Question

A vessel fitted with a weightless, frictionless piston of 0.025 $m^2$ area contains conc. HCl. The piston moved 1 in outward when 0.075 kg of iron fillings were added at 300 K. The solution left, behind was found to contain Fen. The approximate purity of the iron sample is:

• A. 50%
• B. 75%
• C. 90%
• D. 40%

Answer 1

The correct option is B 75%

Volume of $H_2$ gas produced $0.025\times 1=0.025m^3$ $=25L$

$PV=nRT$
$1\times 25=n\times 0.082\times 300$
${}^n{H}_2=1.016$
The balanced chemical reaction involved in the process is:
$Fe+2HCl\to FeC{l}_2+H_2\uparrow$
Thus, number of moles of iron will be $\mathrm{1.016.}$
i.e., Mass of iron $1.016\times 56$ i.e., $56.896g$
% purity of iron sample $\frac{56.896}{75}\times 100\approx 75$%