Question

State why the basicity of acitic acid is one and calcium hydroxide is two?

Answer 1

• Basicity of an acid is the number of hydrogen ions which can be produced from one molecule of the acids on complete dissociation.
  

$C{H}_{3}COOH\rightleftharpoons {C{H}_{3}COO}^{-}+H^{+}$

Acetic acid $\left(C{H}_{3}COOH\right)$ gives one $H^{+}$ per molecule of the acid, hence acetic acid is monobasic, i.e., its basicity is one.

• Acidity of a base is the number of hydroxyl ions which can be produced from one molecule of the base on complete dissociation.
  

$Ca{\left(OH\right)}_2\rightleftharpoons {Ca}^{+2}+2{OH}^{-}$

Calcium hydroxide $Ca{\left(OH\right)}_2$ gives two hydroxyl ions per molecule of the base, hence calcium hydroxide is di-acidic, i.e., its acidity is two.