Immunoglobulin G (IgG), formerly called gamma globulin, is a principal antibody in blood serum.

Question

A 0.669 g sample of immunoglobulin G is dissolved in water to make 0.156 L of solution, and the osmotic pressure of the solution at 25 ∘C is found to be 0.708 mbar. Calculate the molecular mass of immunoglobulin G.

Answer 1

π = iMRT

π = osmotic pressure = 0.708 mbar

i = van't Hoff factor = 1 for IgG

M = molarity = ?

R = gas constant = 0.0821 Latm/Kmol

T = temp in K = 25º + 273 = 298K

Since R has units of atm, we will convert 0.708 mbar to atm as follows:

π = 0.708 mbar x 1 bar / 10³ mbar x 1 atm/1.01 bar = 7.0x10^-4 atm

Solving for M we have..

M = π / (i)(R)(T) = (7.0x10^-4) / (1)(0.0821)(298)

M = 2.86x10^-5 mol/L

Moles = 2.86x10^-5 mol/L x 0.156 L = 4.46x10^-6 moles

molar mass = g/moles = 0.669 g / 4.46x10-6 moles = 1.5x10⁵ g/mol