244. State and explain Raoult’s law. How would you distinguish between an ideal and non-ideal solution?

Answer:

Raoult's law state that for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction.

p₁ ∝ x₁

and p₁ = ${\mathrm{p}}_1^0$x₁

The proportionality constant is equal to the vapour pressure of pure solvent, ${\mathrm{p}}_1^0$.
IDEAL SOLUTION

(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.

NON-IDEAL SOLUTION

When a solution does not obey Raoult’s law over the entire range of concentration, then it is called non-ideal solution.
In non-ideal solution the vapour pressure of such a solution is either higher or lower than that predicted by Raoult’s law, If it is higher, the solution exhibits positive deviation and if it is lower, it exhibits negative deviation.

IN case of non-ideal solution

Δ_mixH ,Δ_mixV
 both are not equal to zero. it either be less than zero or greater than zero.
 IN case of positive deviation it be larger and In case of negtive deviation it be lesser.
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 not nearly equal to those between A-B, this leads to the formation of non ideal solution.

example :a mixture of chloroform and acetone etc.