The following data were obtained from the titration of a 25.0 mL weak base with

Question

The following data were obtained from the titration of a 25.0 mL weak base with 0.1 M HCl. Calculate Ka for the conjugate acid of this weak base.

I made a titration curve and figured out the equivalence point is at (17.5,5.05). 17.5 is the volume and 5.05 is the pH. Now I am just having trouble finding ka. I know that I am titrating a base, so I first have to find pkb, then convert to pka and find ka, but I am not sure how. I have done something like this before but with titrating an acid but this is different.

Please help and show steps if possible! Thanks.

Volume of HCl pH 0 11.05 1 10.86 2 10.78 3 10.42 4 10.12 5 9.5 6 9.2 7 9.1 8 8.8 9 8.4 10 8.02 11 8.5 12 8.43 13 7.96 14 7.56 15 7.12 16 6.89 17 6.65 18 3.45 19 3.33 20 3.21 21 3.15 22 3.05 23 3.01 24 2.96 25 2.9

Explanation / Answer

pkb equal to pH of half equivalent point.

half euivalent point = 17.5 /2 = 8.75 HCl have added which is around 8.4

now 1 / pkb = pka = 0.119

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