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Titration of 25mL of a 0.05M Zn2+ sln with 0.055M EDTA in a sln buffered at pH 8. What's the conditional formation constant for Zn at pH 8?

Assume that the temperature is 25C and that the formation constant for Zn2+ is 3.13 x 10^16 at this temperature.

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  • 2 months ago

    [alphaY4-] at pH 8 = 5.4 x 10^-2

    Kf = 3.13 x 10^16

    Kf' = [alpha[Y4-].Kf = 1.69 x 10^15

    (a) mmol of Zn2+ before titration = 0.05 M x 25 ml = 1.25 mmol

    (b) Volume of EDTA required to reach equivalence point = 1.25 mmol/0.055 M = 23 ml

    (c) Kf' at equivalence point = 1.69 x 10^15

    (d) pZn before titration begin = -log(0.025) = 1.60

    let x amount has gone under change

    Kf' = 1.69 x 10^15 = 0.025/x^2

    x = 3.85 x 10^-9 M

    pZn = -log(3.85 x 10^9) = 8.41

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