Question

Name the products formed when:
(a) Carbon and concentrated nitric acid is heated
(b) Dilute $HN{O_3}$ is added to copper.

Answer 1

Nitric acid is a colourless and highly corrosive liquid with chemical formula $HN{O_3}$. It is a common laboratory reagent and is widely used in the chemical industry for the manufacture of fertilizers and explosives. It is toxic in nature and when exposed to skin can cause severe burns.

Complete answer:
Nitric acid is a strong acid i.e., it completely ionizes into its respective ions when dissolved in aqueous solution. The dissociation of nitric acid takes place as follows:
$HN{O_3} \rightleftharpoons {H_3}{O^ + } + NO_3^ -$
Nitric acid is a strong oxidizing agent because the nitrogen in $HN{O_3}$ exists in $+ 5$ oxidation state which is the maximum oxidation state in which nitrogen atoms can exist. So, the nitric acid has a tendency to undergo reduction to reduce the oxidation state of the nitrogen atom from $+ 5$ to $+ 3$. Thus, by reducing itself it acts as a strong oxidizing agent in a chemical reaction.
Now, let us check the given reactions involving nitric acid.
(a) Carbon and concentrated nitric acid is heated:
When carbon is heated with concentrated nitric acid, it gets oxidized to carbon dioxide along with the removal of nitrogen dioxide and water. The reaction takes place as follows:
$C + 4HN{O_3} \to C{O_2} + 2{H_2}O + 4N{O_2}$
(b) Dilute $HN{O_3}$ is added to copper.
When copper reacts with dilute nitric acid, it gets oxidized to copper nitrate along with the removal of nitric oxide and water. The reaction takes place as follows:
$3Cu + 8HN{O_3} \to 3Cu{(N{O_3})_2} + 4{H_2}O + 2NO$
Therefore, we can conclude that the major product formed in the reaction (a) and (b) is carbon dioxide and copper nitrate respectively.

Note:
It is important to note that the reaction of metals and non-metals with nitric acid depends on the temperature of the reaction and concentration of the acid. With dilute nitric acid, both metals as well as nonmetals tend to form nitric oxide whereas with concentrated nitric acid, formation of nitrogen dioxide is observed.