Some Basic Concepts of Chemistry - Result Question 32
Sujective Questions
32. Hydrogen peroxide solution $(20 mL)$ reacts quantitatively with a solution of $KMnO _4(20 mL)$ acidified with dilute $H _2 SO _4$. The same volume of the $KMnO _4$ solution is just decolourised by $10 mL$ of $MnSO _4$ in neutral medium simultaneously forming a dark brown precipitate of hydrated $MnO _2$. The brown precipitate is dissolved in $10 mL$ of $0.2 M$ sodium oxalate under boiling condition in the presence of dilute $H _2 SO _4$. Write the balanced equations involved in the reactions and calculate the molarity of $H _2 O _2$.
(2001)
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Solution:
$\begin{aligned} & \text { Meq of oxalate }=10 \times 0.2 \times 2=4 \\ & \text { Meq of } \mathrm{MnO}_2 \text { formed }=\mathrm{Meq} \text { of oxalate }=4 \\ & \text { Meq of } \mathrm{KMnO}_4 \text { in } 20 \mathrm{~mL}=4 \\ & \Rightarrow \quad \text { Normality of } \mathrm{H}_2 \mathrm{O}_2 \times 20=4 \\ & \Rightarrow \quad \text { Normality of } \mathrm{H}_2 \mathrm{O}_2=0.20 \mathrm{~N} \\ & \Rightarrow \quad \text { Molarity of } \mathrm{H}_2 \mathrm{O}_2=\frac{0.20}{2}=0.10 \mathrm{M} \\ & \end{aligned}$
The balanced reactions are
$\begin{aligned} 2 \mathrm{KMnO}_4+5 \mathrm{H}_2 \mathrm{O}_2+3 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow & 2 \mathrm{MnSO}_4+5 \mathrm{O}_2 \\ & +\mathrm{K}_2 \mathrm{SO}_4+8 \mathrm{H}_2 \mathrm{O} \\ \mathrm{MnO}_2+\mathrm{Na}_2 \mathrm{C}_2 \mathrm{O}_4+2 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{MnSO}_4 & +\mathrm{Na}_2 \mathrm{SO}_4 \\ & +2 \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O} \end{aligned}$
BETA
