Question

A sample of iron ore, weighing $0.700g$, is dissolved in nitric acid. The solution is then diluted with water, following with sufficient concentrated aqueous ammonia, to quantitative precipitation the iron as $Fe(OH{)}_3$. The precipitate is filtered, ignited and weighed as $F{e}_2{O}_3.$ If the mass of the ignited and dried precipitate is $0.541g$. What is the mass per cent of iron in the original iron ore sample?

$[Fe=56]$

• A. $27.0\%$
• B. $48.1\%$
• C. $54.1\%$
• D. $81.1\%$

Answer 1

Answer: (C)

$54.1\%$

$0.700g$ sample of iron are is converted to $Fe(OH{)}_3$ precipitate and ignited to form $F{e}_2{O}_3$.

Mass of $F{e}_2{O}_3$ obtained $=0.54/g$

$160gF{e}_2{O}_3$ contans $2Fe$

$160gF{e}_2{O}_3$ contains $112/gFe$

$0.541gF{e}_2{O}_3$ will contains $\frac{112\times 0.541}{160}$

$=0.3787gFe$

$\%$ Fe in sample $=\frac{0.3787}{0.700}\times 100$

$=54.1$ %

$\%Fe=54.1\%$

Hence, the correct option is $C$