Question:
Calculate the number of moles of magnesium present in a magnesium ribon weighing $12 \mathrm{~g}$. Molar atomic mass of magnesium is $24 \mathrm{~g} \mathrm{~mol}^{-1}$.
Solution:
Mass of magnesium $(\mathrm{Mg})=12 \mathrm{~g}$
Molar atomic mass of magnesium $(\mathrm{Mg})=24 \mathrm{~g} \mathrm{~mol}^{-1}$.
No. of moles of magnesium $(\mathrm{Mg})=\frac{(\text { Mass })}{(\text { Molar atomic mass })}=\frac{(12 \mathrm{~g})}{\left(24 \mathrm{~g} \mathrm{~mol}^{-1}\right)}=0.5 \mathrm{~mol}$