Question

A $0.46$ g sample of $A{s}_2{O}_3$ required $25.0$ mL of $KMn{O}_4$ solution for its titration. The molarity of $KMn{O}_4$ solution is :

• A. $0.016$
• B. $0.074$
• C. $0.032$
• D. $0.128$

Answer 1

The correct option is B $0.074$

The redox changes that occurs are as follows:

$A{s}_2{O}_3\to 2As{O}_4^{3-}+4e^{-}$
$5e^{-}+Mn{O}_4^{⊝}\to M{n}^{2+}$

$EwofA{s}_2{O}_3=\frac{2\times 75+3\times 16}{4}=\frac{198}{4}$

$A{s}_2{O}_3\equiv Mn{O}^{⊝}$
$mEq\equiv mEq$
$\left(\frac{0.46}{\frac{198}{4}}\right)\times {10}^3\equiv 25\times N$ $⟹N=0.037$

$M_{KMn{O}_4}=\frac{N}{5}=\frac{0.037}{5}=0.074$