Question

Which pf the following solution has higher freezing point ? 0.05 M Al2(SO4)3 , 0.1 M K3[Fe(CN)6] justify.

Answer 1

2nd is lower due to greater vant hoff factor

Answer 2

The correct answer is - 0.05 M Al₂(SO₄)₃ has a higher freezing point.

Al₂(SO₄)₃ dissociates in water to give 5 mol of ions per mole of the compound.

The freezing point can be calculated using the formula - ΔTf = i * X, where i is the number of ions formed and X is the concentration.

So, ΔTf of 0.05 M Al₂(SO₄)₃ = 5 x 0.05 = 0.25 moles of ions

Similarly, for K₃[Fe(CN)₆], the number of ions formed on dissociation in water per mole of compound is, i = 4

ΔTf  of K₃[Fe(CN)₆] = 4 x 0.1 = 0.4 moles of ions

Since the Freezing point is directly proportional to the number of dissolved particles, it can be concluded that 0.05 M Al₂(SO₄)₃ has a higher freezing point than 0.1 M of K₃[Fe(CN)₆].