Question

In three beakers labeled as (A),(B), and (C ), 100 mL of water, 100 mL of 1 M solution of glucose in water, and 100 mL of 0.5 M solution of glucose in water are taken respectively and kept at same temperature.

Which of the following statements is correct?

• A. Vapour pressure in all the three beakers is same
• B. Vapour pressure of beaker B is highest
• C. Vapour pressure of beaker C is highest
• D. Vapour pressure of beaker B is lower than that of C and vapour pressure of beaker C is lower than that of A .

Answer 1

Answer: (D)

Vapour pressure of beaker B is lower than that of C and vapour pressure of beaker C is lower than that of A .

Answer 2

The vapour pressure of beaker B is lower than that of the beaker c, the vapour pressure of c is lower than that of beaker A.

The concept that is applied is Raoult’s law. The vapour pressure is directly proportional to the mole fraction. Beaker A has a non volatile solute hence pressure will be the highest. Beaker B has 1 M of glucose. Due to glucose the vapour pressure will be lower than the pure water. Therefore, lower than beaker A. Beaker C has 0.5M solution, the concentration of glucose is lower than beaker B therefore the sequence will be A> C> B