse reaction Ion-product constant of water (Kw) - equal to 1x10^-14 M = [H3O^+][OH^-] pH scale- proton concentrations that are worked in a logarithmic scale Acid Dissocaition Constant (Ka) - the expression for the equilibrium constant for acid hydrolysis Monophonic acids- acids that have been capable of donating one proton Buffer solution- consist of either a weak acid combined with the salt of its conjugate base or weak base combined with the salt of its conjugate acid Buffering action- the process of which they resist pH change when a strong acid/base is added, it adjusts equilibrium Buffer capacity- amount of strong acid or base that can be added before the pH of the solution changes
Know the values for the following SI unit prefixes: M, k, d, c, m, µ, and n.
M- mega (10^6) k- kilo (10^3) d- deci (10^-1) c- centi (10^-2) m- milli (10^-3) mu- micro (10^-6) n- nano (10^-9)
List some uses of gas chromatography.
Miscellaneous analysis of foods Pollutants Dairy product analysis- rancidity Inorganic compound analysis
Be able to explain the difference between the original gas thermometer and the modified gas thermometer. How did adding water to the bulb of the pipet change how the thermometer worked? Which is more accurate? Which has a larger range? Be able to explain what causes the differences in accuracy and range.
Mod. Gas thermometer Pros- larger temp. Range, environmentally safe (no mercury), quicker response Cons- less sensitive to temp change (less accurate ) Gas thermometer Pros- more sensitive to temp change (more accurate) Cons- smaller range Adding water to the bulb extended the range because there is less gas to expand, which means it is also less temp sensitive
Given the Eo cell value for a reaction, be able to calculate the reduction potential for one of the half cells. Also, know how to write a balanced redox equation for the spontaneous reaction between two half cells.
Nernst Equation: Log(K) = nEo / 0.0592 E= Eo - (RT/nF)lnQ Eo = standard potential Q= reaction quotient F= faraday constant n= # of moles of e^- R= gas constant T= abs. Temp
Know how to use the Nernst equation to calculate Ecell and understand what happens to Ecell as concentrations of the ions in solution change (like when a battery "runs down").
Nernst Equation: Log(K) = nEo / 0.0592 E= Eo - (RT/nF)lnQ Eo = standard potential Q= reaction quotient F= faraday constant n= # of moles of e^- R= gas constant T= abs. Temp It shifts towards the right towards the products or shifts to the left towards the reactants
Be able to identify the variables in Ohm's law and the units associated with each variable.
Ohm's Law - V=IR. V= voltage (V) I= current (A) R= resistance (ohms)
Understand how the Henderson-Hasselbalch equation is derived from the equilibrium expression, 𝐾𝑎 = [𝐻+][𝐴 −] [𝐻𝐴] , for a weak acid. Note: this derivation is given in Section C, step 5.
Only focused on the ratio of (A^-/HA), then take the log base of that and add the pKa to get the pH.
Identify oxidation and reduction half-reactions as well as the oxidizing and reducing agents
Ox: Fe^2+ —-> Fe^3+ +e^- Red: Ce^4+ +e^- —> Ce^3+ Overall: Fe^2+ + Ce^4+ —> Fe^3+ + Ce^3+ Red agent: Fe^2+ Ox agent: Ce^4+
Identify two types of columns used in GC and explain how they differ
Packed columns - short, thick columns -Produce broad peak shapes -Low separation performances -handle large sample volumes Capillary columns -produce sharp peak shapes -achieve excellent separation performance -suited to higher-sensitivity analysis
Explain (in a few sentences) how we made a lead acid battery in Expt 15 part E.
Placed two lead strips into a tray that had 1M H2SO4 solution in it. Then to charge the Pb-acid battery, I clipped the leads to the 9V battery to each strip of the Pb for about a minute. Unclipped the battery and examined he lead strips.
Identify and locate all lab safety equipment in the lab room.
Plastic rulers, plastic magnifier, sheet protectors, 24 well tray, thin stem pipes, plastic straw, matches, scissors, pH paper, distilled and ethyl alcohol in squirt bottles, aluminum foil, personal waste container
Balance redox equations.
Put half redox reactions next to each other and multiply which ever equation so that all e^- cancel out (as well as spectator ions) so that youre left with the reducing and oxidizing agent
List the four major factors that determine the rate of a reaction.
Rate depends on: - temp of a system -concentrations of various chem species present -presence of a catalyst -rate at which reactants can mix/diffuse together
List the major factors that determine the rate of a reaction and be able to apply this to experimental conditions. (i.e., what could be done to speed up/slow down a reaction?)
Rate depends on: - temp of a system -concentrations of various chem species present -presence of a catalyst -rate at which reactants can mix/diffuse together To speed up - increase temp, add catalyst Slow down- decrease temp, no catalyst
Explain how the rate law or activation energy for a reaction is determined experimentally.
Rate law is determined using the method of initial rates. Ea is determined graphically, it is the distance from Reactants to transition state(the peak).
Be able to define "rate law" and explain how it is determined experimentally. Be able to calculate the rate law using experimental data.
Rate law- the rate at which chem reaction depends on reactant concentration Rate= k(A)^x(B)^y
Define the mechanism or a reaction and the term "rate-determining step"
Rate-determining step: the largest, longest Ea step from the diagram. The rate-determining step is the longest Ea because it is the slowest rate at which the reaction undergoes.
Define key terms from the background reading. Redox reactions- Half reactions: Reduction Oxidation- Spectator ions- Spontaneous reaction- Electrochemistry - Electrochemical cells- Half-cells- Anode Cathode- Half cell potentials- Standard Hydrogen Electrode (SHE)- Salt bridge- Voltaic cell (battery) Electrolysis cell
Redox reactions- reactions in which there are changes in oxidation numbers Half reactions: half of the redox reaction, be being the gain of electrons and the other being the loss of e^- Reduction- gain of electrons Oxidation- loss of electrons Spectator ions- ions that remain unchanged , basically cancel out in half reactions Spontaneous reaction- redox reactions in which reactants are observed to react and produce products Electrochemistry - study of redox reactions that either produce or utilize electrical energy Electrochemical cells- electrical energy (moving e^- or ions) in devices, the two Half cells combined Half-cells- each contain a metal electrode in contact with its own metal ion Anode- electrode at which oxidation takes place Cathode- electrode at which reduction takes place Half cell potentials- force of the sum of so potentials Standard Hydrogen Electrode (SHE)- the universal reference electrode Salt bridge- the connection between both half-cells Voltaic cell (battery)- electrochemical cell in which a spontaneous redox reaction can occur Electrolysis cell - electrochemical cell in which non spontaneous redox reaction is made to occur by means of an external power
Define key terms from the background reading. Spontaneous process- Non-spontaneous process- Equilibrium constant (Ksp) - Enthalpy (delta H) - positive: - negative: Gibbs Free Energy (delta G). - positive: -negative: Entropy (S) Entropy (delta S). - positive: - negative:
Spontaneous process- will occur under a specific set of conditions Non-spontaneous process- will not occur under a specific set of conditions Equilibrium constant (Ksp) - the equilibrium reaction/ process occurring in the saturated solution Enthalpy (delta H) - the exchanged heat between a system and its surroundings at constant pressure - positive: reaction is endothermic, taking heat from surroundings - negative: reaction is exothermic, giving heat to the surroundings Gibbs Free Energy (delta G) - indicates the spontaneity of a reaction. - positive: the products have more energy, are less stable, and less likely to exist than reactants, the reaction is non spontaneous -negative: the products have less energy, more stable, and more likely to exist than the reactants, the reaction is spontaneous Entropy (S) - measure of how spread out or dispersed the systems energy is Entropy (delta S) - change in entropy during the reaction or process. - positive: the number of ways to disperse the energy of the system increases during a reaction - negative: the number of ways to disperse the energy of the system decreases during a reaction
Explain the differences between stationary and mobile phases and the purpose of each.
Stationary - doesn't move with the sample - acts as a constraint on many components in a mixture, slowing them down to move slower than the mobile phase Mobile- moves with the sample -propels a substance through a structure, which holds the station phase,enabling chromatographic separation to occur
Explain how a Beilstein detector works, including what it detects the presence of.
The B.D. Consists of a copper wire coil that's placed in a small flame generated at the column ext by burning natural gas. The B.D. Detects the compounds containing halogen atoms.
Describe the color change that occurs when a halogen, such as I2, reacts with starch/KI and explain what the iodide is converted to in this reaction.
The color change turns from a brown color to a deep blue color when the I2 (iodine) binds inside the pores of the helix shape. The Iodide (I^-) is the converted when the I2 is broken and creating the Iodine ions.
Write the dissociation reactions for mono or polyprotic acids or bases.
The dissociation reactions for acids or bases is when there are no more H protons to work with from the acid
Locate the buffer region and the equivalence point on a titration curve.
The equilvalence point is the most vertical point in the titration curve (kind of half of the vertical line). the buffer region is the pH value at half the distance to the equivalence point (in x axis).
Explain the purpose of a salt bridge.
The purpose of the salt bridge allows for electrical neutrality to be maintained in each half cell. The bridge allows the flow of cations and anions to either half cell solution.
Understand the importance/meaning of reduction and oxidation potentials - specifically, what the magnitude of the value indicates.
The redox potentials are the measurement of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode. It provides quick and easy characterization of the degreee of reduction in a chem reaction. Redox potential is positive and large = ability to oxidize is enhanced Redox potential is negative and large = reducing ability is enhanced
Why did we need standard data (provided by the stockroom technicians) as part of our AA analysis? How did we use this data? What is a calibration?
The standards are of known concentrations and are used to calibrate the instruments and make the calibration graph.
Define key terms from the background reading Thermodynamic- Kinetics- Rate Rate depends on: Mechanism- Rate Law- First order Second order Overall order of reaction Arrhenius Equation- the system-
Thermodynamic- the study of initial and final states of a chemical system Kinetics- the study of the arrows factors that control the rates of a reactions Rate- how the concentration of reactant or product changes over time Rate depends on: - temp of a system -concentrations of various chem species present -presence of a catalyst -rate at which reactants can mix/diffuse together Mechanism- all of the actual elementary steps involving molecules that take place simultaneously/consecutively. And that add together to give the observed, overall reaction Rate Law- Rate= k(A)^x(B)^y -k : rate constant -A&B: the reactants -x&y: the concentrations (the # in front of the reactants) First order- exponent = 1 Second order - exponent = 2 Overall order of reaction = addition of exponents Arrhenius Equation- k=Ae^(Ea/RT) -Ea- activation energy (kJ mol^-) -R- gas constant -T- abs. Temperature (K) -A- frequency factor the system- series of reactions
Know the relationship between thermodynamics (exothermic/endothermic) and kinetics (rate of reaction)
Thermodynamics and kinetics have no relationship. Thermo. - overall properties, behavior, and equilibrium imposition of a system Kinetics - rate at which a Particular process will occur and the pathway by which it will occur
Understand how the concentrations of species in solution change during the course of titration (as monitored by pH or conductivity).
They change because of the strong base or acid. They don't change when a buffer solution is involved .
Know that AA is normally used to analyze water for specific metals.
To analyze water for a metal
Perform and analyze an acid-base titration
To perform the acid base titration in exp. 1 you simply add indicator to the # of wells needed. The indicator doesn't change the pH, it simply tells you which well is the pH of the solution when the solution changes from one color to a different one. Serial titration is when you add the acidic solution into each well (first well = one drop, second well= two drops. Etc...) and the numbered well that the color changes is the given pH.
Prepare a solution of a specified concentration
To prepare a solution of the specified concentration of NaCl (0.015M) in 100mL.First use the formula Molality= mol/L to get the number of moles — 0.0015mol. Then you have to obtain the molecular mass of NaCl —58.44 g/mol and use the formula mol=g/mol to solve for the grams (0.08766grams). To prepare a solution of the specified concentration 0.015M, you will need 0.08766 grams of NaCl in 100mL solution.
Properly dispose of chemical waste
To properly dispose of chemical waste, use waste containers for waste liquids. Then transfer your waste container to the fume hoods and empty out in the PRIMARY waste container (jugs).
Define the term "Total Dissolved Solids" and explain the differences between the information obtained by TDS analysis compared to "Divalent Cation Analysis"
Total dissolved solids (TDS)- the amount of residue left after the evaporation of a known volume of water. This analysis allows an assessment to be made of the potential scaling problem of a water sample. Divalent cation analysis: quantitative analysis of a water sample that can conveniently be Carried out by means of a complex action titration. Referred to as water hardness.
Explain what London dispersion forces are and how they relate to molecular size/weight
Types of forces acting between atoms and molecules that are normally symmetric (they have dipoles) Larger and heavier atoms exhibit stronger dispersion forces. - the valence electrons are farther from the nuclei, they aren't as tightly pact and can temporarily be.dipoled Smaller and lighter atoms exhibit weaker dispersion forces. - valence electrons are more tightly pact because they are closer to the nuclei, they have a harder time becoming temporary dipoles.
Explain in a short paragraph how an AA analysis is carried out, and the principles behind it.
Used to determine chemical elements using the absorption of light by free atoms in the gaseous state. A sample is aspirated into a flame that contains the metal ions from the sample. A light is shown through the flaming lamp and flirt is absorbed by matching the delta E. the non absorbed light bounces off a mirror, onto the metal grating where it is analyzed by the photomultiplier tube.
Understand the equation below 𝑯𝑫𝟐− + 𝑴𝒈𝟐+ + 𝑪𝒂𝟐+ → 𝑴𝒈𝑫− + 𝑯+ + 𝑪𝒂𝟐+ (𝑬𝑫𝑻𝑨 →) 𝑪𝒂𝑬𝑫𝑻𝑨 +𝑴𝒈𝑬𝑫𝑻𝑨 + 𝑯𝑫𝟐− Blue Red 1st. 2nd. last - blue
Used to determine water hardness using EDTA titration
Explain how retention time can be predicted in GC. Explain using IMFs
Using the example from EXP> 19, Freon 123 had a higher molecular weight, therefore it had a longer tension time. Freon 22 had a lower molecular weight, therefor had a shorter retention time. Retention can be predicted in GC by looking at the molecular size of the atoms, the bigger their size, the stronger the IMF's are, the stronger the IMF's , the longer the retention time. Retention time= the time from injection to detection.
Know how to use Ohm's Law to calculate current, resistance, and voltage for simple circuits.
V=IR
Explain the difference between voltaic and electrolytic cells.
Voltaic and electrolytic cells are opposites of one another. Voltaic cells convert chemical to electoral energy through an oxidation-reduction reaction. Electrolytic cells convert electrical to chemical energy.
Define water hardness and list two problems caused by hard water.
Water hardness- the amount of dissolved calcium and magnesium in the water. Problem one - reacts with cleaning products, creating a soap buildup Problem two -causes dry skin and dry hair after bathing because it prevents the soap from lathering to skin.
Be able to explain the chemistry behind the EDTA titrations. Why do we need the buffer? Why do we spike the samples with MgEDTA? Write the reactions to help explain.
We need the buffer because it avoids the pH to change. The spike is to ensure that there's enough Mg to do the titration. 𝑯𝑫𝟐− + 𝑴𝒈𝟐+ + 𝑪𝒂𝟐+ → 𝑴𝒈𝑫− + 𝑯+ + 𝑪𝒂𝟐+ (𝑬𝑫𝑻𝑨 →) 𝑪𝒂𝑬𝑫𝑻𝑨 +𝑴𝒈𝑬𝑫𝑻𝑨 + 𝑯𝑫𝟐− Blue Red 1st. 2nd. last - blue
Explain how dilution affects the pH of a buffer as well as the buffer capacity
When a solution is diluted, the pH will remain the same, buffers resist pH change.
Understand the relationship between the equilibrium constant and the spontaneity of a reaction.
When the equilibrium constant is... 1. Greater than 1 = a spontaneous reaction 2. Less than 1 = non spontaneous reaction
Sketch the titration curve for X M HCl titrated with Y M NaOH. Be able to label the axes correctly, identify pH at the beginning of the titration (before NaOH added), the volume of NaOH added at the equivalence point, and the pH at the equivalence point.
Y axis: pH X axis: mL of .100M NaOH added to 50 mL of .100 M HCl Ph at beginning: 1 Volume of NaOH at equiv point: 50 PH at the equiv point: 7
Define pH and to interpret titration curves and locate important points (equivalence point, half-equivalence point, pKa).
pH is the measure of how acidic or basic a substance or solution is. PH of 0 indicates acidic and pH of 14 indicates basic, the pH of 7 acts as the threshold from acids to bases. The equilivanlence point from a a titration graph is where the curve is most vertical. The half- equivalence point is half the distance (x direction) from the equilvalence point. The pKa of a curve is the equivalence point.
Be able to calculate the amount of heat generated by a reaction based on the temperature change of the surroundings of the reaction.
q=mCs(delta t) -q: heat gained/lost by the surroundings -Cs: 4.18 J/gK -delta T: change in Temp (K)
Determine what will happen to the rate if the concentrations are changed, e.g., for the reaction 2A + B → 3 C the rate law is rate = [A][B]2 . What will happen to the rate if the concentration of A is kept the same and the concentration of B is tripled?
the rate will be multiplied 9 times because 3B^2 = 9B.
Explain the purpose of the standards that are run as part of AA analysis.
the standards give a better sense of the instruments accuracy (usually around 7/10 of a ppm) Accuracy of AA is much less than what's listed by the number of digits on the computer screen
Be able to interpret chromatograms and determine which peak corresponds to particular components if given formulas/structures.
tr= retention time to maximum color, Wb= difference in time between appearance and disappearance of colored flame, x-axis= time, y-axis= intensity of green color