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I used this table (http://microscopy.berkeley.edu/Resources/instruction/buffers.html) to make a citrate buffer system. The Pka value is 6.4, and I multiplied the solution by ten to make a larger batch. I used 137ml of citric acid and 363ml sodium citrate in distilled water to make a buffer system with pH of 5.6. Now I'm trying to work backwards to prove this was correct, and using the equation pH = pKa + log(A-/HA) I am getting 6.4 + log 0.0137/0.0363 = 5.97, when it should be 5.6. Anyone know what I'm doing wrong? Thanks!

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    $\begingroup$ Remember it is not A-/HA, but A^3-/HA^2-. So for pH=pKa3=6.4, the molar ratio citrate/citric_acid is 5:1. H3A + 5 A^3- -> 3 HA^2- + 3 A^3- $\endgroup$
    – Poutnik
    Commented Feb 18, 2020 at 17:27

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