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Derivation%of%the%equation%
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Using%the%7%equations%listed%above,%the%following%equations%can%be%deduced.%%
(Let%
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= !! !! ! /!"#$%'($)!
= !!! !! !! ! /!"#$%&'($)!
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+
Specia%on(Diagram(EDTA(
1.00%
0.90%
Frac%on(of(species(
0.80%
[EDTA4N]%
0.70%
[H6(EDTA)2+]%
0.60%
0.50%
[H5(EDTA)+]%
0.40%
[H4(EDTA)]%
0.30%
[H3(EDTA)N]%
0.20%
[H2(EDTA)2N]%
0.10%
[H(EDTA)3N]%
0.00%
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
11%
12%
13%
14%
pH(
%
Use!Excel!to!plot!the!speciation!diagrams!of!citric!acid!and!phosphoric!acid! respectively!based!on!the!derivation!above.! %
Specia%on(Diagram(Citric(Acid(
1%
0.9%
Frac%on(of(Species(
0.8%
0.7%
0.6%
[H3C6H5O7]%
0.5%
[H2C6H5O7%N]%
0.4%
[HC6H5O7%2N]%
0.3%
[C6H5O7%3N]%
0.2%
0.1%
0%
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
11%
12%
13%
14%
pH(
%
%
%
Specia%on(Diagram(Phosphric(Acid(
1%
0.9%
Frac%on(of(Species(
0.8%
0.7%
0.6%
[H3PO4]%
0.5%
[H2PO4%N]%
0.4%
[HPO4%2N]%
0.3%
[P04%3N]%
0.2%
0.1%
0%
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
11%
12%
13%
14%
pH(
%
%
3.2!
!
Figure%1:%Speciation%Diagram%Citric%Acid%
Figure%2:%Speciation%Diagram%Phosphoric%Acid%
(The shaded areas in the diagrams represent useful buffer ranges, which are determined by!!"# ± !)
%
!
!!
%
•
In the Speciation Diagram Citric Acid, it can be seen that citric acid has three pKa values, separated by less than two. Also, the shaded areas overlap each