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I have currently completed a titration curve for glycine-HCl (2omL @ 0.1M, therefore 2.0mmol) where I have the known pH at each interval of added NaOH (adding 4mL each interval of 1.0M then measure pH).

I understand that at an equivalence point in a titration curve there are equal amounts of acid and base in the solution, and from this point a half equivalence point can be found (which is the point of equal concentrations of acid, base, and conjugate base, where the pH for the pKa can be found). I have calculated that the first equivalence point should be when there is an addition of 2.0mmol of NaOH (I believe this is wrong), and therefore at 1.0mmol of NaOH there should be the pKa but my value is 1.29. Comparing this to literature this is incorrect as it should be at approximately at a pH of 2.3.

When viewing the data I collected graphically 2.3 is correct for the first pKa. What would be the problem in my understanding and calculation, because this method worked for potassium dihydrogen phosphate and correlates my collected data to literature?

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