Question

Assertion :Concentrated $H_{2}S{O}_4$ reacts with $KCl$ to give $C{l}_2$ gas. Reason: $HCl$ cannot be oxidised by concentrated $H_{2}S{O}_4$.

• A. Both assertion and reason are CORRECT and reason is the CORRECT explanation of the assertion.
• B. Both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.
• C. Assertion is CORRECT, but reason is INCORRECT.
• D. Assertion is INCORRECT, but reason is CORRECT.

Answer 1

The correct option is D Assertion is INCORRECT, but reason is CORRECT.

$KCl$ and $H_{2}S{O}_4$ react to give only $HCl$ but not chlorine $C{l}_2$ gas, whereas $KI$ and $H_{2}S{O}_4$ react to liberate iodine (free halogen).
This is because $HBr$ and $HI$ are powerful oxidising agents, and they are also thermodynamically less stable than $HCl$. Thus easily dissociates to $H_2$ and $X_2$ (X=I/Br) at higher temperatures. And, conc. $H_{2}S{O}_4$ is a fairly effective oxidising agent.
The reaction involved is:
$2HX+H_{2}S{O}_4\to S{O}_2+X_2+2H_{2}O$ for $X=I/Br$
$HCl$ is only a mild reducing agent, and it is not easily oxidised to free chlorine gas by conc.$H_{2}S{O}_4$.
thus assertion is wrong and reason is correct.
option D is correct