organic chem

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. Use the Henderson-Hasselbach equation:
pH = pKa + log [A-]/[AH], where A- is the conjugate base and AH is the weak acid.

Calculate the pH of an acetate buffer in which the acetate concentration [CH3COO-] is 3.5 times greater than acetic acid [CH3COOH]. pKa = 4.74.

9. How would you prepare a 0.6 M acetate buffer with a pH = 4.0?

  • organic chem -

    pH = pKa + log(acetate)/(acetic acid)
    You want (acetate)*3.5 = (acetic acid) so I would let CH3COOH = x and CH3COO^- = 3x
    Substitute into the HH equation and solve for pH.

    b.
    Use the HH equation, substitute Pka and pH and solve for base/acid ratio.
    The second equation you need is
    acid + base = 0.6M
    Solve those simultaneously to obtain base and acid, then use those values to prepare the solution from CH3COOH and CH3COONa (Note: You can use CH3COOH and NaOH but that requires more math.) Do it the easy way by weighing out CH3COOH and CH3COONa.

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