Question

3.92 g of ferrous ammonium sulphate crystals are dissolved in 100 ml of water, 20 ml of this solution requires 18 ml of KMnO₄ during titration for complete oxidation. The weight of KMnO₄ present in one litre of the solution is

(a) 3.476 g

(b) 12.38 g

(c) 34.76 g

(d) 1.238 g

Answer 1

Correct option is (a) 3.476 g

Normality of salt solution = \(\frac{3.92}{392} \times \frac 1{100} \times 1000 = 0.1 N\)

20 ml of 0.1 N salt solution \(\equiv\) 18 ml of KMnO₄ solution

\(\therefore\) Normality of KMnO₄ solution = \(\frac {20 \times 0.1}{18} = \frac 19 N\)

\(\therefore\) Strength of KMnO₄ solution = \(\frac 19 \times 31.6 = 3.5 g L^{-1}\)