Question

An aqueous solution is 1.00 molal in Kl. Which change will cause the vapour pressure of the solution to increase?

Options

• Addition of NaCl

• Addition of Na₂SO₄

• Addition of 1.00 molal KI

• Addition of water

Answer 1

Addition of water

Explanation:

Vapour pressure of a solution is inversely related to solute concentration. Adding more solute (NaCl, Na₂SO₄, or even more KI) will increase the number of solute particles, thereby lowering the vapour pressure due to Raoult’s law. On the other hand, adding water dilutes the solution, reducing the mole fraction of solute and increasing the mole fraction of solvent, which raises the vapour pressure.