AP Chemistry Unit 8: Acids and Bases

Vocabulary flashcards covering key terms, formulas, and concepts from AP Chemistry Unit 8 on Acids and Bases.

pH

The negative logarithm of the hydronium ion concentration, calculated as $-\log[H_3O^+]$.

pOH

The negative logarithm of the hydroxide ion concentration, calculated as $-\log[OH^-]$.

$$K_w$$

The product of the hydronium and hydroxide ion concentrations, which equals $1 \times 10^{-14}$ at $25\,^\circ C$.

Neutral Solution

Any solution where pH equals pOH; at $25\,^\circ C$, this corresponds to a pH and pOH of $7.00$.

Strong Acids

A group of six acids that ionize completely in solution, making the hydronium concentration equal to the concentration of the acid.

Strong Bases

Group 1 and 2 hydroxides that dissociate completely; when calculating pH for Group 2 hydroxides, there is a $2:1$ ratio of hydroxide to base concentration.

$$K_a$$

The equilibrium constant for the dissociation of a weak acid in a reversible reaction.

$$pK_a$$

The negative logarithm of the acid dissociation constant, represented as $-\log(K_a)$.

$$K_b$$

The equilibrium constant for a weak base reacting with water to form the conjugate acid and hydroxide ions.

$$pK_b$$

The negative logarithm of the base dissociation constant, represented as $-\log(K_b)$.

Percent Dissociation

The amount of acid that ionizes ($x$) divided by the initial acid concentration, multiplied by $100$.

Buffer

A mixture of a weak acid and its conjugate base that resists changes in pH when small amounts of acid or base are added.

Titration Curve

A plot of the pH of a mixture on the y-axis against the volume of titrant added on the x-axis.

Equivalence Point

The inflection point on a titration curve where the moles of base equal the moles of acid reacted.

Half Equivalence Point

The point in a titration where the pH equals the $pK_a$ of the weak acid and the concentrations of the weak acid and its conjugate base are equal.

Polyprotic Acids

Acids with multiple acidic hydrogens, identified by having multiple inflection points on a titration curve.

Bronsted-Lowry Base

A substance defined by its ability to attract protons, which are $H^+$ ions.

Organic Acid Strength

Determined by molecular structure; strength increases with the presence of more electronegative atoms like fluorine and a higher number of oxygen atoms.

Acid-Base Indicator

A substance used in titrations that changes color at a pH near its specific $pK_a$.

Henderson-Hasselbalch Equation

An equation used to calculate the pH of a buffer solution based on the $pK_a$ and the ratio of conjugate base to weak acid.

Buffer Capacity

The ability of a buffer to withstand a greater amount of acid or base without significant pH change, which increases with higher concentrations of the buffer components.

Le Chatelier's Principle (Solubility)

The principle explaining why lowering pH increases the solubility of compounds like magnesium carbonate by removing carbonate ions via reaction with added hydronium.