When 4.31 g of a nonelectrolyte solute is dissolved in water to make 345 mL of solution at 25 °C, the solution exerts an osmotic pressure of 851 torr.

a. What is the molar concentration of the solution?

b. How many moles of solute are in the solution? c. What is the molar mass of the solute?

a) 0.046 mol/L

b) 0.016 mol

c) 271.58 g/mol

Explanation:

A nonelectrolyte solute is a solute that, when dissolved in a solvent, will not make the solution a conductor, and so the electricity will not pass through it. The osmotic pressure is a colligative property, and it's the pressure difference needed to stop the flow of a solution across a semipermeable membrane. It can be calculated by:

π = MRT

Where π is the osmotic pressure, M is the molarity of the solute (mol/L), R is the ideal gas constant, and T is the temperature (in K). For a pressure in torr, R = 62.3637 torr. L / (mol. K).

a) π = MRT, T = 25°C = 298 K

851 = M*62.3637*298

18584.3826M = 851

M = 0.046 mol/L

b) The number of moles of the solute (n) is the molar concentration (molarity) multiplied by the volume. So, for a solution of 345 mL = 0.345 L,

n = 0.046 * 0.345

n = 0.016 mol

c) The molar mass (MM) is the mass divided by the number of moles:

MM = 4.31/0.016

MM = 271.58 g/mol