Common Strong & Weak Acids/Bases Cheat Sheet

Key Facts

• The common strong acids are $\mathrm{HCl}$, $\mathrm{HBr}$, $\mathrm{HI}$, $\mathrm{HNO_3}$, $\mathrm{HClO_4}$, $\mathrm{HClO_3}$, and $\mathrm{H_2SO_4}$ for its first ionization.
• A strong acid dissociates essentially completely in water, such as $\mathrm{HCl(aq) \rightarrow H^+(aq) + Cl^-(aq)}$.
• Common weak acids include $\mathrm{HF}$, $\mathrm{CH_3COOH}$, $\mathrm{H_2CO_3}$, $\mathrm{H_3PO_4}$, $\mathrm{HCN}$, and $\mathrm{H_2S}$.
• A weak acid partially ionizes in water, such as $\mathrm{CH_3COOH(aq) \rightleftharpoons H^+(aq) + CH_3COO^-(aq)}$.
• Strong bases include Group $1$ hydroxides such as $\mathrm{NaOH}$ and $\mathrm{KOH}$, plus soluble Group $2$ hydroxides such as $\mathrm{Ca(OH)_2}$, $\mathrm{Sr(OH)_2}$, and $\mathrm{Ba(OH)_2}$.
• A strong base dissociates completely to produce hydroxide ions, such as $\mathrm{Ba(OH)_2(aq) \rightarrow Ba^{2+}(aq) + 2OH^-(aq)}$.
• Common weak bases include $\mathrm{NH_3}$, amines such as $\mathrm{CH_3NH_2}$, and many anions that accept $\mathrm{H^+}$ from water.
• For a weak acid $\mathrm{HA}$, $K_a = \frac{[\mathrm{H^+}][\mathrm{A^-}]}{[\mathrm{HA}]}$, and for a weak base $\mathrm{B}$, $K_b = \frac{[\mathrm{BH^+}][\mathrm{OH^-}]}{[\mathrm{B}]}$.

Vocabulary

Strong acid

A strong acid is an acid that essentially completely ionizes in water to produce $\mathrm{H^+}$ or $\mathrm{H_3O^+}$.

Weak acid

A weak acid is an acid that only partially ionizes in water and forms an equilibrium mixture of acid and ions.

Strong base

A strong base is a base that dissociates completely in water to produce $\mathrm{OH^-}$ ions.

Weak base

A weak base is a base that partially reacts with water to form $\mathrm{OH^-}$ and its conjugate acid.

Conjugate acid-base pair

A conjugate acid-base pair consists of two species that differ by exactly one proton, $\mathrm{H^+}$.

Ionization constant

An ionization constant such as $K_a$ or $K_b$ measures how strongly an acid or base forms ions at equilibrium.