Question

Describe the reactions that show
(i) Concentrated sulphuric acid is a non-volatile acid.
(ii) Concentrated sulphuric acid acts as a dehydrating agent.
(iii) Concentrated sulphuric acid is an oxidising agent.
(iv) Dilute sulphuric acid behaves as dibasic acid.

Answer 1

(i) Non-volatile nature: The non-volatile nature of concentrated sulphuric acid is demonstrated by its reaction with salts of volatile acids such as chlorides or nitrates.

MCl + H₂SO₄ → MHSO₄ + HCl
MNO₃ + H₂SO₄ → MHSO₄ + HNO₃

(ii) Dehydrating agent: Concentrated sulphuric acid removes water molecules from hydrated salts and carbohydrates.

Hydrated salt $\stackrel{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }$ Anhydrous salt + (H₂O)_n
(C₆H₁₀O₅)_n $\stackrel{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }$ 5(C)_n + 6(H₂O)_n

(iii) Oxidising agent: Concentrated sulphuric acid oxidises non-metals to their corresponding salts.

A + H₂SO₄ → AO + H₂O + SO₂

(iv) Dibasic acid: dilute sulphuric acid ionises in two steps, demonstrating its dibasic nature.

H₂SO₄ + H₂O ⇌ HSO₄^- + H₃O⁺
HSO_4^- + H₂O ⇌ SO_4^2- + H₃O⁺