Question

State one chemical test between the following pair:

Sodium carbonate and Sodium sulphite.

Answer 1

Dilute Hydrochloric acid test (HCl):

• Add dilute Hydrochloric acid $\mathbf{\left(}\mathbf{HCl}\mathbf{\right)}$ to both the compounds i.e., Sodium carbonate $\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$ and Sodium sulphite $\left({\mathrm{Na}}_2{\mathrm{SO}}_3\right)$ and pass the liberated gas through acidified Potassium dichromate solution $\left(K_2{\mathrm{Cr}}_2{O}_7\right)$.
• When dilute $\mathrm{HCl}$ is added to the Sodium Carbonate $\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$, it will liberate ${\mathrm{CO}}_2$ gas.
• When ${\mathrm{CO}}_2$ gas passed through the acidified Potassium dichromate solution $\left(K_2{\mathrm{Cr}}_2{O}_7\right)$, it does not show any change in the color of the solution.

Balanced chemical equation:

$\underset{\mathrm{Sodium}\mathrm{carbonate}}{\underbrace{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)}}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\underbrace{2\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{\mathrm{Sodium}\mathrm{chloride}}{\underbrace{2\mathrm{NaCl}\left(\mathrm{aq}\right)}}+\underset{\mathrm{water}}{\underbrace{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}+\underset{\mathrm{carbon}\mathrm{dioxide}\mathrm{gas}}{\underbrace{{\mathrm{CO}}_2\left(\mathrm{g}\right)}}$

• While when dilute $\mathrm{HCl}$ is added to the Sodium Sulphite $\left({\mathrm{Na}}_2{\mathrm{SO}}_3\right)$, it will liberate ${\mathrm{SO}}_2$ gas.
• When ${\mathrm{SO}}_2$ gas passed through the acidified Potassium dichromate solution $\left(K_2{\mathrm{Cr}}_2{O}_7\right)$, it will turn the potassium dichromate solution green.

Balanced chemical equation:

$\underset{\mathrm{Sodium}\mathrm{sulphite}}{\underbrace{{\mathrm{Na}}_2{\mathrm{SO}}_3\left(\mathrm{s}\right)}}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\underbrace{2\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{\mathrm{Sodium}\mathrm{chloride}}{\underbrace{2\mathrm{NaCl}\left(\mathrm{aq}\right)}}+\underset{\mathrm{water}}{\underbrace{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}+\underset{\mathrm{Sulphur}\mathrm{dioxide}\mathrm{gas}}{\underbrace{{\mathrm{SO}}_2\left(\mathrm{g}\right)}}$