Question

3.92 g of ferrous ammonium sulphate reacts completely with 50 ml of \(\frac{N}{10}\) KMnO\(_4\) solution. The percentage purity of the sample is:

• A. 50
• B. 78.4
• C. 80
• D. 39.2

Hint:

Ferrous ammonium sulphate has equivalent weight 392.

Answer 1

The Correct Option is B

Step 1: Normality relation: \[ N_1V_1 = N_2V_2 \]
Step 2: \[ \text{Equivalents of KMnO}_4 = \frac{1}{10}\times\frac{50}{1000}=0.005 \]
Step 3: Mass of pure salt required = \(0.005 \times 392 = 1.96\,\text{g}\)
Step 4: \[ \%\text{ purity}=\frac{1.96}{2.5}\times100=78.4\% \]