Question

68. Define basicity of an acid and acidity of a base. On the basis of these, explain the classification of acids and bases. Give suitable examples.

Answer 1

Part 1: Basicity of acid and their classification

Basicity of acid: Basicity of the base is defined as the number of hydrogen ions (H⁺) furnished by per molecule of the acid in its aqueous solution.

Types of acids:

• Monobasic acids are those acids that produce only one hydrogen ion per molecule of the acid in their aqueous solution.
• Example: Hydrochloric acid (HCl)

$\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Hydrogen}\mathrm{ion}}{{\mathrm{H}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Chloride}\mathrm{ion}}{{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)}$

• Dibasic acids are those acids that produce two hydrogen ions per molecule of the acid in their aqueous solution.
• Example: Sulphuric acid (H₂SO₄)

$\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Hydrogen}\mathrm{ion}}{2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Sulphate}\mathrm{ion}}{{\mathrm{SO}}_4^{2-}\left(\mathrm{aq}\right)}$

• Tribasic acids are those acids that produce three hydrogen ions per molecule of the acid in their aqueous solution.
• Example: Phosphoric acid (H₃PO₄)

$\underset{\mathrm{Phosphoric}\mathrm{acid}}{{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)}\rightleftharpoons \underset{\mathrm{Hydrogen}\mathrm{ion}}{3{\mathrm{H}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Phosphate}\mathrm{ion}}{{\mathrm{PO}}_4^{3-}\left(\mathrm{aq}\right)}$

.Part 2: Acidity of base and their classification

Acidity of base: Acidity of the base is defined as the number of hydroxide (OH^-) ions furnished by per molecule of the base in its aqueous solution.

Types of bases:

• Monoacidic bases are those bases that produce only one hydroxide ion per molecule of the base in their aqueous solution.
• Example: Sodium hydroxide (NaOH)

$\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{ion}}{{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}$

• Diacidic bases are those bases that produce two hydroxide ions per molecule of the base in their aqueous solution.
• Example: Calcium hydroxide [Ca(OH)₂]

$\underset{\mathrm{Calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}\to \underset{\mathrm{Calcium}\mathrm{ion}}{{\mathrm{Ca}}^{2+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{2{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}$

• Triacidic bases are those bases that produce three hydroxide ions per molecule of the base in their aqueous solution.
• Example: Aluminum hydroxide [Al(OH)₃]

$\underset{\mathrm{Aluminum}\mathrm{hydroxide}}{\mathrm{Al}{\left(\mathrm{OH}\right)}_3\left(\mathrm{aq}\right)}\rightleftharpoons \underset{\mathrm{Aluminum}\mathrm{ion}}{{\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{3{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}$