Solutions Test - 7

Molality is the number of moles of the solute present per kg of the solvent. Since the mass of the substance does not change on heating, molality is independent of temperature. Hence, option 2 is correct.
The other options are incorrect.
Molarity is the number of moles of solute present in a unit volume of the solution.
Molarity changes with change in temperature because the volume of the solution increases slightly with the increase in temperature and hence, the molality decreases.
Mole fraction is independent of temperature.
The unit of molality is mole/kg.

The solutions which obey Raoult's Law at every range of concentration and at all temperatures are Ideal Solutions. Ideal solutions can be obtained by mixing two ideal components that are, solute and a solvent having similar molecular size and structure. The forces of attractions between the molecules before and after mixing are the same.

The vapour pressure lowering of a solvent is proportional to the mole fraction of the solute.
The colligative properties depend on the concentration of the non- volatile solute.

On mixing, chloroform and acetone form a non-ideal solution with negative deviation.
This is because the intermolecular forces of attraction after mixing are stronger than the forces of attraction between the molecules of the pure components. Hence, the volume slightly decreases on mixing.

Solution of ethyl alcohol and water will have a positive deviation from ideal behaviour.
This is because the interactive forces after mixing are less strong than the interactive forces before mixing.