NEED HELP FAST!!!!

Question

Immunoglobulin G (IgG), formerly called gamma globulin, is a principal antibody in blood serum. A  0.567 g  sample of immunoglobulin G is dissolved in water to make  0.116 L  of solution, and the osmotic pressure of the solution at  25 ∘C  is found to be  0.807 mbar.  Calculate the molecular mass of immunoglobulin G.

Answer 1

Hi Andrea!

Good question - for this we're going to use the osmotic pressure formula to solve for the molality, which can get us to the molar mass.

Remember, osmotic pressure, π = i*m*R*T, where i is the Van't Hoff factor, m is molality, R is the gas constant, and T is the temperature. For this problem, we'll use 1 as the Van't Hoff factor, as IgG won't dissociate in water. We'll solve for the unknown m, after first converting the pressure to atmospheres (just to make it easier).

0.8070 mbar * (1 atm / 1013.25 mbar) = 0.0007964 atm

So using the osmotic pressure equation...remember to use Kelvin!

0.0007964 atm = (1) * (m) * (0.8206 L*atm/mol*K) * (298)

m = 3.26*10^-5 molal

Remember, molality is moles per kg of solvent, so we need to convert 0.116L to kg, using the density at 25 Celsius, which is 0.997 g/mL.

Mass = 0.116L * (1000 mL / 1 L) * (0.997 g / 1 mL) * (1 kg / 1000 g) = 0.1157 kg

Molality = 3.26*10^-5 = x moles / .1157 kg solvent

x = 3.77*10^-6 moles

So to get our molar mass, we use the normal equation, of grams per mol...

MM = (0.567 g) / (3.77*10^-6)

MM = 150538 g/mol

Hope that helps!!

-Niral