Question

How the presence of ${\mathrm{SO}}_2$ is detected?

Answer 1

Detection of ${\mathrm{SO}}_2$:

• ${\mathrm{SO}}_2$​ is known to be a colorless and pungent-smelling gas.
• It can be detected by using a Potassium permanganate solution.
• When ${\mathrm{SO}}_2$ is made to pass through an acidified Potassium permanganate solution having a pink-violate color, it decolorizes the solution as it reduces ${\mathrm{MnO}}^{4-}$ions to ${\mathrm{Mn}}^{2+}$ ions giving out a suffocating smell that indicates its presence.
• The balanced chemical reaction for the above reaction can be given as;

$\underset{(\mathrm{Sulfer}\mathrm{Dioxide})}{5{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{(\mathrm{pink}-\mathrm{Violate})}{\underset{(\mathrm{Potassium}\mathrm{permanganate}\mathrm{ion})}{2{\mathrm{MnO}}^{4-}}}+\underset{\left(\mathrm{Water}\right)}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{Sufate}\mathrm{ion})}{5{{\mathrm{SO}}_4}^{2-}}+\underset{\mathrm{Hydrogen}\mathrm{ion}}{4{\mathrm{H}}^{+}}+\underset{\left(\mathrm{colorless}\right)}{\underset{(\mathrm{Manganate}\mathrm{ion})}{2{\mathrm{Mn}}^{2+}}}$

Therefore, in the above way, we can detect the presence of the gas ${\mathrm{SO}}_2$ gas.