Question

Identify the gas evolved and give the chemical test in each of the following cases:
A.Dilute hydrochloric acid reacts with sodium sulphite
B.Dilute hydrochloric acid reacts with iron (II) sulphide.

Answer 1

When dilute hydrochloric acid reacts with sodium sulphite, sulphur-di-oxide gas is evolved along with Sodium chloride and water and when dilute hydrochloric acid reacts with iron (II) sulphide, Hydrogen sulphide $({H_2}S)$ gas is evolved along with ferrous chloride.

Complete step by step answer:
A.Dilute hydrochloric acid reacts with sodium sulphite
So, we can write the following equation for it:
$2HCI + N{a_2}S{O_3} \to 2NaCI + {H_2}O + S{O_2}$
In this case, sulphur-di-oxide gas (SO2) is evolved in the above reaction with the formation of sodium chloride. It is a colourless gas having the suffocating smell of burning sulphur. It changes freshly prepared acidified potassium dichromate (Kr2Cr2O7) from orange to green.
B.Dilute hydrochloric acid reacts with iron (II) sulphide.
So, we can write the following equation for it:
$HCI + Fes \to {H_2}S + FeC{I_2}$
In this case, hydrogen sulphide $({H_2}S)$ gas is evolved in the above reaction along with the formation of ferrous chloride $(FeC{I_2})$ . It is a colourless gas with a smell of rotten eggs. It changes lead nitrate solution paper black.

Note: Sulphur-di-oxide gas is a colourless gas having the suffocating smell of burning sulphur. It irritates the risk of tract infection and causes coughing, mucus secretion and the conditions such as asthma and chronic bronchitis are aggravated. Hydrogen sulphide gas is a colourless gas with a smell of rotten eggs and it can irritate eyes, throat and nose. It is highly flammable explosive gas. It also burns and produces other toxic vapours, also it is heavier than air, so it may settle at low spots.