Give reasons for the following.

(a) Sulphuric acid forms two types of salts with NaOH.

(b) A piece of wood becomes black when concentrated sulphuric acid is poured on it.

(c) Brisk effervescence is seen when oil of vitriol is added to sodium carbonate.

(a) Sulphuric acid forms two types of salts i.e., acid salt and normal salt with an NaOH (alkali) since it's basicity is two.

NaOH [insufficient] + H₂SO₄ ⟶ H₂O + NaHSO₄ [acid salt]

2NaOH [excess] + H₂SO₄ ⟶ 2H₂O + Na₂SO₄ [normal salt]

(b) A piece of wood becomes black because of the dehydrating property of sulphuric acid. It readily removes elements of water from other compounds.

$[\text{C}${6}\text{H}{10}\text{O}{5}]\text{n}\xrightarrow{\text{Conc. H}2\text{SO}4} \text{6[C]}\text{n} + \text{5[H}2\text{O}]\text{n}

(c) When oil vitriol is added to sodium carbonate brisk effervescence are seen due to the evolution of Carbon dioxide.

Na₂CO₃ + H₂SO₄ ⟶ H₂O + Na₂SO₄ + CO₂ ↑