Red blood cells have a concentration of hemoglobin (Mw ~ 68000) at 0.3 M. The os

Question

Red blood cells have a concentration of hemoglobin (Mw ~ 68000) at 0.3 M. The osmotic pressure a body temperature (37°C) is 0.83 MPa. Water can permeate the cells walls, but not hemoglobin.

a. Using only the second osmotic coefficient, determine the coefficient value (L/g), and determine the activity of water at the conditions given above.

b. Calculate the ideal solution osmotic pressure at the conditions given above.

c. Suppose we were to transfer red blood cells in a laboratory solution at 37°C (blood banks need to do this). We want the external glucose solution to match the red blood cell’s internal osmotic pressure to avoid swelling or shrinking of the cells. If glucose has an osmotic pressure of 2 MPa at 0.7 M and 37°C, what glucose concentration (g/L) would match the internal osmotic pressure to keep the blood cells stable? What is molality of the resulting glucose solution? Comparing molalities, what can you infer about the solution non-idealities of the glucose solution compared to the hemoglobin solution?

Explanation / Answer

a) we know that

P= RT ( c/ M + B2c^2 )

B= viral coeffeceint

P = osmotic pressure = 8.19 atm

T = 310 K

R = 0.0821

c = 0.3 M

M = 68000

8.19 = 0.0821 X 310 ( 0.3 / 68000 + B2 X 0.09)

0.321 = 4.41 X 10^-6 + B2 X 0.09

B2 = 3.26 L / g approx

b) Ideal solution osmotic pressure

P = nRT / V = RT x concentration = 0.0821 X 310 X 0.3 = 7.63 atm

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