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Posted by on Tuesday, December 6, 2011 at 10:34am.

Determine the pH (to two decimal places) of a solution prepared by adding 15.9 mL of 0.0551 M sodium hydrogen oxalate (NaHOOCCOO) to 0.488 g of sodium oxalate (Na2OOCCOO).
Hydrogen Oxalate pKb of 12.77
Oxalate pKb of 9.81

  • Chemistry - , Tuesday, December 6, 2011 at 7:14pm

    mmoles acid = 15.9 x 0.0551 = ?
    mmoles base = 0.488/molar mass Na2C2O4)

    pH = pKa2 + log(base)/(acid)
    You must convert pKb above (you want the HC2O4^- to pKa by pKa + pKb = pKw = 14.
    Also, I have not taken the volume into account and used ONLY millimoles. Since that is a ratio, mmoles/mmoles cancels out the units AND since concn is mmoles/mL and the mL is the same for acid and base, the volume (whatever it may be) always cancels, too.

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