Question

2. A solution is made by dissolving 2.0 g of an organic compound in ethanol at 22 °C. The volume of the resulting solution is 3.2 L and the osmotic pressure of this solution at 22°C is 1.7*10 -2 atm. What is the molar mass of this compound?

Answer 1

we use Osmotic pressure formula P = i x M x R x T

where P = osmotic pressure = 1.7 x 10^ -2 atm = 0.017 atm

R = gas constant = 0.082 Latm/molK

i = vant toff factor = 1 for non electrolytes

T = 22 C = 22 + 273 = 295 K

we first find Molarity M

0.017 atm = 1 x M x 0.082 latm/molK x 295 K

M = 0.0007 mol / L

Now molarity = moles of solute / solution volume in L

0.0007 mol / L = moles of solute / 3.2 L

moles of solute = 0.00225

Moles of solute = mass of solute / Molar mass of solute

0.00225 mol = 2g / ( molar mass)

Molar mass = 889 g/mol