What is the ratio of copper(II) ions to EDTA in a $\ce{[Cu(EDTA)]^{2-}}$ complex?

I know that EDTA forms up to 6 coordinate bonds with the central atom, but is that what they are asking for with "ratio"? According to this website, it seems that copper actually bonds with all 6 free electron pairs.

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    – M.A.R.
    Mar 16, 2015 at 18:01
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    $\begingroup$ They're asking for the ration of ions i.e. for each $Cu^{2+}$ ion, how many $EDTA^{6-}$ are there. $\endgroup$ Mar 16, 2015 at 18:04
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    $\begingroup$ So all that would be is 1:1, that's it? $\endgroup$
    – DK2AX
    Mar 16, 2015 at 18:05
  • $\begingroup$ Yes that's right. $\endgroup$ Mar 16, 2015 at 18:05
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    $\begingroup$ @BinaryGeek EDTA has a maximum of a -4 charge. It can never reach -6. $\endgroup$
    – LDC3
    Mar 17, 2015 at 1:23

1 Answer 1


The ratio of Cu to EDTA is the number of copper ions per EDTA ion. In this case there is one EDTA ion for every copper ion so the ratio is 1:1.

Copper bonds with six electron pairs on EDTA to form the complex shown below where the central metal species is copper(II):

enter image description here


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