Question

A 0.1m solution of K2SO4 in water has freezing point of -4.3degree Celsius. What is the value of van't hoff factor if kf for water is 1.86K kg mol inverse?

Answer 1

[Note: Either the value of molality is wrong or the value of freezing point is wrong.

There are two possibilities:

If Tf = - 4.3 °C, then m = 1 m

If m = 0.1, then Tf = -0.43 °C]

We are considering the first case. However, the answer would be same for both the cases]

Correct Solution:

Given:

m = 1 m

Tf = -4.3 °C

Kf = 1.86 K/kgmol

To Find:

The value of Van't hoff factor i.

Calculation:

- The depression in freezing point is given as:

ΔTf = i × Kf × m

⇒ T₀ - Tf = i × Kf × m

⇒ 0 - (-4.3) = i × 1.86 × 1

⇒ i = 4.3/1.86

⇒ i = 2.312

- So, the value of van't hoff factor for K2SO4 solution is 2.312.