Question

Calculate the molecular mass of:

Lead nitrate $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$.

Answer 1

Molecular mass:

• Molecular mass of a substance is the number of times a molecule of the substance is heavier than $\frac{1}{12}th$ of mass of a carbon ($\mathrm{C}-12$) atom.
• Molecular mass of a substance can be obtained by adding the atomic masses of all the atoms present in a molecule of the substance.

The molecular mass of Lead nitrate $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$:

$$\begin{gathered} =\text{Atomic mass of lead + 2×(atomic mass of nitrogen)+ 6×(atomic mass of oxygen)} \\ =207+2\times 14+6\times 16 \\ =331\text{a.m.u.} \end{gathered}$$

Therefore, the molecular mass of Lead nitrate $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$is $331\mathrm{a}.\mathrm{m}.\mathrm{u}.$