Question

A solution of acetone is ethanol:
(A) Shows a negative deviation from Raoult’s law.
(B) Shows a positive deviation from Raoult’s law.
(C) Behaves like a non-ideal solution.
(D) Obeys Raoult’s law.

Answer 1

Acetone is nearly non-polar and ethane is highly polar. Positive derivation occurs when vapour pressure of the component is greater than expected value while negative deviation occurs when total vapour pressure is less than expected value.

Complete step-by-step answer: Molecules of ethanol in pure state are hydrogen bonded but when acetone is added to the ethanol, molecules get in between the molecules of ethanol and break some of the hydrogen bond, which weaken the intermolecular attractive forces resulting in increase in vapour pressure of mixture than ethanol is pure state.
Because of this, acetone-ethanol interaction is weaker than ethanol-ethanol interaction which exhibits hydrogen bonding.

Additional information: There are two type of deviation :-
Positive deviation :Roult's law is a law of physical chemistry with implications in thermodynamics. Liquids will show positive deviation when the total vapour pressure is greater than what it should be according to Roult's law or the solute-solvent forces of attraction are weaker than the solute-solute and solvent-solvent interaction.
Negative deviation : Liquids will show negative deviation when the total vapour pressure is less than what it should be according to Roult's law or the solute-solvent forces of attraction are greater than the solute-solute and solvent-solvent interaction.

Hence, the correct option is (B) shows a positive deviation form Raoult’s law.

Note: : Acetone and ethanol both the components escape easily showing higher vapour pressure than the expected value. Enthalpy of mixing is positive, $\vartriangle mixH > 0$ and volume of mixing is positive, $\vartriangle mixV > 0$