Question

Calculate the number of moles present in $9\mathrm{g}$ of ethane.

Answer 1

Step 1: Analyse the formula to calculate the number of moles.

• The number of moles can be calculated by using the formula:

$\mathrm{Number}\mathrm{of}\mathrm{moles}=\frac{\mathrm{Given}\mathrm{mass}}{\mathrm{Molar}\mathrm{mass}}$

• According to the question, the given mass is $9\mathrm{g}$ and the molecular mass can be calculated.

Step 2: Calculate the molecular mass of ethane.

• To find the molecular mass, we will add the atomic masses of all of the atoms in the molecule.
• In this case, the molar mass of ethane (${\mathrm{C}}_2{\mathrm{H}}_6$) can be calculated as:

$$\begin{gathered} \mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{C}}_2{\mathrm{H}}_6=(2\times \mathrm{C})+(6\times \mathrm{H}) \\ =(2\times 12)+(6\times 1) \\ =24+\hspace{0.17em}6=30\mathrm{g}{\mathrm{mol}}^{-1} \end{gathered}$$

• So, the molecular mass of ethane $=30\mathrm{g}{\mathrm{mol}}^{-1}$

Step 3: Calculate the number of moles.

• The given mass is $9\mathrm{g}$ and the molar mass is $30\mathrm{g}{\mathrm{mol}}^{-1}$
• So, the number of moles of ethane are $\frac{9\mathrm{g}}{30\mathrm{g}{\mathrm{mol}}^{-1}}=0.3\mathrm{moles}$

Hence, the number of moles present in $9\mathrm{g}$ of ethane is $0.3\mathrm{moles}$.