What is the molar mass of iron $\left(\mathrm{III}\right)$ oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$?

Step 1: Molar mass:

• The mass of $1$ mole of a substance is called its molar mass.

Step 2: Formula for molar mass:

• $\mathrm{Molar}\mathrm{mass}=\mathrm{The}\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{element}\times \mathrm{number}\mathrm{of}\mathrm{atoms}\mathrm{given}\mathrm{in}\mathrm{subscript}$

Step 3: Calculation of Molar mass of iron $\left(\mathrm{III}\right)$ oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$:

$$\begin{gathered} \mathrm{Molar}\mathrm{mass}\mathrm{of}{\mathrm{Fe}}_2{\mathrm{O}}_3=\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{Fe}+\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{O} \\ \mathrm{Molar}\mathrm{mass}\mathrm{of}{\mathrm{Fe}}_2{\mathrm{O}}_3=\left(2\times 55.85\mathrm{g}{\mathrm{mol}}^{-1}\right)+\left(3\times 16.00\mathrm{g}{\mathrm{mol}}^{-1}\right) \\ \mathrm{Molar}\mathrm{mass}\mathrm{of}{\mathrm{Fe}}_2{\mathrm{O}}_3=111.7\mathrm{g}{\mathrm{mol}}^{-1}+48\mathrm{g}{\mathrm{mol}}^{-1}=159.7\mathrm{g}{\mathrm{mol}}^{-1} \end{gathered}$$

Thus, the molar mass of iron $\left(\mathrm{III}\right)$ oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ is $159.7\mathrm{g}{\mathrm{mol}}^{-1}$.