Question

What is mole percent? Give an example

Answer 1

Mole percent:

• Mole percent ($\mathrm{mol}\%$) is the same as mole fraction in chemistry, but in a different guise.
• Multiplying the mole fraction by 100 yields the mole percentage of the given component.
• $\mathrm{Mole}\mathrm{Fraction}=\frac{\mathrm{the}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{one}\mathrm{ingredient}\mathrm{in}\mathrm{the}\mathrm{given}\mathrm{mixture}}{\mathrm{the}\mathrm{total}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{in}\mathrm{the}\mathrm{mixture}}.$
• As a result, Mole percent Equals Mole fraction x 100.
• $\mathrm{Mole}\mathrm{percent}=\frac{\mathrm{the}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{one}\mathrm{ingredient}\mathrm{in}\mathrm{the}\mathrm{given}\mathrm{mixture}}{\mathrm{the}\mathrm{total}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{in}\mathrm{the}\mathrm{mixture}}\times 100$

Example of mole percent:

• In an aqueous solution containing $25.0\mathrm{g}$ water and $5.0\mathrm{g}$ sodium chloride, finding the mole percentage of sodium chloride

Step 1: Finding the mole fraction of $\mathrm{NaCl}$

• no. of moles of $\mathrm{NaCl}$ =$\frac{\mathrm{given}\mathrm{mass}\mathrm{of}\mathrm{NaCl}}{\mathrm{molar}\mathrm{mass}\mathrm{of}\mathrm{NaCl}}=\frac{5\mathrm{g}}{58.5\mathrm{g}{\mathrm{mol}}^{-1}}=0.086\mathrm{mol}$
• no. of moles of ${\mathrm{H}}_2\mathrm{O}$ =$\frac{\mathrm{given}\mathrm{mass}\mathrm{of}{\mathrm{H}}_2\mathrm{O}}{\mathrm{molar}\mathrm{mass}\mathrm{of}{\mathrm{H}}_2\mathrm{O}}=\frac{25\mathrm{g}}{18\mathrm{g}{\mathrm{mol}}^{-1}}=1.388\mathrm{mol}$
• $$\begin{gathered} \mathrm{Mole}\mathrm{Fraction}=\frac{\mathrm{no}.\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{NaCl}}{\mathrm{no}.\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{NaCl}+\mathrm{no}.\mathrm{of}\mathrm{moles}\mathrm{of}{\mathrm{H}}_2\mathrm{O}} \\ \mathrm{Mole}\mathrm{Fraction}=\frac{0.086\mathrm{mol}}{0.086\mathrm{mol}+1.388\mathrm{mol}} \\ \mathrm{Mole}\mathrm{Fraction}=0.058 \end{gathered}$$

Step 2: Finding the mole percentage of $\mathrm{NaCl}$

• $$\begin{gathered} \mathrm{Mole}\mathrm{percent}\mathrm{of}\mathrm{NaCl}=\mathrm{Mole}\mathrm{fraction}\mathrm{of}\mathrm{NaCl}\mathrm{x}100. \\ \mathrm{Mole}\mathrm{percent}\mathrm{of}\mathrm{NaCl}=0.058\times 100 \\ \mathrm{Mole}\mathrm{percent}\mathrm{of}\mathrm{NaCl}=5.8\% \end{gathered}$$

Hence mole percentage of $\mathrm{NaCl}$ is $5.8\raisebox{1ex}{$\mathrm{o}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{o}$}\right.$