JEE Main 2015 — Chemistry Physical Chemistry

2015mcqhard

At $298K$ , the standard reduction potentials are $1.51V$ for ${MnO}_{4}^{-} | M{n}^{2+}$ , $1.36V$ for $C{l}_{2}|C{l}^{-}$ , $1.07V$ for $B{r}_{2}|B{r}^{-}$ , $0.54V$ for ${I}_{2}|{I}^{-}$ . At $\mathrm{pH}=3$ , permanganate is expected to oxidize: $(\frac{RT}{F}=0.059)$

Official previous-year question

Held on 11 Apr 2015 · Verified 6 Jul 2026.

Options

A
$C{l}^{-}$ and $B{r}^{-}$
B
$B{r}^{-}$ and ${I}^{-}$
C
${I}^{-}$ only
D
$C{l}^{-} , B{r}^{-}$ and ${I}^{-}$

Did you get this right?

Solution

${MnO}_{4}^{-}+8{H}^{+}+5{e}^{-}\rightarrow M{n}^{2+}+4{H}_{2}O$

${E}_{\frac{{MnO}_{4}^{-}}{M{n}^{2+}}}={E}^{o}-\frac{0.059}{5}\mathrm{log}⁡\frac{[M{n}^{2+}]}{[{MnO}_{4}^{-}]{[{H}^{+}]}^{8}}$

$=1.51-\frac{0.059}{5}\mathrm{log}⁡\frac{1}{{[{10}^{-3}]}^{8}}$

(Assuming $[{MnO}_{4}^{-}]=[M{n}^{2+}]=1M$ )

$=1.51-\frac{0.059}{5}\times 24=1.51-0.28$

$=1.23 V$

${E}_{(red)(\frac{{MnO}_{4}^{-}}{M{n}^{2+}})}^{o}=1.23 V>{E}_{red\frac{B{r}_{2}}{B{r}^{-}}}^{o}>{E}_{red\frac{{I}_{2}}{{I}^{-}}}^{o}$

i.e. it will oxidise $B{r}^{-}$ and ${I}^{-}$ , only.

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JEE Main 2015 — Chemistry Physical Chemistry

2015mcqhard

Official previous-year question

Held on 11 Apr 2015 · Verified 6 Jul 2026.

Options

A
$C{l}^{-}$ and $B{r}^{-}$
B
$B{r}^{-}$ and ${I}^{-}$
C
${I}^{-}$ only
D
$C{l}^{-} , B{r}^{-}$ and ${I}^{-}$

Did you get this right?

Solution

${MnO}_{4}^{-}+8{H}^{+}+5{e}^{-}\rightarrow M{n}^{2+}+4{H}_{2}O$

${E}_{\frac{{MnO}_{4}^{-}}{M{n}^{2+}}}={E}^{o}-\frac{0.059}{5}\mathrm{log}⁡\frac{[M{n}^{2+}]}{[{MnO}_{4}^{-}]{[{H}^{+}]}^{8}}$

$=1.51-\frac{0.059}{5}\mathrm{log}⁡\frac{1}{{[{10}^{-3}]}^{8}}$

(Assuming $[{MnO}_{4}^{-}]=[M{n}^{2+}]=1M$ )

$=1.51-\frac{0.059}{5}\times 24=1.51-0.28$

$=1.23 V$

${E}_{(red)(\frac{{MnO}_{4}^{-}}{M{n}^{2+}})}^{o}=1.23 V>{E}_{red\frac{B{r}_{2}}{B{r}^{-}}}^{o}>{E}_{red\frac{{I}_{2}}{{I}^{-}}}^{o}$

i.e. it will oxidise $B{r}^{-}$ and ${I}^{-}$ , only.

Your note

JEE Main Physical Chemistry in other years

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JEE Main 2015 — Chemistry Physical Chemistry

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Solution

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JEE Main Physical Chemistry in other years

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JEE Main 2015 — Chemistry Physical Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry