Question

A solution was made by dissolving 5.60 mg of hemoglobin in water to give a final volume of 1.00 mL. The osmotic pressure of this solution was 2.14×10-3 atm at 25.0°C. Calculate the molar mass of hemoglobin, which is a molecular compound and a nonelectrolyte. Give your answer in g/mol.

Answer 1

Ans:

Osmotic preesure = $\Pi$ = M x R x T           .....(1)

M = Molarity of solute   R = gas constant T = temperature

M = number of moles x 1000 / volume ( in mL)   and number of moles = mass given / molar mass

T = 25.0^oC = 298 K

$\Pi$ = 2.14 x 10^-3 atm. = 2.14 x 10^-3 x (1.01 x 10⁵) Pa

Now putting all the values in (1) gives

2.14 x 10^-3 x (1.01 x 10⁵) Pa = M x 8.314 x 298

= ((5.60 x 10^-3 grams/MM) / 10^-6 m³) x 8.314 x 298                                     (here MM means Molar mass)

it gives MM = 64191 grams per mole