101. Give one example each of miscible liquid pairs showing positive and negative deviatins from Raoult’s law. Give one reason for such deviations.

Answer:
According to Raoult's law the partial vapour pressure of each volatile compound in any solution is directly proportional to its mole fraction

if the vapour pressure is higher then solution is said to exhibit positive deviation
Positive deviation is shown by ethanol and water, cyclohexane and ethanol, acetone and diethylether etc.
Reasons:
(i) A—B interaction is weaker than A—A or B—B in positive deviation.

If the vapour pressure is lower then solution then solution is said to exhibit negtive deviation.
Negative deviation is shown by chloroform and acetone, methanol and acetic acid, H₂O and HCl, H₂O and HNO₃ etc.
Reason:
(ii) A—B interaction is stronger than A—A or B—B in negative deviation.