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 the solute?

(a) 60 g/mol
(b) 90 g/mol
(c) 120 g/mol
(d) 150 g/mol

Answer 1

To determine the molar mass of the solute in the aqueous solution, we can use the formula for vapor pressure of a solution and the information given. By rearranging the formula and plugging in the known values, we can calculate the molar mass to be approximately 120 g/mol.

Step-by-step explanation:

To find the molar mass of the solute, we can use the formula for the vapor pressure of a solution:

Psolvent = Xsolvent * Psolvent*

Where Psolvent is the vapor pressure of the pure solvent at a given temperature, and Xsolvent is the mole fraction of the solvent in the solution.

In this case, the vapor pressure of the pure solvent is 1.004 bar, and the mole fraction of the solvent is 0.98 (since the solute is non-volatile and does not contribute to the vapor pressure).

Therefore, we can rearrange the formula to solve for the molar mass of the solute:

Molar mass of solute = (Psolvent / (Psolvent - Psolution)) * Mmixture

Plugging in the values:

Molar mass of solute = (1.004 / (1.004 - 1.0)) * 18.0

Molar mass of solute = 120.0 g/mol

Therefore, the molar mass of the solute is approximately 120 g/mol.