Question

Normal freezing point of a solvent is 15°C. A 0.5 molal solution of urea in the above solvent causes a freezing point depression of two degrees. Calculate the molal depression constant.​

Answer 1

Answer: $4^0C/m$

Explanation:

Depression in freezing point is given by ;

$\Delta T_f=i\times k_f\times m$

$\Delta T_f=T_f^0-T_f$ =  Depression in freezing point

i = Van'T Hoff factor  

$k_f$ = molal freezing point constant

m = molality

For urea, i= 1 as it is a non electrolyte and does not dissociate.

$2^0C=1\times k_f\times 0.5$

$k_f=4^0C/m$

Thus the value for the molal depression constant is $4^0C/m$

Answer 2

molal depression constant is 4 cm^-1