209. Draw a suitable labelled diagram to express the relationships for ideal solutions of A and B between vapour pressures and mole-fractions of components at constant temperature.

Answer:

(i) The solutions which obey Raoult’s law over the entire range of concentration are known as ideal solutions. The ideal solutions have two other important properties. The enthalpy of mixing of the pure components to form the solution is zero and the volume of mixing is also zero, i.e.,

Δ_mixH = 0
Δ_mixV = 0

It means that no heat is absorbed or evolved when the components are mixed. Also, the volume of solution would be equal to the sum of
volumes of the two components.

(ii) 

At molecular level, ideal behaviour of
the solutions can be explained by considering two components A and B. In pure components, the intermolecular attractive interactions will
be of types A-A and B-B, whereas in the binary solutions in addition to these two interactions, A-B type of interactions will also be present.
If the intermolecular attractive forces between the A-A and B-B are nearly equal to those between A-B, this leads to the formation of ideal
solution.
example: Solution of n-hexane and n-heptane, bromoethane and chloroethane, benzene and toluene, etc.


Escaping tendency of 'A' and 'B' should be same in pure liquids and in the solution.