Question

Acidified potassium permanganate solution is decolourised by:

• A. Bleaching Powder
• B. White Vitriol
• C. Mohr's Salt
• D. Microcosmic salt

Answer 1

The correct option is C

Mohr's Salt

The explanation for the correct answer

option (C): Acidified potassium permanganate solution is decolourised by Mohr’s salt.

• Mohr’s Salt also referred to as ammonium iron(II) sulphate, is an inorganic compound whose chemical formula is represented as${\left({\mathrm{NH}}_4\right)}_2\mathrm{Fe}{\left({\mathrm{SO}}_4\right)}_2{\left({\mathrm{H}}_2\mathrm{O}\right)}_6$.
• The ferrous ion of Mohr's salt undergoes oxidation.

$\underset{\mathrm{potassium}\mathrm{permanganate}}{2{\mathrm{KMnO}}_4\left(\mathrm{aq}\right)}+\underset{sulphuricacid}{8H_{2}SO4\left(aq\right)}+\underset{ferroussulphate}{10FeS{O}_4\left(aq\right)}\to \underset{\mathrm{potassium}\mathrm{sulphate}}{\mathrm{K}2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{manganese}\mathrm{sulphate}}{2{\mathrm{MnSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{ferric}\mathrm{sulphate}}{5{\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{water}}{8{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}$

• Mohr's salt decolourises ${\mathrm{KMnO}}_4$ by reducing ${\mathrm{Mn}}^{7+}$ ions to ${\mathrm{Mn}}^{2+}$ ions.

The explanation for the incorrect answer

Option (A): Bleaching Powder: The chemical name of bleaching powder is calcium hypochlorite

• It is used for bleaching dirty clothes in the laundry and as a bleaching agent for cotton and linen in the textile industry.
• The chemical formula:$\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2$.

Option (B): The chemical formula of white vitriol is ${\mathrm{ZnSO}}_4.7{\mathrm{H}}_2{\mathrm{SO}}_4$.The chemical name of white vitriol is Zinc Sulphate.

White vitriol is used in the synthesis of the antibacterial drug. It is used as an absorbent.

Option (D): The formula for microcosmic salt is $\mathrm{Na}\left({\mathrm{NH}}_4\right){\mathrm{HPO}}_4$.

• The other name for microcosmic salt is sodium ammonium hydrogen phosphate.

Therefore, the correct option is (C) i.e., Acidified potassium permanganate solution $\left({\mathrm{KMnO}}_4\right)$ is decolourised by Mohr's Salt.