The normal freezing point of a certain liquid

X

is

0.4°C

, but when

5.90g

of urea

NH22CO

are dissolved in

450.g

of

X

, it is found that the solution freezes at

−0.5°C

instead. Use this information to calculate the molal freezing point depression constant

Kf

of

X

.
Be sure your answer has the correct number of significant digits.

Answer : The molal freezing point depression constant of liquid X is,

Explanation :  Given,

Mass of urea (solute) = 5.90 g

Mass of liquid X (solvent) = 450 g  = 0.450 kg

Molar mass of urea = 60 g/mole

Formula used :  

where,

= change in freezing point

= freezing point of solution =

= freezing point of liquid X =

i = Van't Hoff factor = 1 (for non-electrolyte)

= Molal-freezing-point-depression constant = ?

m = molality

Now put all the given values in this formula, we get

Therefore, the molal freezing point depression constant of liquid X is,