Give preparation of Nitric acid.

Explanation

Laboratory preparation : In laboratory, nitric acid is prepared by heating `KNO_3` or `NaNO_(3)` and concentrated `H_2SO_(4)` in a glass retort.
`NaNO_(3) + H_(2)SO_(4) to NaHSO_(4) + HNO_(3)`
Industrial preparation (Ostwald.s process) : This method is based upon the catalytic oxidation of `NH_3` by atmospheric oxygen.
`4NH_(3)(g) + underset("From air") (5O_(2)(g)) overset("Pt//Rh gauge catalyst") underset("500 K, 9 bar") to 4NO_(g) + 6H_(2)O(g)`
Nitric oxide thus formed combines with oxygen giving `NO_(2)`
`2NO(g) + O_(2)(g) Nitrogen dioxide so formed, dissolves in water to give `HNO_(3)`
`3NO_(2)(g) + H_(2)O(l) to 2HNO_(3)(aq) + NO(g)`
NO thus formed is recycled and the aqueous HN03 can be concentrated by distillation upto 68% by mass. Further concentration to 98% can be achieved by dehydration with cone. `H_2SO_(4)`.