Question

Calculate the molecular mass of:

Ammonium sulphate ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$.

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 Ammonium sulphate ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$:

$$\begin{gathered} =2\times (\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{nitrogen})+8\times (\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{hydrogen})+\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{sulphur}+4\times (\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{oxygen}) \\ =2\times 14+8\times 1+32+4\times 16 \\ =28+8+32+64 \\ =132\mathrm{a}.\mathrm{m}.\mathrm{u}. \end{gathered}$$

Therefore, the molecular mass of Ammonium sulphate is $132\text{a.m.u.}$