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A 500 ml buffer solution contains .2M Acetic acid and .3M sodium acetate. Find the pH of the buffer solution after adding 20 ml of 1M NaOH, what is the pH?
(pka = 4.74)

  • chemistry-science -

    a) pH = pKa + [(base)/(acid)] will get the pH at the beginning.

    b)HAc + OH^- ==> H2O + Ac^-
    initial:
    HAc = 500 x 0.2 M = 100 millimoles.
    OH^- = 0
    Ac^- = 500 x 0.3M = 150 millimoles.

    change:
    OH^- = 20 mL x 1 M = 20 millimoles added
    HAc = 100-20
    Ac^- = 150 + 20

    final:
    HAc = 80 millimoles
    Ac^- = 170 millimiles

    Convert millimoles to concn, substitute into the HH equation above and solve for pH.

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