Calculate the fraction of ethylene glycol (C₂H₆O₂) in a solution containing 20% of C₂H₆O₂ by mass.

Given $20\%\left(\frac{\mathrm{w}}{\mathrm{W}}\right)$ ethylene glycol solution
Let Wt of solution = 100g
Wt of ethylene glycol = 20g
$\therefore$ Wt of water = 100 – 20 = 80g
Number of moles of ${\mathrm{C}}_2{\mathrm{H}}_6{\mathrm{O}}_2=\frac{20 \mathrm{g}}{62 \mathrm{g}{ \mathrm{mol}}^{-1}}=0.322 \mathrm{mol}$
moles of water $=\frac{80\mathrm{g}}{18\mathrm{g}{ \mathrm{mol}}^{-1}}$ = 4.444mol
${\mathrm{X}}_{\mathrm{glycol}}=\frac{0.322 \mathrm{mol}}{0.322 \mathrm{mol}+4.444 \mathrm{mol}}=0.068$
Mole fraction of water can also be calculated as: 1 - 0.068 = 0.932