Question

Assertion :$H_{2}S$ reacts with oxygen under standard conditions in acid medium to give $H_{2}O$ and sulphur. Reason: $E_{H^{+}/O_2/Pt}^o>E_{H^{+}/H_{2}S/S}^o$

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is C Assertion is correct but Reason is incorrect

The half cell reactions and the net cell reaction are given below.

$2H^{+}+\frac{1}{2}{O}_2+2e\to H_{2}O;E_{RP}^o=A$
$H_{2}S\to 2H^{+}+S+2e;E_{OP}^o=B$
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$H_{2}S+\frac{1}{2}{O}_2\to H_{2}O+S$
The expression for the standard cell potential is $E_{cell}^o=E_{O{P}_{H_{2}S/H^{+}/S}}^o+E_{R{P}_{H^{+}/O_2/Pt}}^o$.

But, $E_{R{P}_{H^{+}/O_2/Pt}}^o>E_{R{P}_{H^{+}/H_{2}S/S}}^o$

Hence, $E_{cell}^o$ is positive.