Question

Identify the anion present in the following compounds:

A salt D on treatment with Dilute Sulphuric acid produces a gas which turns lime water milky but no effect on acidified potassium chromate solution.

Answer 1

Explanation:

• When dilute Sulphuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$ is added to a metallic carbonate, a colorless and odorless Carbon dioxide $\left(C{O}_2\right)$ gas is evolved with brisk effervescence.
• Here the metallic carbonate will be Sodium carbonate$\left(N{a}_{2}C{O}_3\right)$.
• The chemical reaction is as follows.

$\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)}\to \underset{\mathrm{Sodium}\mathrm{sulphate}}{{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

• Carbon dioxide gas which is going to be produced in the above chemical reaction turns lime water milky and has no effect on acidified potassium dichromate $\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$ solution.
• The chemical reaction is as follows.

$\underset{\mathrm{Calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}+\underset{\mathrm{carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}(\mathrm{white}\mathrm{ppt})+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

• Therefore, the anion present is carbonate $\left({{\mathrm{CO}}_3}^{2-}\right)$ as it is detected by dilute Sulphuric acid.