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A, EDTA dissociation balance
In the solution, 2 carboxyl H + transferred, amino N bipolar ion:
H4Y commonly, EDTA due to its solubility in water and acid is used as the second, sodium Na2H2Y: 2H2O, nicknamed EDTA, too.
When the solution of high acidity, two carboxylic can then accept H + +, equivalent to H6Y2, forming a six-member acid, six dissociation constants:
Ka1 = 10-10-160 Ka2 = 0.9 Ka3 = 10-2.1
Ka4 = 10-280 Ka5 = 10-10 - Ka6 = 24% of 6.2
Seven:
H6Y2 +, H5Y +, H4Y, H3Y - and H2Y2 - and HY3 - and Y4 -
When the pH < 1, mainly H6Y2 + form,
When the pH > 11, mainly Y4 - form - coordination ion.
Second, M - EDTA characteristics
1, EDTA wide coordination, almost all the metal ions to form stable chelates
Benefit: offers a wide range of possibilities were superior to acid and alkali, precipitation) (
Disadvantages: multiple components to interference between — selectively
2 and EDTA and formation of M - EDTA coordination than most for 1-1
3, chelated most charge, soluble in water, fast reaction.
CAS aubject 6381-92-6