Solutions, Acids & Bases, and Redox Reactions & Electrochemistry

MCAT Prep: General Chemistry Part 6

water soluble

All salts containing alkali metal (Group 1) or ammonium (NH₄⁺) cations and nitrate (NO₃^-) or acetate (CH₃COO^-) anions are __________

Ag+, Pb2+, Hg2+

All chlorides, bromides, and iodides are water soluble, with the exception of ___________

Ca2+, Sr2+, Ba2+, Pb2+

All salts of the sulfate ion (SO₄^2-) are water soluble, with the exception of ______________

insoluble

All metal oxides are ___________, with the exception of the alkali metals and CaO, SrO, BaO, al of which hydrolyze to form solutions of the corresponding metal hydroxides

hydroxides

All ________ are insoluble, with the exception of the alkali metals and Ca²⁺, Sr²⁺, and Ba²⁺

insoluble

All carbonates (CO₃^2-), phosphates (PO₄^3-), sulfides (S^2-), and sulfites (SO₃^2-) are ____________, with the exception of the alkali metals and ammonium

Percent composition by mass

(Mass of solute / mass of solution) x 100%

Mole fraction

# of mol of compound / total # of moles in system

Molarity

# of mol of solute / liter of solution

Molality

# of mol of solute / kg of solvent

Normality

# of gram equivalent weights of solute / liter of solution

Arrhenius definition

an acid is a species that produces excess H+ (protons) in an aqueous solution, and a base is a species that produces excess OH^- (hydroxide ions)

Bronsted-Lowry definition

an acid is a species that donates protons, while a base is a species that accepts protons

Lewis definition

an acid is an electron pair acceptor, and a base is an electron pair donor

properties of acids and bases

pH = -log[H⁺] = log (1/[H⁺])

pOH = -log[OH^-] = log (1/[OH^-])

H₂O (l) ⇌ H⁺ (aq) + OH^- (aq)

K_w = [H⁺][OH^-] = 10^-14

pH + pOH = 14

weak acids and bases

HA (aq) + H₂O (l) ⇌ H₃O⁺ (aq) + A^- (aq)

K_a = ([H₃O⁺][A^-])/([HA])

K_b = ([B⁺][OH^-])/([BOH])

Strong acids

HCl, HI, HBr, H₂SO₄, HClO₃, HClO₄, HNO₃

strong bases

LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)₂, Sr(OH)₂, Ba(OH)₂

Amphoteric species

is one that can act either as an acid or a base, depending on its chemical environment

Titration

a procedure used to determine the molarity of an acid or base by reacting a known volume of a solution of unknown concentration with a known volume of a solution of known concentration. The half-equivalence point defines pH = pK_a

Henderson-Hasselbalch equation

is used to estimate the pH of a solution in the buffer region where the concentrations of the species and its conjugate are present in approximately equal concentrations

pH = pK_a + log ([conjugate base]/[weak acid])

pOH = pK_b + log ([conjugate acid]/[weak base])

Oxidation

loss of electrons

Reduction

gain of electrons

Oxidizing agent

causes another atom to undergo oxidation, and is itself reduced

Reducing agent

causes another atom to be reduced, and is itself oxidized

Galvanic

________ cell reactions supply energy and are used to do work

Half-cells

separate containers where the energy of galvanic cell reactions can be harnessed by placing the oxidation-reduction half-reactions into this. These are then connected by an apparatus that allows for the flow of electrons

electrolytic cell

A redox reaction occurring in an ___________ has a positive ΔG and is therefore nonspontaneous

electrical energy

In electrolysis, ___________ is required to induce a reaction

Reduction potential

of each species is defined as the tendency of a species to acquire electrons and be reduced. Standard of this, E°, is measured under standard conditions: 25°C, 1 M concentration for each ion in the reaction, a partial pressure of 1 atm for each gas and metals in their pure state

Standard reduction potentials

are used to calculate the standard electromotive force (emf or E°_cell) of a reaction, the difference in potential between two half-cells

emf = E°_{red, cathode} - E°_{red, anode}

Gibbs free energy

ΔG; is the thermodynamic criterion for determining the spontaneity of a reaction

ΔG = -nFE_cell