Question

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040.

[Take the volume of solution as a volume of water]

Answer 1

Let total moles be 1.

Number of moles of ethanol $=0.04$

Number of moles of water $=1-0.04=0.96$

Mass of water $=0.96\times 18=17.3g\approx 17.3ml$ [since density of water $=1g/ml$]

Hence, Molarity $=\frac{n}{V}=\frac{0.040}{0.0173}=2.31M$