Question

Why does sulphur dioxide gas evolved when $HCl$ gas is added?

Answer 1

Hint: We know that the sulfur dioxide and hydrogen chloride is caused by the combustion reaction. The sulfur dioxide is a chemical compound having the formula, \[S{O_2}\]. This gas is behind the smell of burnt matches and it’s a toxic gas. And hydrogen chloride is a chemical compound with formula, $HCl$. When sulfur is reacting with hydrogen chloride at room temperature, there is a formation of sulfur chloride with hydrogen gas.

Complete answer:
 When sodium thiosulphate is reacting with hydrogen chloride, there is a formation of sodium chloride, water, sulphur and sulphur dioxide. The reaction can be written as,
\[N{a_2}{S_2}{O_3} + 2HCl \to 2NaCl + {H_2}O + S{O_2} + S\]
Here, the sulphur dioxide gas is evolved during the reaction. The sulphur dioxide gas is evolved when hydrogen chloride gas is added. Because, the sulphur is a non – metal and it will not react with acids. And the sulphur is less reactive compared to hydrogen. Therefore, from hydrochloric acid, the hydrogen is not displaced by the sulphur atom. And there will not undergo any reaction between hydrochloric acid and sulphur atoms. The formation of sulphur dioxide and hydrochloric acid takes place by combustion reaction.

Note:
We need to know that when sodium sulphite is reacting with dilute hydrochloric acid, the sulphur dioxide gas will evolve during the reaction and there is a smell of burning sulphur. Sulphur is an element having yellow colour and it is a crystalline solid. But the sulphur dioxide is a colorless gas having a pungent smell. And it is soluble in water very easily. But the hydrogen is a gas and it is more reactive than sulphur.