Chemistry Freezing point???

Question

Which of the following has a lower freezing pont: 1 molal aqueous sodium chloride or 1 molal aqueous glucose solution? Why?

Answer 1

Step 1 :

Freezing point : , where

is the van 't Hoff factor,

is the molality of the solution and

is the molality depression constant.

for is 1.86 .

Freezing point : .

Step 2 :

Find freezing point of 1 molal aqueous sodium chloride.

Molality of sodium chloride is 1 molal.

Here, for sodium chloride is 2.

Freezing point : .

Substitute = 2, and in above equation.

.

New freezing point of sodium chloride solution is .

Freezing point of 1 molal aqueous sodium chloride solution is .

Step 3 :

Find freezing point of 1 molal aqueous glucose.

Molality of glucose is 1 molal.

Freezing point : .

Here, for glucose is 3.

Substitute and in above equation.

.

New freezing point of glucose solution is .

Freezing point of 1 molal aqueous glucose solution is .

Step 4 :

Observe the above calculations.

1 molal aqueous glucose has the lower freezing point when compare to 1 molal aqueous sodium chloride.

Solution :

1 molal aqueous glucose has the lower freezing point when compare to 1 molal aqueous sodium chloride.