Question

Calculate the formula masses of the following compounds:
(a) Sodium oxide, Na₂O
(b) Aluminium oxide, Al₂O₃
(Given: Atomic Masses: Na = 23 u; O = 16 u; Al = 27 u)

Answer 1

(a) The formula mass of sodium oxide,
$$\begin{gathered} \mathrm{Formula}\mathrm{mass}\mathrm{of}{\mathrm{Na}}_2\mathrm{O}=2\times \mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Na}+\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{oxygen} \\ \mathrm{Formula}\mathrm{mass}\mathrm{of}{\mathrm{Na}}_2\mathrm{O}=2\times 23+16 \\ \mathrm{Formula}\mathrm{mass}\mathrm{of}{\mathrm{Na}}_2\mathrm{O}=62\mathrm{u} \end{gathered}$$

(b) The formula mass of aluminum oxide,
$$\begin{gathered} \mathrm{Formula}\mathrm{mass}\mathrm{of}{\mathrm{Al}}_2{\mathrm{O}}_3=2\times \mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{Al}+3\times \mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{oxygen} \\ \mathrm{Formula}\mathrm{mass}\mathrm{of}{\mathrm{Al}}_2{\mathrm{O}}_3=2\times 27+3\times 16 \\ \mathrm{Formula}\mathrm{mass}\mathrm{of}{\mathrm{Al}}_2{\mathrm{O}}_3=102\mathrm{u} \end{gathered}$$