Study of Compounds — Nitric Acid — Question 19

(i) Saw dust bursts into flames when hot conc. nitric acid is poured on it. The reason is that Nitric acid is a strong oxidising agent. It decomposes to give nascent oxygen which oxidises organic compounds to carbon dioxide and water.

Saw dust [C₆H₁₀O₅]_n + Nitric acid [hot conc.] ⟶ carbon dioxide + water + nitrogen dioxide.

(ii) (a) When conc. nitric acid is heated in absence of copper, reddish brown fumes of nitrogen dioxide are evolved.

$4\text{HNO}_3 \xrightarrow{\Delta} \text{4NO}_2 + \text{2H}_\text{2}\text{O} + \text{O}_2$

(ii) (b) Cu reacts with conc. nitric acid liberating reddish brown fumes of nitrogen dioxide along with blue coloured solution of copper nitrate.

Cu + 4HNO₃ [conc.] ⟶ Cu(NO₃)₂ + 2H₂O + 2NO₂