Question

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

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

Answer 1

Answer: (B)

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

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

$d=1.4g/c{m}^3$

Atomic mass $=56g/mol$

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

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

$n=20.1mol$