Question

. In Trial 1 0.435grams of KHP were dissolved in 100 mL of water and titrated with 21.06mL of NaOH that was later determined to be 0.101M.

Calculate the [C8H4O42-]Eq Pt, [OH-]eq, kb, pOH and pH values for the solution at the Equivalence Point.

At the Equivalence Point the KHP has been completely converted into the phthalate ion (C8H4O42-) - use the volume of base at the End Point (when the solution just turns pink) to be equivalent to the volume of base at the Equivalence Point.

Answer 1

First calculate the concentration of the phthalate ion at the Equivalence Point, then use this concentration as the "starting" concentration in the following equilibrium:

C8H4O42- + H2O ←→ HC8H4O4- + OH-

Let "x" be the [OH-]eq and set up an equation where

kb = x2 / ([C8H4O42-] - x)

Of course you're only given the ka of KHP (3.89 x 10-6), but you know how to convert it to the kb.

Finally, from the [OH-]eq, you can find the pOH and the pH.

[C8H4O42-]Eq Pt - calculate this answer from the 0.435grams of KHP used initially

Answer 2

@aaronq

Answer 3

@Timo86m @Photon336