Question

The boiling water of a 0.143 molal aqueous solution of MgCl2 is measured to be 100.639 C. Determine the van't Hoff factor for this salt . [Note: The boiling point elevation constant for water is 1.86 C Kg/ mol

Answer 1

Answer: van't Hoff factor for this salt is 2.402

Calculations:

Step 1: The boiling-point elevation can be calculated by the formula;

..........................(1)

Where, = boiling point elevation;

Or, = Boiling point of solution (T_b) - Boiling point of water (T_b⁰);

= van't Hoff factor;

= boiling point elevation constant;

and is the molality of the solution.

Step 2: Given data:

= 1.86 ^oC.Kg/mol

= 0.143 molal or 0.143 kg/mol;

Boiling point of MgCl₂ solution = T_b​ = 100.639 ^oC;

Boiling point of water = T_b⁰​ = 100.0 ^oC;

= 100.639 ^oC − 100 ^oC = 0.639 ^oC.

And = ?

Step 3: Putting the all values in equation (1) we get,

Hence, van't Hoff factor for this salt is 2.402.