Biochemistry

How would you prepare 250ml of 0.2M sodium phosphate buffer of PH 6.4 if the following chemicals are available :dibasic sodium phosphate,monobasic sodium phosphate and 0.129M solution of NaOH. Assume that the pka1 pka2 pka3 of phosphoric acid are 2.12, 6.8 and 12.3 respectively. Molecular weights of dibasic and monobasic sodium phosphate salts are 142 and 138 respectively. Please this is an urgent question

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  1. Use Henderson-Hasselbalch equation and solve for (base)/(acid) ratio. That is equation 1. Use pKa2. Then set up
    (base) + (acid) = 0.2 for equation 2. Solve those simultaneously for (acid) and (base)
    Convert (acid) to grams NaH2PO4
    Convert (base) to grams Na2HPO4.
    Remember this will be grams in 250 mL.
    NOTE: The molecular weights are not right. Better check those again.

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