Question

What is the mass of $0.5$ mole of water molecules?

Answer 1

Step 1: Given information

• Moles of water $\left({\mathrm{H}}_2\mathrm{O}\right)$ molecules$=0.5\mathrm{mol}$

Step 2: Formula to calculate mass

$\mathrm{m}=\mathrm{n}\times \mathrm{M}$

• $\mathrm{m}$ is the mass.
• $\mathrm{n}$ is the number of moles.
• $\mathrm{M}$ is the molar mass.

Step 3: Determine the mass of oxygen atom

• Molar mass of water molecule $=18\mathrm{g}{\mathrm{mol}}^{-1}$
• The mass of water molecule is as follows:

$\begin{array}{rcl}\mathrm{m}& =& \mathrm{n}\times \mathrm{M}\\ & =& 0.5\bcancel{\mathrm{mol}}\times 18\mathrm{g}\bcancel{{\mathrm{mol}}^{-1}}\\ & =& 9.0\mathrm{g}\end{array}$

Therefore, the mass of $\mathbf{0}\mathbf{.}\mathbf{5}$ mole of water molecules is $\mathbf{9}\mathbf{.}\mathbf{0}\mathbf{}\mathbf{g}$.