Question

Place the solutions below in order of increasing freezing point, and explain the order:

.15 m (molality) CH3OH (methanol), .10 m NaCl (sodium chloride), .18 m CH3CH2OH (ethanol), .080 m Na2SO4 (sodium sulfate)

Answer 1

CH₃OH does not dissociate into ions. so it is 0.15 m - highest freezing point

NaCl dissociates into two ions. so it is 0.10 * 2 = 0.2 m

CH₃CH₂OH does not dissociate. so it is 0.18 m

Na₂SO₄ dissociates into three ions. so it is 0.080 * 3 = 0.24 m - lowest freezing point

As the molality increases freezing point decreases, so

Na₂SO₄(0.24 m) < NaCl(0.2 m) < CH₃CH₂OH(0.18 m) < CH₃OH(0.15 m)