A solution was made by dissolving 5.15 mg of hemoglobin in water to give final volume of 1.00 mL. The osmotic pressure of this solution was 1.97 x 10^-3 atm at 25C. Calculate the molar mass of hemoglobin.
pi = iMRT
i = 1 since hemoglobin is nonelectrolyte and doesn't dissociate
T = 298 K
R = constant = .08206 L atm/mol K
1 mL => .00100 L
5.15 mg => .00515 g
I was told that the answer is supposed to be a big number like 64,000. I don't understand how that works. Can someone help me get the right answer?
@DrBob222
Nothing is easy without dedication and hard-work. Just because you are a doctor, does not make this easy
pi = MRT
Solve for M in mol/L.
Then M = mols/L. You know M and L, solve for mols.
Finally, mols = g/molar mass and rearrange to molar mass = g/mols. You know grams and you know mol, solve for molar mass. I get close to 64,000 too.
To calculate the molar mass of hemoglobin, we need to rearrange the osmotic pressure equation, pi = iMRT, to solve for the molar mass (M).
pi = iMRT
Rearranging the equation:
M = pi / iRT
Now we can substitute the given values into the equation:
pi = 1.97 x 10^-3 atm (given)
i = 1 (since hemoglobin is a nonelectrolyte and does not dissociate)
R = 0.08206 L atm/mol K (given)
T = 298 K (given)
M = (1.97 x 10^-3 atm) / (1 x 0.08206 L atm/mol K x 298 K)
M = 0.238 x 10^-3 mol/L
Now, we need to convert the given mass of hemoglobin to moles using its molar mass:
Mass of hemoglobin = 5.15 mg = 0.00515 g
To convert grams to moles, we divide by the molar mass of hemoglobin (M):
0.00515 g / M = 0.238 x 10^-3 mol/L
Solving for M:
M = 0.00515 g / (0.238 x 10^-3 mol/L)
M = 0.00515 g / (0.238 x 10^-3 mol/L)
M = 216.39 g/mol
Therefore, the molar mass of hemoglobin is approximately 216.39 g/mol, not a large number like 64,000.