Question

The vapour pressure of pure water at 25 °C is 18 mm Hg. When nonelectrolyte is dissolved. its vapour pressure becomes 17.32 mm Hg.
What is the relative lowering of vapour pressure of the solution ?

Answer 1

The vapor pressure of pure water at 25°C is 18 mm Hg. When nonelectrolyte is dissolved. its vapour pressure becomes 17.32 mm Hg.

We have to find the relative lowering of vapor pressure of the solution.

“relative lowering of vapor pressure is the ratio of change in pressure to the vapor pressure of pure water. ”

vapor pressure of pure water, P₀ = 18 mm Hg

vapor pressure of solution (after dissolving nonelectrolyte within solution) , P = 17.32 mm Hg

now,

relative lowering of vapor pressure = (P₀ - P)/P₀

= (18 - 17.32)/18

= 0.68/18

= 0.0378

Therefore the relative lowering of vapor pressure of the solution is 0.0378