Non-ideal solutions Chemistry Notes

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

Non-ideal solutions Chemistry Notes 1

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,

Non-ideal solutions Chemistry Notes 2

∆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)

Non-ideal solutions Chemistry Notes 3

→ 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 solutions Chemistry Notes

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)

Non-ideal solutions Chemistry Notes 4

→ 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

Chemistry Notes