Question

Give reasons for the following:
In the laboratory preparation of nitric acid, the mixture of concentrated sulphuric acid and sodium nitrate should not be heated very strongly above ${200}^{\circ }C$.

Answer 1

The temperature of the mixture of concentrated sulphuric acid and sodium nitrate should not exceed ${200}^{\circ }$ because sodium sulphate formed at higher temperature forms a hard crust which sticks to the walls of the retort and is difficult to remove. At higher temperature nitric acid may also decompose.

$NaN{O}_3+NaHS{O}_4\stackrel{>{200}^{\circ }}{⟶}N{a}_{2}S{O}_4+HN{O}_3$