Question

When acetone and chloroform are mixed together, which of the following observations is correct? 

${{\text{(C}}{{\text{H}}_{\text{3}}}{\text{)}}_{\text{2}}}{\text{C = O  +  CHC}}{{\text{l}}_{\text{3}}}$

A                            B

A) A-A and B-B interactions are stronger than A-B interactions 

B) A-A and B-B interactions are weaker than A-B interactions 

C) A-A and B-B interactions are equal

D) The liquids form separate layers and are immiscible

Answer 1

Hint: Raoult’s law: It states that partial pressure of each component in a mixture is equal to the product of vapour pressure of pure component with the mole fraction of that component.If vapour pressure of the solution is less than that of expected Raoult’s law then it is said to be a negative deviation from Raoult’s law. If vapour pressure of the solution is more than that of expected Raoult’s law then it is said to be a positive deviation from Raoult’s law.

Complete step by step answer:
Positive deviation: In this type of deviation the vapour pressure of solution is greater than that of expected vapour pressure from Raoult’s law. This deviation arises when force of attraction between same molecules i.e. A-A or B-B interactions are greater than A-B interactions. For example: mixture of benzene and methanol shows positive deviations, mixture of chloroform and ethanol also shows positive deviations from Raoult’s law.
Negative deviation: In this type of deviation the vapour pressure of solution is lesser than that of expected vapour pressure from Raoult’s law. This deviation arises when force of attraction between same molecules i.e. A-A or B-B interactions are smaller than A-B interactions. For example: mixture of chloroform and acetone shows negative deviations from Raoult’s law.
Here in the question we are given with the mixture of acetone and chloroform. It is an example of negative deviation from Raoult’s law. Because the force of interactions between chloroform-chloroform molecules and the force of interactions between acetone-acetone molecules are lesser than the interactions between acetone and chloroform molecules. Because acetone and chloroform molecules are bonded by hydrogen bonds.

Hence option B is correct.

Note:
Hydrogen bond: It is defined as the bond between the highly electronegative atoms such as nitrogen, oxygen and fluorine with the hydrogen, is known as hydrogen bonding. This bond is formed due to dipole-dipole attraction between molecules.