Question

An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of solute?

Answer 1

Good Morning Student,

Concentration is given in percent so that take mass of the solution = 100 g

Mass of non-volatile solute = 2% = 2g mass of the solvent = (100 — 2) = 98 g

Molecular mass of solvent (water) = 18

We have to find molecular mass of solute,

The vapour pressure of pure boiling water = 1atm = 1.013 bar.

Change in vapour pressure  = (1.013 — 1.004)

= 0.009 bar

$p_1$ ° - $p_1$ / $p_1$ ° = w2 × m1 / w1 × m2

0.009 / 1.013 bar = 2g / m2 × 18 g $mol^{-1}$

m2 = 41.35 g $mol^{-1}$

Hence,
Molar mass of the solute is 41.35 g $mol^{-1}$

Let me know if you have doubts especially regarding Physics, Chemistry or Maths.

Answer 2

Hope this answer helps you mate! ^_^