Question

Calculate the freezing point of a solution containing 0.5 g KCl (Molar mass =
74.5 g/mol) dissolved in 100 g water, assuming KCl to be 92% ionized.
Kfof water = 1.86 K kg / mol.

Answer 1

Explanation:

Given Calculate the freezing point of a solution containing 0.5 g KCl (Molar mass =  74.5 g/mol) dissolved in 100 g water, assuming KCl to be 92% ionized.  Kf of water = 1.86 K kg / mol.

• We know that I = calculated molar mass / theoretical molar mass
•                    1.92 = 74.5 / theoretical molar mass
• Theoretical molar mass = 38.802
• The depression in the freezing point is given by
•  So ΔTf = 1000 x Kf x W2 / M2 x W1
•                 = 1000 x 1.86 x 0.5 / 38.802 x 100
•                = 0.23 K
• Now freezing point of the solution is  
• So ΔTf = Initial freezing point – freezing point after addition of solute.
• So 0.23 = 0 – the freezing point after addition of solute.

Therefore freezing point of solution after adding KCl will be – 0.23 degree Celsius.

Answer 2

Given:

Given mass kcl =0.5

Molar mass=74.5

Alpa value 92%

Water given=100