For a dilute solution containing 2.5 ~g of a non-volatile non-electrolyte solute in 100 ~g of water, the elevation in boiling point at 1 atm pressure is 2^ C . Assuming concentration of solute is much lower than the concentration of solvent, the vapour pressure ( mm of Hg ) of the solution is (take K_ b =0.76 ~K ~kg ~mol ⁻¹ )

Step-by-step solution

From Raoult's law, p^ -p p^ = No. of moles of solute No. of moles of solvent + No. of moles of solute When the concentration of solute is much lower than the concentration of solvent, array l p^ -p p^ = No. of moles of solute No. of moles of solvent 760-p 760 = 2.5 / m 100 / 18 ...(i) array From elevation in boiling point, T_ b =K_ b m array l 2=0.76 m m= 2 0.76 ...(ii) array From(i) and (ii), p=724 ~mm