What is ideal and non ideal solution?

Aug 26, 2022, 16:45 IST

IDEAL SOLUTION 

Ideal solution obeys Raoult’s law for binary mixture of component A and B present in mixture with mole fraction XA and XB. If both components are volatile in nature then partial pressure of each component PA and PB should be less than [Pure component vapour pressure of A] and 

But, 

So,

If a graph is plotted between vapour pressure and composition for ideal solution PA, PB, Ptotal are represented by straight lines.

So, it can be stated in another way that ideal solution is that solution which obey Raoult’s law for any concentration.

This type of ideality is impossible in actual practice. This is why solutions with very dilute [< 0.2 M] assumed to behave ideally.

For ideal solution each component must have symmetry both in size and nature (molecular attraction with each other otherwise they do not behave ideally.

So for ideal solution, 

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Some examples of solution that is nearest to ideality.

(i) Benzene + Toluene

(ii) Hexane + Heptane

(iii) Ethyl bromide + Ethyl iodide

(iv) Chlorobenzene + Bromobenzene

NON IDEAL SOLUTION

Due to dissymmetry in the size and nature of different component, they do not obey Raoult’s law. There are two type of non ideal solution of liquid components exists.

(a) Non ideal solution with positive deviation: They are characterised by 

Ptotal > PA + PB

This type of deviation occurs in components in which molar attraction is negligible with large size and shape difference.

They form minimum boiling azeotropic solution at a given composition.

Examples of non ideal solutions with positive deviation

(i) Acetone + Carbon disulphide

(ii) Acetone + Ethyl alcohol

(iii) Benzene + Acetone

(iv) Water + Methyl alcohol

(v) Ethyl alcohol + Water

(vi) Carbon tetrachloride + Chloroform

(vi) Carbon tetrachloride + Benzene

(vii) Carbon tetrachloride + Toluene

The boiling point of such composition mixture is lower than pure component boiling point of A and B respectively.

Azeotropic mixture can not be separated by simple distillation method because the composition of both vapour and liquid phase is same for both component and the boiling point remains constant till all the rest mixture evaporate so they can not be separated and they are also known as constant boiling mixture.

(b) Non–ideal solution with negative deviation

When the amount of molecular attraction between components A and B is valid and favoured by shape and size of them at proper composition. These are characterised by

and

Such mixture form maximum boiling point azeotropic at definite composition.

Examples of non ideal solutions with negative deviation

(i) Chloroform + Benzene

(ii) Chloroform + Acetone

(iii) Chloroform + Diethyl ether

(iv) Acetone + Aniline

(v) HCl + H₂O

(vi) HNO₃ + H₂O

(vii) CH₃COOH + Pyridine

What is ideal and non ideal solution? pdf