Question

Permanganate titrations cannot be performed satisfactorily in presence of HCl. The reason is

• A. Both $\text{HCl}$ and $\text{KMnO}_4$ act as oxidising agents
• B. $\text{KMnO}_4$ is a weaker oxidising agent in presence of $\text{HCl}$
• C. $\text{KMnO}_4$ oxidises $\text{HCl}$ into $\text{Cl}_2$
• D. $\text{KMnO}_4$ acts as a reducing agent in the presence of $\text{HCl}$

Hint:

Use H$_2$SO$_4$ or HNO$_3$ for permanganate titrations to avoid Cl$^-$ oxidation. $\text{KMnO}_4$ oxidizes halides in acidic conditions. Check redox potentials to predict side reactions.

Answer 1

The Correct Option is C

1. In permanganate titrations, $\text{KMnO}_4$ acts as a strong oxidizing agent in acidic medium, reducing to Mn$^{2+}$.
2. Presence of HCl introduces Cl$^-$ ions, which $\text{KMnO}_4$ oxidizes to Cl$_2$ gas (2Cl$^-$ $\to$ Cl$_2$ + 2e$^-$), consuming some $\text{KMnO}_4$.
3. This side reaction interferes with the titration, reducing accuracy, as $\text{KMnO}_4$ is used up by HCl instead of the analyte.
4. Option (1) is incorrect: HCl is not an oxidizing agent. Option (2) is incorrect: $\text{KMnO}_4$ remains strong. Option (4) is incorrect: $\text{KMnO}_4$ is not a reducing agent.
5. Thus, the answer is (3) $\text{KMnO}_4$ oxidises $\text{HCl}$ into $\text{Cl}_2$.