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Posted by on Sunday, January 29, 2012 at 6:19pm.

1. MES (2-(N-Morpholino)ethanesulfonic acid) is a common buffer used in biochemistry labs to stabilize proteins. The pKa for MES is 6.09.
a. What is the pH of 1 liter of a 200 mM MES aqueous solution? Clue: you will need to solve a quadratic equation. (2.5 points)
b. How much solid NaOH (in grams) needs to be added to the MES solution to make a buffer at pH 6.5? (1.5 points)

  • Biochemistry - , Sunday, January 29, 2012 at 8:20pm

    If we call MES just HS, then
    ...........HS ==> H^+ + S^-
    initial....0.2.....0....0
    change.....-x......x.....x
    equil......0.2-x...x.....x
    Substitute the equilibrium values into the Ka expression and solve for x, then convert to pH.

    For the second part,
    you know pH = pKa + log(base/acid)
    (base) = (OH) that must be added
    (acid) = 0.2-(OH)
    I would plug that into the HH equation, solve for base and convert that to grams. I shall be happy to critique your work if you post it.

  • Biochemistry - , Monday, January 30, 2012 at 2:34pm

    Thanks Doc!

  • Biochemistry - , Tuesday, January 29, 2013 at 8:37pm

    Part A...
    Solving for x we will get 4.028x10^-4
    Plugging it in into pH equation, we will get pH of 3.39

    Part B
    5.76g

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