When $10 m L$ of an aqueous solution of ${K M n O}_{4}$ was titrated in acidic medium, equal volume of $0.1 M$ of an aqueous solution of ferrous sulphate was required for complete discharge of colour. The strength of ${K M n O}_{4}$ in grams per litre is ____ $- 10^{- 2}$ . (Nearest integer)
[Atomic mass of $K = 39, M n = 55, O = 16$ ]

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answer is 3.16.

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Detailed Solution

Let molarity of ${K M n O}_{4} = x$

${K \overset{+ 7}{M n} O}_{4} + {\overset{+ 2}{F e} S O}_{4} \to {\overset{+ 3}{F e}}_{2} {({S O}_{4})}_{3} + {M n}^{2 +}$

(Equivalents of ${K M n O}_{4}$ reacted $) = ($ Equivalents of ${F e S O}_{4}$ reacted)

No. of equivalents=VM(n-factor)

$\Rightarrow (5 \times x \times 10 m l) = 1 \times 0.1 \times 10 m l \Rightarrow x = 0.02 M$

Molar mass of ${K M n O}_{4} = 158 g m / m o l$

$\Rightarrow S t r e n g t h = (x \times 158) = 3.16 g / ℓ$

Hence the correct answer is 3.16.

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