CBSE Class 12-science Answered

Benzene and toluene form a solution which is very nearly ideal. Consider a mixture of benzene (Bz) and toluene (Tol) at 60^o C. At 60^o C the vapor pressures of pure benzene and pure toluene are 385 Torr and 139 Torr, respectively. What are the vapor pressures of benzene and toluene in a mixture with X_Bz = 0.400, and X_Tol = 0.600, and what is the composition of the vapor in equilibrium with this solution?

Use Raoult's law to find the vapor pressures of the two species,

The total pressure is the sum of these two individual pressures, 237 Torr.

The composition of the vapor phase is obtained from the vapor pressures and Dalton's law of partial pressures, That is, there is no heat involved in the mixing of ideal solutions. If we mix several components and the mixture gets hot or cold we can be sure that the solution formed was not ideal.