How many EDTA (ethylenediaminetetraacetic acid) molecules are required to make an octahedral complex with a Ca2+ ion?
(a) Six 

(b) Three

(c) One

(d) Two.

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1 Answers

(c) : EDTA, which has four donor oxygen atoms and two donor nitrogen atoms in each molecule forms complex with Ca2+ ion. The free acid H4 EDTA is insoluble and the disodium salt Na2H2 EDTA is the most used reagent.
Ca2+ + [H2EDTA]2– → [Ca(EDTA)]2– + 2H+

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