Chemistry

Terephthalic( C8H6O4) is a diprotic acid with pka's 3.51 and 4.82.
a. What is the pH of a 0.15M solution of this acid?
b. What is the concentration of C8H4O4-2 in a 0.15M solution f this acid?

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asked by Delilah
  1. Let's call terephthalic acid H2T to make it simpler to write. You will have (H^+) from both ka1 and ka2. Take them one at a time.
    ............H2T ==> H^+ HT^-
    I............0.15........0......0
    C............-x............x......x
    E,,,,,,,,0.15-x..........x......x

    Ka1 = (H^+)(HT^-)/(H2T)
    Plug in the E line, solve for x = (H^+) and convert to pH. I've estimated x = 0.007 M but that's just an estimate. You need to calculate it yourself and make sure you can use the assumption that x is about zero if you choose to go that route. Then for Ka2.
    ............HT^- ==> H^+ T^2-
    I...........0.007......0.007...0
    C...........-x.............x..........x
    E........0.007-x....0.007+x....x

    plug the E line into Ka2 expression and solve for x = H^+ from Ka2.
    Total H^+ = H from ka1 + H from ka2.

    For part B that is x from Ka2 calculation.

    Post your work if you get stuck.

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