CHEM 272 Exam 2

Experiment 6: Intro to Titrations

two scenarios in which titrations are used

1. titrant is unknown (conc), analyte is know

2. titrant is known, analyte is unknow

Experiment 6: Intro to Titrations

two scenarios in which titrations are used

1. titrant is unknown (conc), analyte is know

2. titrant is known, analyte is unknow

what is it called when an analyte is known?

primary standard

using titration to calculate molarity

M: moles solute/L solution (volume delivered)

need to figure out what you don’t know from moles that you do know

2 strategies to monitor progress of titration:

1. pH monitoring with pH probe (potentiometric titration)

2. color change with pH indicator (endpoint titration)

what happens when there’s a 1:1 buffer

• pH=pka

• moles A- = moles HA

equivalence point

• moles titrant=moles analyte

• point of max slope on graph of volume of titrant v.s. pH

½ equivalence point

pH=pka

first derivative

total pH/ total volume

endpoint

where color change occurs

zwitterionic

has both a positive and negative charge that has a net neutral charge

how are peptide bonds formed?

hydrolysis reaction between the carboxylic acid of one r group and the amino acid group of the other

pKas in an amino acid

• carboxylic acids are 2

• amino groups are 9

• R groups vary

You will be analyzing a series of amino acid titration curves resulting from a new protein supplement. The goal is to determine whether the supplement is safe for those who are diagnosed with phenylketonuria. Which amino acid will you be looking for in your samples? 

phenylalanine

Experiment 7

standard reduction potential

a reducing agent’s ability to donate electrons

signs of oxidation

• gain bonds to oxygen

• lose bonds to hydrogen

• gain a double bond

• lose electrons

signs of reduction

• gain hydrogen

• lose bonds to oxygen

• gain electrons

• lose double bonds

active ingredient versus excipients

active ingredient: therapeutic affect

excipients: inert (bulking, color, preservatives)

back titration

indirectly quantifying analyte

what color does I^-₃ produce?

blue black

what color does I^- produce?

colorless

Which of the following species is the primary standard? 

ascorbic acid

iodate

thiosulfate

iodate

Which of the following species is the titrant in the standardization titration?

Group of answer choices

ascorbic acid

iodate

thiosulfate

triiodide

thiosulfate

Which of the following species is the analyte in the ascorbic acid titration?

Group of answer choices

ascorbic acid

iodate

thiosulfate

triiodide

triiodide because it is a back titration

experiment 9

cell potential equation

Ecell=Ecathode-Eanode

If E is +:

If E is -:

spontaneous, nonspontaneous

voltaic (galvanic) cell

spontaneous, generates voltage

electrolytic cell

nonspontaneous, needs voltage

experiment 10: thermodynamics

total system + total surrounding= 0

system: reactions

surroundings: everything else (universe)

1st law of thermodynamics

energy of universe is constant

2nd law of thermodynamics

dispersal of energy (entropy) in universe is always increasing

if delta G is negative

if delta G is positive

• reactant have more energy than products, rxn is spontaneous, exergonic

• reactants have less energy than products, rxn is nonspontaneous (endergonic), energy required

K>Q

rxn shifts towards products

K<Q

rxn shifts towards reactants

K and Q

product/reactant

Reaction Coupling

nonspontaneous rxn paired with spontaneous rxn

1. chemical processes

2. redox processes→ electron flow → generate electrons

biochemical standard state

• temperature of 298K 

• initial pressure of gaseous species is 1atm

• initial concentration of aqueous species is 1M EXCEPT for:

  • water (55.5M)

  • H⁺ (10^-7M)