Calculations Involving Ka and Kb

Vocabulary terms and fundamental formulas for acid-base equilibrium calculations from the PreAP Chemistry lecture notes.

pH Formula

$$pH = - \log[H_3O^+]$$

[H3O+] Calculation

$$[H_3O^+] = 10^{-pH}$$

pOH Formula

$$pOH = -\log[OH^-]$$

[OH–] Calculation

$$[OH^-] = 10^{-pOH}$$

pH and pOH Relationship

$$pH + pOH = 14$$

Kw (Ion-Product Constant for Water)

$$K_w = [H_3O^+][OH^-] = 1 \times 10^{-14}$$

Acid Dissociation Equation (General)

$$HA + H_2O \rightleftharpoons A^- + H_3O^+$$

Base Dissociation Equation (General)

$$B + H_2O \rightleftharpoons BH^+ + OH^-$$

Strong Acid/Base Dissociation

A process where the substance completely dissociates in water, meaning $[\text{initial acid/base concentration}] = [\text{final ion concentration}]$.

Acetic Acid

A weak acid with the formula $HC_2H_3O_2$ (or $CH_3COOH$) and a $K_a$ of $1.8 \times 10^{-5}$.

Lactic Acid

$HC_3H_5O_3$; a waste product that accumulates in muscle tissue during exertion, leading to pain and fatigue.

Negligible Change Assumption

The assumption that the amount a concentration changes ($x$) is so small relative to the initial concentration that it can be ignored, typically applied when $K_a$ is very small (e.g., $10^{-5}$).

Relationship between Ka and Kb

$$K_w = K_a \times K_b = 1 \times 10^{-14}$$

Ka (Lactic Acid)

$$1.4 \times 10^{-4}$$

Conjugate Base of Lactic Acid

$$C_3H_5O_3^-$$