Chemistry colligative prop

Question

To determine the molar mas of a protein (i= 1) called a “zinc finger," a chemist dissolves 4.52x10^-4 g of the

Protein in 10.40 mL of water at 19.20C. When the solution Is placed in a U-tube, the amount of pressure

Required to restore the volumes to equal levels is 9.201x10^-4 atm. What is the molarity of the solution and

what is the molar mass of the zinc finger protein?

Answer 1

This is based on the change in the osmotic pressure produced by the protein. The formula we will use is...

π = iMRT

π = osmotic pressure = 9.201x10^-4 atm

i = van't Hoff factor = 1

M = molarity = moles protein / L = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in Kelvin = 19.20ºC + 273.15 = 292.35K

Solving for M, we have ...

M = π / (i)(R)(T)

M = 9.20x10^-4 atm / (1)(0.0821 Latm/Kmol)(292.35K)

M = 3.833x10^-5 M = 3.833x10^-5 mols / L

Find moles of protein:

volume of solution = 10.40 mls x 1 L / 1000 mls = 0.01040 L

3.833x10^-5 mols / L x 0.01040 L = 3.986x10^-7 moles

Find molar mass of protein:

molar mass = grams / moles

molar mass = 4.52x10^-4 g / 3.986x10^-7 mols

molar mass = 1134 g / mole