Question

(a) Nitric acid cannot be concentrated beyond 68% by the distillation of a dilute solution of HNO₃. State the reason.
(b) How can 68% nitric acid be concentrated to 98% nitric acid?

Answer 1

(a) At 68% concentration, nitric acid forms an azetropic mixture that boils at a constant temperature with water. This mixture boils at 121^oC.
(b) 68% nitric acid can be concentrated to 98% nitric acid by distillation with concentrated sulphuric acid under reduced pressure.