Question

The addition of 100 g of a non-volatile unknown compound to 750 g CCl4 lowered the freezing point of the solvent by 10.5 K at 1 atm. The normal freezing point of pure CCl4 is 250 K and the molar enthalpy of fusion is 2.7 kJ/mol. Calculate the molar mass of the compound.

Answer 1

According to the depreassion in freezing point,

triangle Tf = Kf X m

Here,

Triangle Tf - the depreassion in freeing point

Kf - the molal depression constant

m - molality of the solution.

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Depression in freezing point of solution, tirangle Tf = 10.5K

Molal depression constant of CCI4 solvent Kf = 30.K/m

Molality of the solution, m = 0.350 m

= 0.350 mol/kg solvent

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mass of CCI4 solvent = 750 g = 0.750 Kg.