Chemistry Exam 3: Acids, Bases, and Buffers Review

A comprehensive set of flashcards covering key concepts, definitions, and equations related to acids, bases, and buffers in a chemistry context.

Buffer

A solution that resists changes in pH when small amounts of acid or base are added.

Good buffer components

A weak acid and its conjugate base or a weak base and its conjugate acid.

Effectiveness of a buffer

A buffer is most effective when pH is approximately equal to pKa (within ±1).

High capacity buffer

A buffer has the highest capacity when it has high concentrations and a ~50/50 ratio of acid to base.

Mixtures that form buffers

A mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

Mixtures that do NOT form buffers

A strong acid and a strong base.

Henderson–Hasselbalch Equation

The equation used to calculate pH: $pH=pKa+\log_{}\left(\frac{base}{acid}\right).$ Used to calculate the pH of a buffer

Relationship between Ka and pKa

pKa = -log(Ka).

Expression for Ka

The expression for acid dissociation constant Ka is Ka = rac{[H^+][A^-]}{[HA]}.

Expression for Ksp

The expression for solubility product constant Ksp for the reaction $AB <br /> ightleftharpoons A^+ + B^-$ is $Ksp = [A^+][B^-]$.

Ksp in terms of solubility (S)

For the compound SrF₂, $Ksp = [Sr^{2+}][F^-]^2 = S(2S)^2 = 4S^3$.

General rule for Ksp with coefficients

Raise each ion concentration in the Ksp expression to the power of its coefficient.

pH at equivalence (strong acid + strong base)

The pH is equal to 7.

pH at equivalence (weak acid + strong base)

The pH is greater than 7.

pH at equivalence (weak base + strong acid)

The pH is less than 7.

Half-equivalence point

At the half-equivalence point, pH equals pKa.

Species at equivalence for weak acid titration

The species that dominates is the conjugate base.

Species at equivalence for weak base titration

The species that dominates is the conjugate acid.

Molar solubility (S)

The amount of solute that dissolves per liter (mol/L).

Ksp relation to solubility

A larger Ksp value indicates a more soluble compound.

Ksp expression for Cu(OH)₂

For $Cu(OH)₂ <br /> ightarrow Cu^{2+} + 2OH^-$, Ksp is calculated as $Ksp = [Cu^{2+}][OH^-]^2 = S(2S)^2 = 4S^3$.

Effect of adding HCl to a buffer

When HCl is added to a buffer, A⁻ decreases and HA increases.

Effect of adding NaOH to a buffer

When NaOH is added to a buffer, HA decreases and A⁻ increases.

First step in buffer problems with added acid/base

The first step is to perform stoichiometry BEFORE using the Henderson–Hasselbalch equation.

Finding pKa from a titration curve

The pKa can be found at the half-equivalence point of the titration curve.

Identifying acid vs base from titration curve

If the curve starts at low pH, it indicates an acid; a high pH indicates a base.

Monoprotic vs diprotic identification

The number of equivalence points on the titration curve indicates if the acid or base is monoprotic or diprotic.

Equilibrium states

Equilibrium is dynamic, not static.

Catalysts consumption

Catalysts are not consumed in a reaction.

Effect of catalysts on equilibrium constant

Catalysts do not change the equilibrium constant.

Effect of reversing a reaction on K

Reversing a reaction changes K such that new K = 1/old K.

Effect of doubling a reaction on K

Doubling a reaction changes K to K squared.

Best buffer pH range

The optimal pH range for a buffer is pKa ± 1.

Stronger acid and Ka relationship

A stronger acid has a larger Ka.

Stronger acid and pKa relationship

A stronger acid has a smaller pKa.