Question

What is the action of hot concentrated nitric acid on carbon?

Answer 1

Nitric acid is a strong oxidizing agent and it gives nascent oxygen both in concentrated as well as in diluted form as:
$2HN{O_3}(Conc.) \to {H_2}O + 2N{O_2} + [O]$
$2HN{O_3}(dil.) \to {H_2}O + 2NO + 3[O]$

Complete step by step answer:
Diluted nitric acid has no reaction on non-metal and since the carbon is non-metal there is no action of dilute nitric acid on it. But the concentrated nitric acid oxidizes non-metal such as carbon, sulphur, iodine, etc to their corresponding oxy-acids, and nitric acid itself is reduced to nitrogen dioxide.
The reaction of hot concentrated nitric acid with carbon is given as:
$[2HN{O_3} \to {H_2}O + 2N{O_2} + O] \times 2$
$\Rightarrow 4HN{O_3} \to 2{H_2}O + 4N{O_2} + 2O$ (1)
$C + 2[O] \to C{O_2}$ (2)
On adding equation (1) and (2) we get:
$C + 4HN{O_3} \to C{O_2} + 2{H_2}O + 4N{O_2}$
Hence we can say that the nitric acid oxidized carbon to carbon dioxide.

Additional information:
Nitric acid is a strong monobasic acid and in an aqueous solution it ionizes as:
$HN{O_3}(aq) + {H_2}O \to {H_3}{O^ + }(aq) + NO_3^ - (aq)$
Also, being a monobasic acid it reacts with metallic oxides, hydroxides, carbonates, and bicarbonates and gives salt known as nitrate. Aqua regia is formed using one part of concentrated $HN{O_3}$ and three parts of Concentrated $HCl$ and it is known to dissolve almost insoluble substances such as platinum and gold. It involves purification of gold and silver, manufacture of artificial silk, perfumes and in dyeing and printing

Note:
Nitric acid is highly corrosive in nature and is a toxic, colorless, and fuming liquid. It finds its application as an important industrial chemical in the manufacture of explosives and fertilizers. It performs a neutralization reaction with ammonia to form ammonium nitrate which is used in fertilizers and the common explosive TNT also contains nitric acid.