Why is:

(a) Concentrated sulphuric acid kept in air-tight bottles?

(b) H₂SO₄ is not used as a drying agent for H₂S?

(c) Sulphuric acid used in the preparation of HCl and HNO₃? Give equations in both cases.

(a) As concentrated sulphuric acid is hygroscopic and has a great affinity for water hence, it absorbs moisture from the atmosphere. Therefore, it is kept in air tight bottles.

(b) Sulphuric acid is not a drying agent for H₂S because it reacts with H₂S to form sulphur.
H₂S + H₂SO₄ ⟶ S + 2H₂O + SO₂ ↑

(c) Concentrated sulphuric acid has a high boiling point (338°C) and so it is considered to be a non-volatile acid. It is, therefore, used for preparing volatile acids like hydrochloric acid and nitric acid from their salts by double decomposition.

NaCl + H₂SO₄ [conc.] $\xrightarrow{\lt 200 \degree\text{C}}$ NaHSO₄ + HCl

NaNO₃ + H₂SO₄ [conc.] $\xrightarrow{\lt 200 \degree\text{C}}$ NaHSO₄ + HNO₃