Question

25. At 298 K, vapour pressure of water is 17.54 mm Hg and the
vapour pressure of solution of 108.24 g of compound in 1000
g of water at the same temperature is 17.354 mm Hg.
Calculate the molar mass of the solute.​

Answer 1

Explanation:

Molar solution means 1 mole of solute dissolved in 1 kg of the solvent pressure of solution = mole fraction of solvent X vapour of pure solvent

Moles of solvent = mass / molar mass

= 1000 g / 18 g/mol

= 55.55 moles

so, total moles = 55.5 + 1

= 56.1 moles

So mole fraction of water = no of moles of water / total no of moles of solution

= 55.5 / 56.5

= 0.98

So vapour pressure of solution = 0.98 * 17.54

= 17.38 mm of Hg