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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-]
0 2 4 6 8 10 12 = 14 [ Y ] / [ Y’ ] We can proceed through a series of
substitutions leading to an equation in terms
[H+] [ H3Y-]
[H+] [ H2Y2-]
can be written
for the other two
equilibria log !Y [H+]4
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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- Fall '08