Chemistry

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The pH of a 0.10 M solution of a certain acid is 3.25 at 25°C. What is the pH of a 0.010 M solution of the same acid at the same temperature?

  • Chemistry -

    pH = -log(H^+)
    -3.25 = log(H^+)
    Solve for (H^+). I estimated 5E-4 but you need to be more accurate than that.
    ..........HA ==> H^+ + A^-
    I.........0.1.....0.....0
    C.........-x.....x.....x
    E......-0.1-x....x......x
    and you know x = 5E-4 from above (again that is an estimate)
    Ka = (H^+)(A^-)/(HA)
    Solve for Ka.

    Then .....HA ==> H^++ A^-
    I........0.01.....0....0
    C.........-x.....x......x
    E......0.01-x.....x.....x

    Substitute the E line into Ka expression along with Ka determined from the first part and solve for x = (H^+), then convert to pH.

  • Chemistry -

    Oh I see what I did wrong! I got the answer 3.75. Thanks for the help!

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