Question

Which of the following reagents is used to test the presence of ${\mathrm{SO}}_2$ Gas?

• A. Alkaline Potassium Manganate
• B. Alkaline Potassium Dichromate
• C. Acidified Potassium Manganate
• D. Acidified Potassium Dichromate

Answer 1

The correct option is D

Acidified Potassium Dichromate

Explanation for correct option:

D. Acidified Potassium Dichromate

Reaction of Sulfur dioxide with acidified Potassium Dichromate:

• This reaction is used to test the presence of Sulfur dioxide gas.
• Sulfur dioxide gas turns acidified potassium dichromate(VI) solution from orange to green.
• When sulfur dioxide$\left({\mathrm{SO}}_2\right)$ reacts with acidified potassium dichromate$\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$, Chromium sulfate$\left({\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3\right)$ is formed along with Potassium sulfate$\left({\mathrm{K}}_2{\mathrm{SO}}_4\right)$ and water.
• The chemical reaction can be depicted as:

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\left(\mathrm{s}\right)+3{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)+{\mathrm{K}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Explanation for incorrect options:

Acidified Potassium Dichromate is used to test the presence of sulfur dioxide. Thus, options A, B, and C are incorrect.

Hence, the correct option is D i.e. Acidified Potassium Dichromate