Weak acid

A weak acid is an acid chemical which does not dissociate (split into ions) completely in water solution. This means it does not give all its hydrogen ions into the water. Weak acids typically have a pH between 3 and 6.

Acids and bases
Acceptor number Acid Acid–base reaction Acid–base homeostasis Acid strength Acidity function Amphoterism Base Buffer solutions Dissociation constant Donor number Equilibrium chemistry Extraction Hammett acidity function pH Proton affinity Self-ionization of water Titration Lewis acid catalysis Frustrated Lewis pair Chiral Lewis acid
Acid types
Brønsted–Lowry Lewis Mineral Organic Oxide Strong Superacids Weak Solid
Base types
Brønsted–Lowry Lewis Organic Oxide Strong Superbases Non-nucleophilic Weak

Acetic acid (CH₃COOH) and oxalic acid (H₂C₂O₄) are examples of weak acids. If an acid is represented by HA, then there is a balance between molecules which are split (ionised), and molecules which are not:

${\displaystyle \mathrm {HA_{(aq)}\,\leftrightarrow \,H^{+}\,_{(aq)}+\,A^{-}\,_{(aq)}} }$

The relative strength of an acid can be expressed using K_a, the acid ionization constant. In general, the larger a K_a, the stronger the acid, while a smaller K_a indicates a relatively weaker acid. Weak acids will have a K_a value of less than 1, while strong acids will have a K_a value greater than 1.