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°C. 

Answer 1

The temperature of the mixture of concentrated sulphuric acid and sodium nitrate should not exceed 200oC 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.
`NaNO_3 + NaHSO_4` `Na_2SO_4 + HNO_3`