Unit – III C – 01
- The solutions which obey Raoult’s law over the entire range of concentration are known as ideal solutions.
- The ideal solutions have two 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. ΔmixH = 0 and ΔmixV = 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.
- 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.
- A perfectly ideal solution is rare but some solutions are nearly ideal in behaviour. Solution of n-hexane and n-heptane, bromoethane and chloroethane, benzene and toluene, chlorobenzene and bromobenzene etc. fall into this category. Most of the dilute solutions behave as ideal solutions.
- The process of separation of one liquid from another liquid (binary mixture) having different boiling points by distillation is called fractional distillation.
- The separation is possible when the vapour phase has a different composition from that boiling liquid mixture.
- Thus the components of ideal solution can be separated by fractional distllation.
Examples of ideal solutions:
a) All dilute solutions
b) benzene + toluene
c) n-hexane + n- heptane
d) clorobenzene + bromobenzene
e) ethyl bromide + ethyl iodide
f) n-butyl chloride + n-butyl bromide