11_Complex-Formation_Titrations-page5

# 11_Complex-Formation_Titrations-page5 - H5Y 1 H 3 YY4 H4Y...

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Unformatted text preview: H5Y+ 1 H 3 YY4- H4Y H6Y2+ HY3- H2Y2- Under normal conditions, the H6Y2+ and H5Y+ forms are not present at significant levels. The effect of the hydrogen ion can then be calculated using !Y. ! .5 [Y4-] !Y = [H Y] + [H Y-] + [H Y2-] + [HY3-] + [Y4-] 4 3 2 0 0 2 4 6 8 10 12 = 14 [ Y ] / [ Y’ ] We can proceed through a series of substitutions leading to an equation in terms of [H+]. [H+] [ H3Y-] [H4Y] [H+] [ H2Y2-] [H3Y-] 1 Similar expressions can be written for the other two equilibria log !Y [H+]4 [H+]3 [H+]2 [H+] + + + +1 K1K2K3K4 K2K3K4 K3K4 K4 We can then calculate !Y and plotted as a function of pH. While the actual formation constant for a metalEDTA complex is: 0 pH ~11.5 All in Y4+ form -9 -18 0 !Y = [MY4-] KMY = [M] [Y4-] A conditional constant can be calculated at any known, constant pH as: 7 pH 14 KMY !Y = KMY’= [MY4-] [M] [Y’] ...
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