Chemistry

A 100.0 mL sample of 0.20M HF is titrated with 0.10M KOH. Determine the pH of the solution after the addition of 100.0 mL of KOH. The Ka of HF is 3.5 x 10^-4

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  1. millimoles HF = mL x M = 100 mL x 0.2M = ??
    mmoles KOH = 100 mL x 0.1M = ??

    ................HF + KOH ==> KF + H2O
    initial........20....0.......0......0
    add..................10..............
    change........-10.....-10.....+10...-10
    equil.........10......0........10....10

    Equilibrium concns are as follows:
    M = mmoles/mL
    (HF) = 10/200 = ??
    (KF) = 10/200
    Plug into the Henderson-Hasselbalch equation and solve for pH.

    OR, you can do it another way after working a number of these problems by recognizing that we are exactly half-way to the equivalence point. At that point, pH = pKa.

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