Question

30. When 2.5 g of a sample of Mohr's salt reacts
completely with 50 mL of KMnO4 solution.
The % purity of the sample of Mohr's salt is:
46)78.4 .
(4) 40
(2) 70
(3) 37​

Answer 1

Answer:

Option (a) 78.4%

Explanation:

The complete question is:

When 2.5 g of a sample of Mohr's salt reacts  completely with 50 mL of N/10 KMnO4 solution.  The % purity of the sample of Mohr's salt is

(1) 78.4 .

(2) 70

(3) 37​

(4) 40

Solution:

Molecular weight of Mohr's salt (Ferrous Ammonium Sulphate) is 392 g/mole

Considering the solution to be 1 Litre and its weight to be x

Normality of the Mohr's Salt N₁ = (x/392) × (1/1) = x/392

It reacts with 50 mL N/10 KMnO₄

Thus,

using N₁V₁ = N₂V₂

$\frac{x}{392}\times 1000=50\times \frac{1}{10}$

$\implies x=0.392\times5=1.96$

Thus in 2.5 g, the actual Mohr's salt is only 1.96 g

%purity = $\frac{1.96}{2.5}\times 100$

            = 78.4 %

Hope this is helpful.