Question

$3.92\,g$ of ferrous ammonium sulphate react completely with $50\, ml \frac{N}{10} KMnO_{4}$ solution. The percentage purity of the sample is

• A. 50
• B. 78.4
• C. 80
• D. 39.2

Answer 1

Answer: (A)

50

Answer 2

$Eq$ of $KMnO _{4}$ used $=\frac{50 \times 1}{1000 \times 10}=0.005$
$\therefore$ Eq of FAS reacted $=0.005$
$\therefore$ weight of FAS needed
$=0.005 \times 392=1.96\, g$
Thus percentage purity of FAS is $50 \%$