Question

Consider the following case in Ostwald-Walker Method:
Dry air is passed through a solution and then the dehydrating agent. Then, the Loss of weight of solution container will be propotional to :

• A. Vapour pressure of the solution.
• B. Mass of dehydrating agent taken.
• C. Nature of dehydrating agent taken
• D. Molal elevation constant

Answer 1

The correct option is A Vapour pressure of the solution.

Dry air is passed through a solution and then the dehydrating agent.

The dry air will absorb the vapours when it is passed through the solution.
More the vapour pressure of solution, more will be the vapours formed.
After the vapours are absorbed, the solution tries to re-establish the equilibrium , and the loss in mass of the solution will be proportional to the vapours absorbed by the dry air, which in turn is proportional to the vapour pressure of solution.
So, option (a) is correct.
Also, gain in weight of dehydrating agent is proportional to vapour pressure of the solution, since dry air absorbs vapours proportional to the vapour pressure of solution.