Question

In the preparation of nitric acid fromKNO₃ and NaNO₃ ,why other concentrated acids are not used in place off concentrated sulphuric acid?

Answer 1

Only acids stronger than nitric acids can be used in the preparation because only those will produce the nitric acid in the undissociated form. As sulphuric acid is an stronger acid than nitric acid, it is used. Other stronger acids like the halogen acids (e.g. HCl, HI) are not used because there concentrated solutions have low boiling points.

NaNO₃ + H₂SO₄ $\stackrel{573K}{\to }$ NaHSO₄ + HNO<sub>3

During the preparation, the reactants are mixed and heated to about 200^oC. As the halogen acids will be gases at this temperature, the mixing will not take place and it will require high pressures. Therefore, the reaction conditions will have to altered and would be difficult to control.</sub>