Question

Which of the following aqueous solutions will have the highest boiling point?

		0.10 m KOH
		0.10 m RbCl
		0.05 m CaSO4
		0.05 m BaCl2
		0.10 m K2SO4

Answer 1

Elevation of Boiling Point of solution is a colligative property and thus it depends on no. of solute particles alone and not nature of solute particles.

KOH will dissociate into K+ and OH-, and thus in 1kg of water there will be 0.1 mol of K+ and 0.1 mol OH-, thus total 0.2 mol of solute particles in 1kg water.

Similarly RbCl wil have 0.2 mol of solute particles in 1kg water.

CaSO4 wil have 0.1 mol (0.05 mol Ca²⁺ + 0.05 mol SO₄^2-) of solute particles in 1kg water.

BaCl2 will have 0.15 mol {0.05 mol Ba²⁺ + (0.05 X 2) mol Cl^-}  of solute particles in 1kg water.

K2SO4 will have 0.3 mol {(0.1 X 2) mol K⁺ + 0.1 mol SO₄^-}  of solute particles in 1kg water.

Since 0.1 m K2SO4 has mximum no. of solute particles and thus have highest boiling point.