Question

What is the mole fraction of a nonelectrolyte in an aqueous solution above which the vapor pressure of water is 745 mm Hg at 100°C?

Answer 1

Answer:

Mole fraction of the nonelectrolyte is 0.020

Explanation:

To solve this question you need to use Raoult's law that states vapor pressure of a solvent above a solution is equal to the vapor pressure of the pure solvent times mole fraction of the solvent present. The formula is:

$P_{solution} = X P^0$

Where the pressure of the solution is 745mm Hg, X is mole fraction of the solvent and P° is the pressure of the pure solvent (760mm Hg). Replacing:

745 mmHg = X 760 mmHg

0.980 = X

In an aqueous solution of a nonelectrolyte, the mole fraction of water + mole fraction of nonelectrolyte = 1. As mole fraction of water is 0.980:

1 = 0.980 + Y -Where Y is mole fraction of nonelectrolyte.-

Y = 0.020

I hope it helps!

Answer 2

The mole fraction of a gaseous compound is equal to the ratio of the vapor pressure of the compound to the total pressure of the vessel. In this case, teh vapor pressure of tehe non-electrolyte is 760 - 745 = 15 mmHg. hence the mole fraction is 15 mm Hg / 760 mmHg equal to 0.0197