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preparation of a buffer

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Chefty:
hi all, these kind of problems kill me and i know ill see one on a test. i've been trying to work out this practice one but no luck

The following materials are available in pure form. A pH meter is not avail.
                  acetic acid  MW = 60  pKa = 4.76
                  TRIS         MW = 121 pKa = 8.00  tris-(hydroxymethyl)aminomethane
                  KH2PO4     MW = 136 pka for phos = 2.14,7.20,12.48
                  glycine*HCl MW = 111.5 pka = 2,34,9.60
                 histidine*HCl  MW = 191.7  pka = 1.82, 6.00, 9.17
                 aspartic acid  MW 133.5  pka = 1.88, 3.65, 9.60

                  1.0 Molar HCL
                  1.0 Molar NaOH

Give directions for the preparation of 500mL of a buffer pH 3.6, 0.060M and explain wh you have chosen the buffer system you have described. It is not acceptable to make 1.0L and discard part of it!


can someone show me how i would go about doing, i think the best bet would be to use the 2nd dis. of aspartic acid because its pka is closest to the desired pH but i'm still stumped

hmm, tried again but no luck i know i'm gonna have to solve 2 equations at the same time because
 [buffer] = [undiss. wk. acid] + [conj. base]
and
pH = pKa + log [conj. base]/[undiss. wk acid]
but my numbers come out wrong and then it just screws me. AHHHH!!! i HATE BUFFERS!!!!! i think i'm just gonna take points off on a test if i see one. I have all these handouts on making them but then when i try a problem like this no luck

Borek:
Approach is OK, work on your math.

faust:
if H3Asp = aspartic acid, a buffer solution of pH 3.6 will be a mixture of H2As-/HAsp^2- in equal quantity! Just us NaOH for the neutralisation

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