Discussion Forum

1)

A spherical ball of radius 7 cm contains 56 w% iron. Find out the number of moles of iron present approximately in the ball? 

(d=1.4 g cm^-3,  atomic mass =56 g mol^-1)

Answer:

Option B

Explanation:

 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/cm³

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

  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

Hence , option (b) is correct.