When 4.03 g of a nonelectrolyte solute is dissolved in water to make 745 mL of solution at 27 °C, the solution exerts an osmotic pressure of 823 torr.

Question

What is the molar concentration of the solution?

How many moles of solute are in the solution?

What is the molar mass of the solute?

Answer 1

π = iMRT

π = osmotic pressure = 823 torr

i = van't Hoff factor = 1 for a non electrolyte

M = molarity = moles solute / liter solution = ?

R = gas constant = 62.36 LTorr/Kmol

T = temperature in Kelvin = 27 + 273 = 300K

Solving for M, we have

M = π / (i)(R)(T) = 823 / (1)(62.36)(300)

M = 0.04399 moles/liter (MOLAR CONCENTRATION)

Calculate moles of solute:

0.04399 moles/L x 0.745 L = 0.03277 moles (MOLES)

Calculate molar mass of solute:

molar mass = grams/moles = 4.03 g / 0.03277 moles

molar mass = 123 g / mol (MOLAR MASS)