Question

Iron reacts with conc. $HCl$ and conc. ${H_2}S{O_4}$ . But it does not react with conc. $HN{O_3}$ . Suggest your answer with the proper reason.

Answer 1

We need to know that the iron is one of the transition metals in the periodic table. In our daily life, iron plays an important role in major things. The atomic symbol of iron is $Fe$ . We must remember that the atomic number of iron is $26$ . General metals are highly reactive in inorganic acid.

Complete step by step answer:
We must have to know that the iron reacts with inorganic acid to form respect for ferric salt.
Iron reacts with conc. $HCl$ to form iron chloride (ferric chloride and ferrous chloride) .
$Fe + 2HCl \to FeC{l_2} + {H_2}$
$2Fe + 6HCl \to 2FeC{l_3} + 3{H_2}$
Iron reacts with conc. ${H_2}S{O_4}$ to form iron sulphate (ferric sulphate and ferrous sulphate).
$Fe + {H_2}S{O_4} \to FeS{O_4} + {H_2}$
So, iron reacts with conc. $HCl$ and conc. ${H_2}S{O_4}$ .
We expect this kind of reaction to occur when iron reacts with conc. $HN{O_3}$ and to form iron nitrate. But not able to form nitrate here.
But, iron doesn’t react with conc. $HN{O_3}$. Because, conc. $HN{O_3}$ is a strong oxidising agent. It reacts with iron immediately to form an iron oxide layer. This layer is like a coating to prevent further reactivity of iron. This iron oxide surface renders iron passive in reactivity. This kind action is known as passivity.
$Fe + 2HN{O_3} \to FeO + 2N{O_2} + {H_2}O$
From the above discussion, we will conclude iron metal reacts with conc. $HCl$ and conc. ${H_2}S{O_4}$, but not react with conc. $HN{O_3}$ due to formation of iron oxide.

Note: We must know that iron metal has two oxidation states. There are $F{e^{ + 2}}$ and $F{e^{ + 3}}$ . $F{e^{ + 2}}$ is called ferrous salt. $F{e^{ + 3}}$ is known as ferric salt. Nitric acid is the strong oxidising agent for all the metals. $F{e^{ + 3}}$ is a more stable iron cation than $F{e^{ + 2}}$ . $F{e^{ + 3}}$ having half-filled $d$ orbitals. $F{e^{ + 2}}$ having partially filled $d$ orbitals. In general, half-filled orbitals are more stable than partially filled orbitals.