Question:
The mass of one steel screw is $4.11 \mathrm{~g}$. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth $\left(5.98 \times 10^{24} \mathrm{~kg}\right)$. Which one of the two is heavier and by how many times?
Solution:
No. of steel screws in 1 mole $=6.022 \times 10^{23}$
Mass of one steel screw $=4.11 \mathrm{~g}$
Mass of one mole steel screws $=(4.11 \mathrm{~g}) \times\left(6.022 \times 10^{23}\right)$
$=2.475 \times 10^{24} \mathrm{~g}=2.475 \times 10^{21} \mathrm{~kg}$
Mass of earth $=5.98 \times 10^{24} \mathrm{~kg}$ (Given)
$\frac{\text { Mass of earth }}{\text { Mass of steel screws }}=\frac{\left(5.98 \times 10^{24} \mathrm{~kg}\right)}{\left(2.475 \times 10^{21} \mathrm{~kg}\right)}=2.4 \times 10^{3}$