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 molecular mass of the solute?

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 molecular mass of the solute? (A) 23.4 g mol-1 (B) 41.35 g mol-1 (C) 10 g mol-1 (D) 20.8 g mol-1

Tardigrade Admin · Accepted Answer

Vapour pressure of pure water at boiling point

= 1 a t m = 1.013 ba r

Vapour pressure of solution

(p s) = 1.004 ba r

Let mass of solution

= 100 g

Mass of solute

= 2 g

Mass of solvent

= 100 - 2 = 98 g

\frac{p ^{\circ} - p _{s}}{p ^{\circ}} = \frac{n _{2}}{n _{1} + n _{2}}

= \frac{n _{2}}{n _{1}} = \frac{W _{2} / M _{2}}{W _{1} / M _{1}} (∵ n_{2} <<< n_{1})

\frac{1.013 - 1.004}{1.013} = \frac{2}{M _{2}} \times \frac{18}{98}

or

M_{2} = \frac{2 \times 18}{98} \times \frac{1.013}{0.009}

= 41.35 g m o l^{- 1}

Q. 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 molecular mass of the solute?

$23.4 g m o l^{- 1}$

$41.35 g m o l^{- 1}$

$10 g m o l^{- 1}$

$20.8 g m o l^{- 1}$

Q. 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 molecular mass of the solute?

23.4gmol−1

41.35gmol−1

10gmol−1

20.8gmol−1

Q. 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 molecular mass of the solute?

$23.4 g m o l^{- 1}$

$41.35 g m o l^{- 1}$

$10 g m o l^{- 1}$

$20.8 g m o l^{- 1}$