When a non volatile solute is dissolved in a solvent the relative lowering of vapor pressure is equal to?

Vapour pressure of pure water at 298 K is 23.8 mm. 50 g of urea (NH2CONH2) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.

Vapoure pressure of pure water (solvent) at 298 K, p0 = 23.8 mmVapour pressure of solution, p = ?Mass of solvent ,W = 850 gMass of solute,M = 50 g

Mol. mass of water (H2O), M = 18 g mol–1
Mol.mass of urea NH2 CO NH2
= 14 + 2 + 12 + 16 + 14 + 2


= 60 g mol–1
According to Raoult's law, p0-pp0=ωMWm

                     p=p0-w×Mm×W×p°

                   p=23.8-50×1860×850

                      =23.8-0.017=23.78


Hence, 23.78 mm Hg. Ans.

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