Some Basic Concepts of Chemistry 2 Question 32
32. Hydrogen peroxide solution $(20 \mathrm{~mL})$ reacts quantitatively with a solution of $\mathrm{KMnO}{4}(20 \mathrm{~mL})$ acidified with dilute $\mathrm{H}{2} \mathrm{SO}{4}$. The same volume of the $\mathrm{KMnO}{4}$ solution is just decolourised by $10 \mathrm{~mL}$ of $\mathrm{MnSO}{4}$ in neutral medium simultaneously forming a dark brown precipitate of hydrated $\mathrm{MnO}{2}$. The brown precipitate is dissolved in $10 \mathrm{~mL}$ of $0.2 \mathrm{M}$ sodium oxalate under boiling condition in the presence of dilute $\mathrm{H}{2} \mathrm{SO}{4}$. Write the balanced equations involved in the reactions and calculate the molarity of $\mathrm{H}{2} \mathrm{O}{2}$.
(2001)
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Solution:
- Meq of oxalate $=10 \times 0.2 \times 2=4$
$\mathrm{Meq}$ of $\mathrm{MnO}_{2}$ formed $=$ Meq of oxalate $=4$
Meq of $\mathrm{KMnO}_{4}$ in $20 \mathrm{~mL}=4$
$\Rightarrow \quad$ Normality of $\mathrm{H}{2} \mathrm{O}{2} \times 20=4$
$\Rightarrow \quad$ Normality of $\mathrm{H}{2} \mathrm{O}{2}=0.20 \mathrm{~N}$
$\Rightarrow \quad$ Molarity of $\mathrm{H}{2} \mathrm{O}{2}=\frac{0.20}{2}=0.10 \mathrm{M}$
The balanced reactions are
$$ \begin{aligned} & 2 \mathrm{KMnO}{4}+5 \mathrm{H}{2} \mathrm{O}{2}+3 \mathrm{H}{2} \mathrm{SO}{4} \longrightarrow 2 \mathrm{MnSO}{4}+5 \mathrm{O}{2} \ & +\mathrm{K}{2} \mathrm{SO}{4}+8 \mathrm{H}{2} \mathrm{O} \ & \mathrm{MnO}{2}+\mathrm{Na}{2} \mathrm{C}{2} \mathrm{O}{4}+2 \mathrm{H}{2} \mathrm{SO}{4} \longrightarrow \mathrm{MnSO}{4}+\mathrm{Na}{2} \mathrm{SO}{4} \ & +2 \mathrm{CO}{2}+2 \mathrm{H}_{2} \mathrm{O} \end{aligned} $$
