Question

a cylinder filled with a movable Piston contains liquid water in equilibrium water vapour at 25 degree Celsius which one of the following operations result in a decrease in equilibrium vapour pressure

Answer 1

Hmmm. Choices?
lower temperature?

Answer 2

Dissolve salt in water

Answer 3

Since the vapour pressure depends on surface area, therefore when the surface area is more,vapour pressure will be more. When we add solute,what we do is we decrease the vapour pressure of solvent because some of the salt ions will be present at the solvent surface,thus taking place of some of the solvent particles which were actively participating in maintaing that previous high value of vapour pressure.so the equlibrium vapour pressure value decreases.