Question

(i) Dilute nitric acid is generally considered to be a typical acid except for its reaction with metals. In what way is dilute nitric acid different from other acids when it reacts with metals?
(ii) Write the equation for the reaction of dilute nitric acid with copper.
(iii) Account for the yellow colour that appears in concentrated nitric acid when it is left standing in an ordinary glass bottle.

Answer 1

1. Dilute nitric acid reacts with metals to produce nitric oxide and metal nitrate. This is in contrast to other dilute acids that react with metals to produce hydrogen gas.
2. $3\mathrm{Cu}+8{\mathrm{HNO}}_3\to 3\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+4{\mathrm{H}}_2\mathrm{O}+2\mathrm{NO}$
3. When concentrated nitric acid is left in a glass container, nitrogen dioxide formed by the oxidation of nitric acid dissolves in the acid and imparts it a yellowish brown colour.