Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Nickel(II) forms a complex with the EDTA ion, which has a charge of and six donor atoms. The sodium salt has the formula . Find the coordination number of nickel, the charge on the complex ion, and the number of sodium ions in one formula unit.
The coordination number is the number of donor atoms bonded to the metal, not the number of ligands. The charge on a complex is , where is the oxidation state of the metal. A ligand with two or more donor atoms is chelating, and EDTA has six.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The coordination number. One EDTA ion with 6 donor atoms gives a coordination number of 6.
Step 2. The charge. .
Step 3. The sodium ions. The complex ion is , so two ions are needed.
Answer: the coordination number is 6, the charge is , and . The formula is .
Check. The whole compound is neutral: .
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