Analytical Chemistry

Midterm 1

Standard State

free conditions in equilibrium, pure liquids and solids omitted

Enthalpy

∆H, heat absorbed/released, + is endothermic (heat absorbed), - is exothermic (heat liberated)

Entropy

∆S = ∆H/T, + is products are more disordered, - is products are less disordered

Free Energy (Gibbs)

energy is conserved, heat moves between system and surroundings, ∆G=∆H-T∆S, ∆G=∆Gº+RTlnQ

Q

reaction quotient used in chemical equilibrium

Q<K

reaction forms products until Q=K

Q>K

reaction forms reactants until Q=K

Ksp

solubility product constant, not including solids/liquids like K, when ion concentration exceeds Ksp, a solid precipitate will form and Ksp is satisfied

Common Ion Effect

a salt will be less soluble if ones of its constituents is already in solution

Complex Ion Effect

increased solubility arises from formation of complex ion, ions cause precipitation, form complex ions with complex mix of rxns, total concentration is dependent on each individual complex species

Activity

“apparent” concentration that accounts for ionic strength where concentrations are replaced with activities, activity coefficient often depends on ionic radius/ionic strength where it is a measure of deviation of behavior from the ideal (=1)

Ionic Strength

measure of the concentration of ions in solution

Regime 1: High Concentration

>10^-6M, amount added is equivalent to the [H+] and [OH-] from acids/bases, neglect autoprotolysis

Regime 2: Low Concentration

<10^-8M, only account for autoprotolysis, pH=7

Regime 3: Intermediate

10^-6 to 10^-8M, both added acid/base and autoprotolysis needs to be accounted for

Buffer

consists of a weak acid/base conjugate pair where concentrations are sufficient to dominate the pH of a solution and mitigate pH change with the addition of an acid or base

Principal Species

species that predominates in the solution at the given condition determined by comparing pH with pKa

Isoionic point

pH obtained when a pure and neutral polyprotic acid is dissolved in water

Isoelectric point

pH obtained when the average charge of a polyprotic acid is 0

Equivalence Point

titrant added is equal to the stoichiometric reaction analyte

Endpoint

color change of indicator to determine equivalence point

EDTA Titrations

determines metal chelate complexes, 7 different acid/base forms

Methods to determine titration end points

1. Metal ion indicator

2. Mercury electrode

3. pH electrode

4. Ion-sensitive electrode