When 3.87 g of a nonelectrolyte solute is dissolved in water to make 235 mL of solution at 28 °C, the solution exerts an osmotic pressure of 857 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 = 857 torr x 1 atm/760 torr = 1.13 atm

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

M = molarity = moles solute/liter solution =?

R = gas constant = 0.0821 L-atm/K-mol

T = temperature in K = 28 + 273 = 301K

Solving for M we have...

M = π / (i)(R)(T) = 1.13 atm / (1)(0.0821)(301)

(a) M = 0.0457 mol/L = 0.0457 M

(b) moles = 0.0457 mol/L x 0.235 L = 0.0107 moles

(c) molar mass = 3.87 g / 0.0107 moles = 362 g/mol