Question

What happens when sodium sulfite is treated with dilute hydrochloric acid?

Answer 1

Sodium sulfite, ${\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_3}$ is a salt formed from the reaction of sulfurous acid, ${{\text{H}}_2}{\text{S}}{{\text{O}}_3}$ and sodium hydroxide, ${\text{NaOH}}$. Dilute hydrochloric acid is a very strong acid. Dilute hydrochloric acid is prepared by adding water into the concentrated solution of hydrochloric acid.

Complete answer:
The chemical formula of sodium sulfite is ${\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_3}$ while the chemical formula of hydrochloric acid is ${\text{HCl}}$.
When sodium sulfite is reacted with dilute hydrochloric acid, the products formed are sulfur dioxide, sodium chloride and water molecules. The complete balanced chemical equation is given below:
${\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_3} + 2{\text{HCl}} \to 2{\text{NaCl}} + {\text{S}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}$
Sulfur dioxide molecule formed is a gas molecule. This gas smells like a burnt sulfur. We all know that the sulfur smells like rotten eggs. It is a colorless gas. Sulfur dioxide gas can be detected using a filter paper dipped in sodium chromate solution. This makes the color of filter paper change from orange to a green color. This is due to the conversion of chromium in $+ 6$ oxidation state to chromium in $+ 3$ oxidation state. Moreover, it is a toxic gas.

Note:
We may confuse sodium sulfate, sodium sulfite and sodium sulfide. Sodium sulfate is ${\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}$. Sodium sulfide is ${\text{N}}{{\text{a}}_2}{\text{S}}$. When sodium sulfate is reacted with hydrochloric acid, sulfuric acid and sodium chloride is formed. It is a reverse reaction.