Question

What is the mole fraction of water in 200g of 95 ethanol?

Answer 1

              If the solution is 95% by weight, that means that in 100 grams of solution you have 5 grams of water and 95 grams of ethanol.

Convert each of these masses to moles by dividing each mass by the molar mass of the compound.

5 g/18 g/mol = 0.278 mol water
95 g / 46g/mol = 2.065 mol ethanol

Mole fraction water:
= mol water / total moles
= 0.278/ (0.278 + 2.065)
= 0.119