The figure given below illustrates the apparatus used in the laboratory preparation of nitric acid.

(a) Name A (a liquid), B (a solid) and C (a liquid). (Do not give the formulae).

(b) Write a balanced chemical equation for the above preparation.

(c) Why is an all glass apparatus used ?

(d) The acid prepared is yellow in colour. Why?

(e) How is this colour removed?

(a)

A — Concentrated sulphuric acid,

B — Sodium nitrate or potassium nitrate

C — Nitric acid.

(b)

$\underset{[\text{conc.}]}{\text{KNO}$3} + \underset{[\text{conc.}]}{\text{H}2\text{SO}4} \xrightarrow{\lt 200 \degree\text{C}} \underset{[\text{acid salt}]}{\text{KHSO}4} + \text{HNO}_3

(c) All glass apparatus is used in the laboratory preparation of nitric acid since the vapours of nitric acid being highly corrosive attack rubber, cork, etc.

(d) Pure nitric acid [HNO₃] is colourless and unstable and decomposes slightly even at ordinary temperatures and in the presence of sunlight. The decomposition results in formation of reddish brown nitrogen dioxide [NO₂] which remains dissolved in the acid thus imparting a slight yellowish brown colour.

(e) If dry air or CO₂ is bubbled through the yellow acid, the latter turns colourless because it drives out NO₂ from warm acid which is further oxidised to nitric acid.