Question

What is the molar mass of a vitamin if when you dissolve 0.500 g of it in a 80.0 mL of solution, the osmotic pressure of the solution is 85.6 mmHg at 25°C? (1 atm = 760 mmHg exactly)

Answer 1

Osmotic Pressure = iMRT
where
osmotic pressure in atm
i = van 't Hoff factor of the solute
M = molar concentration in mol/L
R = universal gas constant = 0.08206 L·atm/mol·K
T = absolute temperature in K

i = 1 (as vitamins does not dissociate in water)

T = 25+273 = 298 K

Pressure = 85.6/760 = 0.112 atm

M = moles / volume ----- > moles = weight in gm / Molar mass

so applying the formula

0.112 = 1 * (0.500/MM)/0.080 L * 298

MM = 16629.45 gm

Answer. Hope this helps you