Question

A spherical ball of radius $7 \,cm$ contains $56 \,w\%$ iron. Find out the number of moles of iron present approximately in the ball? $\left(d=1.4 \,g\, cm ^{-3} ;\right.$ atomic mass $=56 \,g\, mol ^{-1})$

• A. 15.1
• B. 20.1
• C. 25.1
• D. 35.1

Answer 1

Answer: (B)

$56 \,w \%$ iron spherical ball has radius $=7\, cm$

Volume $=\frac{4}{3} \pi r^{3}=\frac{4}{3} \times 3.14 \times(7 \times 7 \times 7)$

$ d =1.4 \,g / cm ^{3} $

Atomic mass $=56 \,g / mol$

$ n =\frac{d \times 10 \times mass \% \times \text { volume }}{\text { atomic mass } \times 1000} $

$n =\frac{1.4 g / cm ^{3} \times 10 \times 56 \times \frac{4}{3} \times 3.14 \times(7)^{3}}{56 \times 1000}$

$ n= 20.1 \,mol $