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

Question

A 0.984 g sample of immunoglobulin G is dissolved in water to make 0.198 L of solution, and the osmotic pressure of the solution at 25C⁢ is found to be 0.821 mbar. Calculate the molecular mass of immunoglobulin G.

Answer 1

π = MRT

π = osmotic pressure = 0.821 mbar = 8.21x10^-4 bar

M = molarity = moles IgG / liter = ?

R = gas constant = 0.08314 Lbar/Kmol

T = temperature in Kelvin = 25º + 273 = 298K

Solve for M

M = π / RT = 8.21x10^-4 / (0.08314)(298)

M = 3.31x10^-5 mole/L

Since we have only 0.198 L, we can find the moles..

moles of IgG = 0.198 L x 3.31x10^-5 mole/L = 6.56x10^-6 moles

The molar mass is defined as g / mole, so the molar mass is calculated as follows:

g = 0.984 g

moles = 6.56x10^-6 moles

molar mass of IgG = 0.984 g / 6.56x10^-6 moles = 149,973 g/mole = 149,973 Daltons = 1.50x10⁵ Daltons