Question

In protein precipitation, two liters of 5mM buffer solution with pH 5.2 is needed in the isolation of albumin. Which among the buffer solutions is best fitted for the said purpose?justify your answer.
a. acetate buffer with pka=4.73?
b. tris-aminomethane with pka= 8.08?
c. phosphate buffer with pka=7.20?
calculate and measure the amounts( in grams if solid and in mL if liquid) of weak acid and conjugate base needed to be able to prepare the chosen buffer solution.

Answer 1

You want to use a substance with pKa = 5.2 +/- 1 so from 4.2 to 6.2 and the closer you get to 5.2 the better. Here is a summary of what you need to do. You want 2 L of 0.005 M= ? mols.
pH = pKa + log b/a. Plug in the numbers and solve for b/a That's equation 1.
Then equation 2 is
a + b = 0.005 M. Solve the two equations simultaneously to find a and b, and convert to grams acid and grams base. Post your work in detail if you get stuck.
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