Question 9 of 171

The molar volume of liquid benzene (density= 0.877 g ml-1) increases by a factor of 2750 as it vapourises at 20°C. At 27°C when a non-volatile solute (that does not dissociate) is dissolved in 54.6cm3 of benzene, vapour pressure of this solution, is found to be 98.88 mm Hg. calculate the freezing point of the solution.

Given: Enthalpy of vapourisation of benzene(l)=394.57 Jg-1. Enthalpy of fusion of benzene (l) = 10.06 kJ mol-1 Molal depression constant for benzene=5.0 K kg mol-1.

(a) 177.65 K

(b) 277.65 K

(c) 517.65 K

(d) 237.15 K