Question

Name a substance that oxidises concentrated \[{\text{HCl}}\] to chlorine
A. Manganese dioxide
B. Potassium permanganate
C. Sodium chloride
D. None of these

Answer 1

Hint: We must know that the potassium permanganate and manganese dioxide both are oxidizing agents. Both the reagents have the capability to oxidize \[{\text{HCl}}\] to chlorine gas.

Complete answer:
Manganese dioxide reacting with hydrochloric acid undergoes a redox reaction. \[{\text{M}}{{\text{n}}^{{\text{4 + }}}}\] in manganese dioxide is reduced to \[{\text{M}}{{\text{n}}^{{\text{2 + }}}}\] whereas, \[{\text{C}}{{\text{l}}^{\text{ - }}}\]in hydrochloric acid is oxidised to\[{\text{Cl}}\]. Hence, manganese dioxide in reaction with hydrochloric acid produces manganese chloride, water and chlorine gas.
Potassium permanganate reacts with hydrogen chloride to produce manganese (II) chloride, chlorine, potassium chloride, and water.
\[
  {\text{Mn}}{{\text{O}}_{{\text{2}}}}{\text{ + 4HCl}} \to {\text{MnC}}{{\text{l}}_{\text{2}}}{\text{ + 2H}}{}_{\text{2}}{\text{O + C}}{{\text{l}}_{{\text{2}}}} \uparrow \\
  {\text{2KMn}}{{\text{O}}_{\text{4}}}{\text{ + 16HCl}} \to {\text{2MnC}}{{\text{l}}_{\text{2}}}{\text{ + 2KCl + 8}}{{\text{H}}_{\text{2}}}{\text{O + 5C}}{{\text{l}}_{\text{2}}} \uparrow \\
 \]
Therefore, both A. Manganese dioxide and B. Potassium permanganate oxidizes concentrated \[{\text{HCl}}\] to chlorine.
Thus, both A and B are correct.

Additional Information:
Solid potassium permanganate if used it decomposes when heated:
\[{\text{2 KMn}}{{\text{O}}_{\text{4}}}{\text{}} \to {\text{ }}{{\text{K}}_{\text{2}}}{\text{Mn}}{{\text{O}}_{\text{4}}}{\text{ + Mn}}{{\text{O}}_{\text{2}}}\left( {\text{s}} \right){\text{ + O}}\]
Here, the oxidation state of manganese changes as in the potassium permanganate (oxidation state +7) to potassium manganate (oxidation state +6) and manganese dioxide (oxidation state +4). This could also have oxidising action.

Note:
We must know that chlorine gas is a yellow-greenish dense gas with a choking smell. It kills bacteria and hence it is used as a disinfectant. It is widely used in the treatment of drinking water and swimming pool water. It is a highly demanding product in industry as hundreds of consumer products from paper to paints, and from textiles to insecticides are being produced from chlorine gas.