Question

Which of the following is true about metal EDTA complex? (if it is a 3d metal)
A.The ratio of the moles of metal and EDTA in complex is $1:6$
B.The ratio of the moles of metal and EDTA in complex is $6:1$
C.The ratio of the moles of metal and EDTA in complex is $1:1$
D.3d metal ion cannot bond with EDTA

Answer 1

EDTA is a polydentate ligand, more specifically it is a hexadentate ligand. The full form of EDTA is Ethylenediaminetetraacetic Acid. Being a hexadentate ligand means that it has the capacity of having 6 bonding sites on its structure.

Complete step by step answer:
The molecular structure of EDTA can be given as:

The six bonding sites on the EDTA molecule are at the 4 -OH functional groups and the 2 N atoms (on the lone pairs).
Coming back to the question, let us discuss metals with the valence electron in 3d orbital. The 3d orbital has a maximum capacity of 10 electrons. The metal ions or atoms in this group have the capability of forming a 6 – valent coordination complex. These 6 valent coordination complexes will then react with one EDTA molecule. To put it in simpler terms, we can say that each site on the EDTA molecule can bond with one 3d metal ion. Since there are 6 sites in total, it has the capacity for bonding with 6 metal ions. Hence the ratio of the moles of metal and EDTA in the complex is $6:6$ . Or to simplify this value, the ratio of the moles of metal and EDTA in the complex is $1:1$ .

Hence, Option C is the correct option.

Note:
After being bound by EDTA into a metal complex, metal ions remain in solution but exhibit diminished reactivity. EDTA is produced as several salts as well.