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Q.
$3.92 \,g / L$ of a sample of ferrous ammonium sulphate reacts completely with $50\, mL \frac{N}{10} K MnO _{4}$ solution. The percentage purity of the sample is
BHUBHU 2010
Solution:
$\underset{\text {(Ferrous ammonium sulphate) })}{N_{1} V_{1}}=\underset {\left( KMnO _{4}\right) }{N _{2} V _{2}}$
$N_{1} \times 1000=\frac{1}{10} \times 50$
$N_{1}=\frac{50}{10^{4}}=\frac{1}{200}$
Eq. wt. of $FeSO _{4} .\left( NH _{4}\right)_{2} SO _{4} .6 H _{2} O$
$=$ mol. $w t .=392$
$\therefore $ Strength of pure salt
$=392 \times \frac{1}{200}$
$=1.96\, g L^{-1}$
$\therefore \%$ purity
$=\frac{1.96}{3.92} \times 100=50\%$