Question

If the van't Hoff factor for LiCl in a 0.62m solution is 1.92, what is the vapor pressure depression in mmHg of the solution at 298 K? (The vapor pressure of water at 298 K is 23.76 mmHg.)

Answer 1

Answer:

0.50mmHg

Explanation:

Raoult's law (Vapor pressure depression) is:

$P_{solution} = X_{solvent} P^0_{solvent}$

Where P is vapour pressure of solution and vapour pressure of solvent and X is mole fraction of solvent.

Van't Hoff factor helps to know how many species comes from the dissolution of the compound in the solvent.

Assuming volume of solution is 1L, moles of LiCl in solution are:

0.62×1.92 = 1.19 moles of LiCl in solution

Moles of water in 1L are:

1L ≡ 1000g × (1mol / 18g) = 55.56mol H₂O

Mole fraction of water is:

55.56mol / (55.56mol + 1.19mol) = 0.979

Vapour pressure of solution is:

$P_{solution} = 23.26mmHg$

That means vapour pressure depression is:

23.76mmHg - 23.26mmHg = 0.50mmHg

I hope it helps!