Question

0.102 g of an unknown(non electrolyte) compound is dissolved in enough water to make 100. mL of a solution and has an osmotic pressure of 28.1 mmHg at 20C. Calculate the molar mass of the compound.

Answer 1

680 g/m is the molar mass for the unknown, non electrolyte, compound.

Step-by-step explanation:

Let's apply the formula for osmotic pressure

π = Molarity . R . T

T = T° absolute (in K)

R = Universal constant gases

π = Pressure

Molarity = mol/L

As units of R are L.atm/mol.K, we have to convert the mmHg to atm

760 mmHg is 1 atm

28.1 mmHg is (28.1 .1)/760 = 0.0369 atm

0.0369 atm = M . 0.082 L.atm/mol.K . 293K

(0.0369 atm / 0.082 mol.K/L.atm . 293K) = M

0.0015 mol/L = Molarity

This data means the mol of solute in 1L, but we have 100mL so

Molarity . volume = mol

0.0015 mol/L . 0.1L = 1.5x10⁻⁴ mole

The molar mass will be: 0.102g / 1.5x10⁻⁴ m = 680 g/m