Oxidation Number

[Tamera Scott 1G]

Today Lavelle mentioned that the oxidation state of Fe in the formula [Fe(CN6)]4- is +2. How did we conclude to that?

[Cody Do 2F]

Hey Tamera!

We know that the entire compound [Fe(CN)6] has a overall charge of -4. We also know that CN has a charge of -1 (Simply from making the lewis diagram and counting all the charges, etc.). The compound [Fe(CN)6) has 6 CN molecules, thus giving it a charge of -6. Now we ask ourselves what value is needed to go from -6 to -4. This value is +2. Thus, the charge of Fe must be +2.

[AlyssaBei_1F]

How do we know [Fe(CN)6] has an overall charge of -4? Is it given?

[Cody Do 2F]

Yeah, the overall charge of -4 is given by the superscript placed after the end square bracket!

[Fe(CN)₆]^-4 would mean that the entire [Fe(CN)₆] compound has a overall charge of -4 and thus Fe would have an oxidation state of +2.

If it were [Fe(CN)₆]^-3 instead, then the entire [Fe(CN)₆] compound would have an overall charge of -3 and thus Fe would have an oxidation state of +3 (as there are six negative charges given by the 6 CN molecules and an overall charge of -3).

[Tamera Scott 1G]

How do you figure out that CN has a -1 charge? I tried drawing out the lewis structure but did not get that answer.