Question

In the laboratory preparation of nitric acid the mixture of con. H₂SO₄ and sodium nitrate should not be heated very strongly above 200°C. Give scientific reasons :

Answer 1

The mixture of sodium nitrate and conc. H₂SO₄ should not be heated very strongly above 200°C because

it has following disadvantages. 

(1)  Sodium sulphate is formed at high temperature. Which is hard substance like some and it is very difficult to remove from the distilating flask.

(2)  Glass apparatus may crack above 200°C 

(3)  A part of citric acid vapors decompose to give NO₂ which imparts a yellow color to nitric acid.