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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!!"# ± !)
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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