Question 1

What is Raoult's Law?

Accepted Answer

Raoult's Law states that the vapor pressure of a solution equals the mole fraction of the solvent times the vapor pressure of the pure solvent: P = x × P°. Adding solute always lowers the vapor pressure.

Question 2

What is an ideal solution?

Accepted Answer

An ideal solution perfectly obeys Raoult's Law. The solute-solvent interactions are the same strength as solvent-solvent and solute-solute interactions. Most real solutions show deviations.

Question 3

What is vapor pressure lowering?

Accepted Answer

ΔP = x_solute × P°. The decrease in vapor pressure is proportional to the mole fraction of the solute. This is a colligative property -- it depends only on the number of solute particles, not their identity.

Question 4

Does Raoult's Law work for electrolytes?

Accepted Answer

For electrolytes, you must account for dissociation using the van't Hoff factor (i). NaCl produces 2 particles, so its effective mole fraction of solute particles is doubled.

Raoult's Law Calculator

Frequently Asked Questions