## Non-ideal solutions Chemistry Notes

Those solutions which do not obey Raoult’s law are called non-ideal solutions. So, for such type of solutions

There is considerable change in volume and heat on addition of both components in non-ideal solutions. Most of the solutions are non-ideal because these deviate less or more from ideal behaviour. So, for non-ideal solution,

Any component in complete composition range does not obey Raoult’s law. So,

∆V(mixing) ≠ 0
∆H(mixing) ≠ 0
Attraction forces in A – B ≠ Attraction forces in A – A or B – B Non ideal solutions are of two types:

• Non-ideal solutions with positive deviation
• Non ideal solutions with negative deviation

Non-Ideal Solution with Positive Deviation :

In such type of solution,

• pA > $$p_{\mathrm{A}}^{0}$$ xA ; pB > $$p_{\mathrm{B}}^{0}$$ xB
• ∆ V(mixing) = + ve
• ∆ H(mixing) = + ve (Endothermic)

→ Here, the vapour pressure of solution is more than vapour pressure determined by Raoult’s law. Here, solvent-solvent and solute-solute intermolecular forces of attractions are strong than solvent-solute intermolecular forces of attractions i.e., A – A and B – B attraction forces are strong than A – Battraction forces. This is the reason that the volume of solution increases.

→ The examples of some non-ideal solutions with positive deviation are given below:

• Ethanol + water
• Ether + Acetone
• Carbon disulphide + Acetone
• Carbon tetrachloride + Methanol
• Ethanol + Cyclohexane
• Carbon tetrachloride + toluene
• Carbon tetrachloride + Chloroform
• Methanol + Water
• Acetone + Ethanol

Non-Ideal Solution with Negative Deviation :

In such type of solution

• pA < $$p_{\mathrm{A}}^{0}$$ xA ; pB < $$p_{\mathrm{B}}^{0}$$ xB
• ∆ V(mixing) = – ve
• ∆ H(mixing) = – ve (Endothermic)

→ Here, the vapour pressure of solution is lesser than vapour pressure determined by Raoult’s law. Here, solvent-solvent or solute-solute intermolecular forces of attraction are relatively lesser than solute-solvent intermolecular forces of attraction. It is the reason that the volume of solution is less. Some examples of non-ideal solution with negetive deviation are given below

• Chloroform + Acetone
• Chloroform + Benzene
• Water + HCl
• Water + NO3
• Pyridine + Acetic acid
• Chloroform + Ether
• Acetone + Aniline
• Methanol + Acetic acid