At 20.0 mL solution containing 0.2 g impure $\mathrm{H}_{2} \mathrm{O}_{2}$ reacts completely with 0.316 g of $\mathrm{KMnO}_{4}$ in acid solution. The purity of $\mathrm{H}_{2} \mathrm{O}_{2}$ (in %) is ____. (mol. wt. of $\mathrm{H}_{2} \mathrm{O}_{2}=34$; mol. wt. of $\mathrm{KMnO}_{4}=158$)

JEE Main · 2020 · 04 Sep 2020 · Shift 1 · Redox Reactions and Electrochemistry

At 20.0 mL solution containing 0.2 g impure

H_{2} O_{2}

reacts completely with 0.316 g of

KMnO_{4}

in acid solution. The purity of

H_{2} O_{2}

(in %) is ____.
(mol. wt. of

H_{2} O_{2} = 34

; mol. wt. of

KMnO_{4} = 158

)

Answer: 85

In acid medium permanganate oxidises hydrogen peroxide according to

2 MnO X_{4} X^{-} + 5 H X_{2} O X_{2} + 6 H X^{+} 2 Mn X^{2 +} + 5 O X_{2} + 8 H X_{2} O

. The equivalents of

KMnO X_{4}

used are

\frac{0.316}{158} \times 5 = 0.01

, since each mole supplies

5

equivalents in acid, and because the reaction is complete the

H X_{2} O X_{2}

supplies the same

0.01

equivalents. With

H X_{2} O X_{2}

having equivalent mass

\frac{34}{2} = 17

, the mass of pure

H X_{2} O X_{2}

0.01 \times 17 = 0.17

g. Against the

0.2

g taken, the purity is

\frac{0.17}{0.2} \times 100 = 85%

JEE Main · 2020 · 04 Sep 2020 · Shift 1 · Integer answer