CH 455 exam 1

what indicator will you be using for the purposes of this experiment- EDTA

EBT for Ca and Mg... Murexide for Ca

why do we use EBT as an indicator? what does the end point signify?

EBT is selective for Mg and endpoint tell total hardness

why do we use buffers for the titrations- EDTA

EDTA titrations have clearer endpoints (due to larger formation constants) at higher pH values.

describe the detector used in this experiment (GC)

Flame ionization detector—burns organic sample—make ions—current measured

describe how you will construct your calibration curve (HPLC)

From dilutions from a supplied standard stock solution

what is the primary reason to use HPLC instead of GC

HPLC can analyze non- volatile materials

what is joule heating (CE)

Heating that occurs within the solution bc of the motion created by charge carriers

describe the components of the GC instrument

Helium carrier gas, injector, column inside oven, detector

what two types of injection methods will you use today? describe how each of them works (CE)

Hydrodynamic (pressure sucking)// and electrokinetic (charge dif)

does EDTA bind equally to Ca and Mg? which has the higher complex ion formation constant

No- Kf around 10 for Ca... Kf for mg around 10^9. EDTA has a higher complex ion formation constant with Ca

what is the standard potential- CV

Potential we use to compare everything else to

what are the major components of an HPLC system and what is the function of each

Pump - forces mobile phase through at a specific flow rate Injector - injects sample into flow stream of mobile phase Column - separates the sample components of interest Detector - detects individual molecules that elute from the column Computer - determines time of elution

define spike recovery and explain why we use it in this lab (HPLC)

Spike recovery is a known quantity of analyte added to a sample to test whether the response to the sample is the same as that expected from a calibration curve

based on the structures of capsaicin and diyhydrocapsaicin, which will elute first and why (HPLC)

There is a soluble bond in the dihydrocapsaicin so it will come off first

describe how the detector used in this experiment works (HPLC)

UV visible detector- detects absorption of light. (aromatic ring can be detectible w UV vis)

conjugate base

a base that forms when an acid loses a proton... formate

what does a CV for a reversible reaction look like

a duck

chelating ligand

a ligand having more than one atom with a lone pair that can be used to bond to a metal ion.

what should potassium cyanide never come in contact with

anything near u

why do we use potentiometric titration for this experiment instead of just using an indicator

bc we are doing a precise measurement of pH—so the ability to take a first and second derivative to see inflection point is better

explain how determining the fist and second derivative will aid you in finding the experimental endpoints

better job at finding the peak- better inflection point

masking agent- EDTA

chemical that can be added to the sample solution to prevent the interfering ions from binding with EDTA, allowing it to complex the analytes.

how will you know when you have reached the titration endpoint- EDTA

color change

what is the function of counter electrode

controls for potential

define elctroosmotic flow (CE)

due to plug flow. any molecule will follow the flow of ions/ analytes

purpose of EDTA lab

figure out Ca and Mg ions in water

Define electrophoretic flow

flow occurs from attraction from opposite charges

what are the three ionization steps of phosphoric acid

h3po4 -> h2po4-, hpo4-2, po4-3

what is a polyprotic acid

has more than 1 proton

which gas is used as the carrier gas (GC)

helium

why is EDTA chosen for this titration

it is good at complexing (high K value)

how might the mobile phase be modified to provide greater separation of the two peaks (HPLC)

make the particle sizes smaller

how many endpoints will you observe in the experiment (potentiometric titration)

only 2 because the third dissociation is so strong that hydroxide is not able to remove proton

what does a pH meter measure

pH

define weak acid

partially ionized in aqueous solution

how does a pH meter work

pourus glass and known concentration of acid sitting inside the inner container of the pH meter and unknown amount outside—depending on the difference—u look at electro chemical potential difference of inside to outside.

what are the electrodes in a three- electrode cell?

reference, working, counter

why do we use murexide as the indicator for the second set of titrations

specificity for calcium

what are the characteristics of a good reference electrode?

stability and not easily polarizable

how do we vary the applied potential in a chronoamperometry experiment

stop function charge

solubility product

the constant for the equilibrium expression representing the dissolving of an ionic solid in water

when the reaction begins, how does the current change

the current increases

what is reverse phase HPLC

the stationary phase is non polar and the liquid phase (solvent) is polar.

describe what is happening chemically at each of the endpoints

the stronger acid protons fall off and at the second endpoint, the second proton of the triprotic acid falls off.

why dont we measure the water hardness of distilled water

there arent any metal ions in there

how will you know when you reached the first and second endpoints

there will be a steep climb in pH

complexometric titration

titration based on complex formation with metal ion

what is the purpose of the supporting electrolyte and what are you using in this experiment? (CV)

to minimize migration

where should u dispose of used filters and SPE cartridges (HPLC)

trash

why is all glassware acid washed- EDTA

we are looking for metal ions that easily attach to glass—acid wash to remove all lewis acid

what dont we calibrate the pH meters?

we are only interested in the differences in pH

is EDTA a strong acid or weak acid

weak hexodente ligand- hexoprotic acid (it can bind 6 times, forming a coordination complex)

when would you use a masking agent? -EDTA

when there can be an interfering ion

what is the function of working electrode

where potential change happens

what is the function of reference electrode

working against comparison

what process is responsible for the shape of the chronoamperometry curve after the potential step

Diffusion process as u watch a return back down because u see a slowing down in current generated as current

why do multidente ligands form more stable metal complexes than similar monodente ligands

it is much more thermodynamically stable (greater increase in entropy from binding 6 molecules as opposed to binding one)

what color will your solution be at the first endpoint? the second endpoint?

no color because we are not adding an indicator

what is normal phase HPLC

polar stationary phase and nonpolar liquid phase (solvent)

when a substance is being reduced, what type of current is produced

positve

conjugate acid with example

product that is different from a base by one proton... formic acid

what are the three acid dissociation constants and/or pka values for phosphoric acid

2,7,12

how many endpoints would expect to observe in the titration of a tripotic acid with a strong base

3 points

how many deprotonations need to occur in order for EDTA to effectively bind to a metal?

5 or 6

how many pka values does EDTA have

6

which metal ion must be present in the water for a color change to be produced and constant-EDTA

?

how do we vary the applied potential in a CV experiment

???

how are we eliminated electromigration and convection in this experiment

Adding potassium chloride salt/// convection by not stirring

why cant the hot sauce be injected directly into the instrument (HPLC)

Because the amount of particles traveling through must be minimized to prevent clogging. Also remove dissolved gases

what property of the compounds in this experiment determines their elution order (GC)

Boiling point

how does your internal standard make your analysis more accurate (GC)

By using an internal standard we can make sure that the prep work that precedes it is done in exactly same way

define pH

-log[H+]

how do you convert from the standard potential to the potential vs. the Ag/ AgCl electrode

.197 (add this to silver silver chloride electrode)

what is your internal standard (GC)

1-butanol

what metal ions are you going to test for in your experiment- EDTA

Ca and Mg ions

what metal ions generally contribute to water hardness-EDTA

Ca and Mg ions

what causes water hardness in nature?

Ca ion and Mg ion that form with hydroxides

what are the health hazards of capsaicins (HPLC)

Can burn mucous membranes and cause heartburn

how can you determine the water hardness due to calcium and magnesium individually

Can determine individual hardness of calcium by using murexide/NaCl compound which ONLY binds calcium, and EBT binds both Mg and Ca. We can subtract the hardness of Ca (murexide) from the total hardness (EBT)

what are some advantages for using a GC

Cheap and easy/ provides high resolution

what are some of the parameters that can be adjusted to achieve better separation (GC)

Choice of temp on the column—this is why we can vary the temperature.

Define gas chromatography

Chromatography w gas as mobile phase

define strong acid

Completely ionized in aqueous solution

by which three methods can an ion in solution reach an electrode surface

Convection, migration, diffusion

explain electrophoretic mobility (CE)

Every different chemical molecule has size and charge—and ability to move thru buffered soln .. small things high charge are more mobile

why are we increasing the temperature during a sample run (GC)

Increase temp bc higher BP would never come off... if we did really high then everything would come off... this is why some people use a temperature gradient.

formation constant

K value associated with ligand complexing with lewis acid

explain the internal standard method (GC)

Known amount of 1-butanol and know exactly its concentration—u can measure its response... quick way to calibrate

what type of molecules/ chemicals/ compounds are best suited for separation by CE

Mc that are not volatile/ dissolve in water/ dif in polarity and shape.. pretty much any kind can be separated

what is the purpose of CV experiment

Measure different coefficients for ferri to ferro... follow formation of interesting products by irreversible CV reaction thr-> tyr

which metal ion must be present in the water for a color change to be produced and observed- EDTA

Mg ion

what must u do to your sample before injecting it into the HPLC

Must run thru solid phase extraction

explain what a response factor is and how it is used in to calculate the concentrations of the compounds in this experiment (GC)

Response factor is a absorptivity factor In beers law—the multiplier for the relationship between concentration and the standard and the signal detected by flame ionization detector.

what can you tell me about the properties of each phase in reverse phase HPLC? relate this to stationary phase and mobile phase composition

Reverse phase has a nonpolar stationary and polar solvent Eluent strength is increased by making the mobile phase more like the stationary phase

how would the CV shapes differ for reversible and irreversible reactions

Reversible look like duck// irreversible look like dead duck

how are the components separated while passing through the column (GC)

Separated bc at any given temp- their likelihood of condensing down onto the stationary phase is dependent upon the type of molecule that it is... by varying temp u can get things off column

water hardness

The amount of dissolved calcium and magnesium in the water

describe how you will determine the concentrations of the mixture of two acids by a single titration

The first endpoint represents = amount NaOH required to remove all protons from HCl and one proton from H3PO4. The second end point= amount NaOH required to remove one more proton from H2PO4-. o Subtract amount NaOH at first endpoint from second endpoint -> concentration of H2PO4- could be determined. oSubtract moles H2PO4- from the moles of total acid calculated from the concentration of NaOH at the first endpoint.

describe how to use the solid phase extraction (SPE) (HPLC)

The sample is passed through the cartridge containing a hydrophobic stationary phase. Many of the components in the sample matrix, including the capsaicinoid analytes will be retained. This will then be washed out by eluting methanol and 1% acetic acid solution.

what reference electrode is being used... what is its reduction potential? CV

The silver- silver chloride electrode... .13 V difference