3 ~g of urea is dissolved in 45 ~g of H ₂ O . The relative lowering in vapour pressure is

Step-by-step solution

Relative lowering of vapour pressure p^ -p_ s p^ = n₂ n₁+n₂ where p^ = vapour pressure of the pure solvent. p_ s = vapour pressure of the solution n₂= number of moles of the solute n₁= number of moles of the solvent n₂= w₂ M₂ = 3 60 = 1 20 =0.05n₁= w₁ M₁ = 45 18 =2.5 p^ -p_ s p^ = n₂ n₁+n₂ = 0.05 2.5+0.05 =0.02