Ideal Solution - Practice Questions & MCQ

The solutions which obey Raoult’s law for the entire range of composition are called Ideal solutions. 

In these solutions, the solute-solute and solvent-solvent interactions are almost similar to solute-solvent interactions (A-B = A-A or B-B interactions). Since the existing forces and the newly formed forces are almost identical, there is no enthalpy change in the mixing of these solutions i.e

There is no change in the volume during the mixing process i.e. For example if 1 litre solutions each of liquid A and B are mixed to form an ideal solution, then the solution obtained has a volume equal to 2 litres.

The entropy of mixing is positive as new interactions are introduced into the solution which increases the randomness of the system and hence The mixing process is spontaneous and hence

These solutions have vapor pressure as predicted by Raoult’s law.
   

For the solutions to follow the ideal solution at all ranges of concentrations and temperatures then the molecular size of the liquids should be nearly the same. 
For example:

• CH₃OH + C₂H₅OH: Both these liquids are polar and have nearly the same size. Thus, this solution is an ideal solution.
• C₂H₅Br₂ + C₂H₅Cl₂: Both these liquids are polar and have nearly the same size. Thus, this solution is an ideal solution.
• C₂H₅Cl + C₂H₅Br: Both these liquids are polar and have nearly the same size. Thus, this solution is an ideal solution.
• C₆H₆ + C₆H₅CH₃: Both these liquids are non-polar and have nearly the same size. Thus, this solution is an ideal solution.
• C₂H₅Cl + C₂H₅I: Both these liquids are polar but the size difference between the molecules is large. Thus, this solution is not an ideal solution.