oxidation states

Hi all

I am getting confused with oxidation states of my compounds can someone help me with the oxidation states of the cobalt metal.

[Co(NH3)5Cl]CL2

[Co(NH3)4Cl2)]CL

[Co(acac)2]

[Co(NH3)CO3]NO3-

Also the overall charge of the complex.
Thank you

Work out the overall charge of the complex by comparing with the charge on the counter ions.

For example, in [Co(NH3)5Cl]CL2, we know that Cl has a -1 charge, and there are two of them, so to make the compound neutral the charge on the complex part must be 2+.

Now, to work out the oxidation state of the cobalt you need to think about the charge on each of the ligands and also the overall charge of the complex.

So we know the complex is [Co(NH3)5Cl]](2+). We know that NH3 is neutral and Cl is -1. So the contribution to the charge from the ligands is -1 overall. So to get the complex to have an overall +2 charge this means that the cobalt contributes +3, which is its oxidation state.

You can use this expression : metal ox state = Overall complex charge - combined charge contribution from ligands, or just reason it out as above.

FYI, acac and CO are neutral.

For [Co(NH3)5Cl]Cl2
oxidation state Cl = -1, NH3 = 0 therefore Co = 2+

overally charge I got is 2+

for [Co(NH3)4Cl2]Cl

oxidation states Cl = -2 NH3 = 0 therefore Co = 1+

overall charge = ?

for [Co(acac)2]
oxidation state acac= 0 or is it -2 as 2 oxgyens are coordinated to the cobalt, colbalt = 1+ or 3+

for Co(NH3)CO3
Oxidation state NH3 = 0 CO3 = Is it -2 since 2 oxygen is coordinated to the cobalt? Overall charge ??

You need to work out the overall charge on the complex part first.

In the second question: [Co(NH3)4Cl2]Cl

The complex is [Co(NH3)4Cl2] and the counter ion is Cl. Cl is -1 therefore the overall charge of the complex is +1, ie the formula is [Co(NH3)4Cl2]+.

Using this, then work out the charge on cobalt.

metal ox state = overall complex charge - ligand charge

Co ox state = +1 - (4 x NH3 + 2xCl) = +1 - (-2) = +3.

therefor Co oxidation is +3 and charge is +1 for [Co(NH3)4Cl2]Cl

so for [CO(NH3)5Cl] Co oxidation is =

[Co(NH3)5Cl2]Cl, Cl is -2 and counterion outside the bracket is -1
therefore oxidation of Co + (-2) = -1
Co= (2+1)
Co=+3

charge = +2

is the above correct?

Also what is the overall charge of acac? Is it -2 as two oxgyen is attatched to Co. acac2-?

And the oxidation state of CO3 where 2 oxygen binds to the Co metal. CO3?

thanks for your help

I think you confused the formula a bit there ... there are 2 chlorines outside the complex in your question, and only one inside.

If we were to follow this one through though: [Co(NH3)5Cl2]Cl, then the charge on the complex would be +1, because it has to neutralise the -1 Cl on the outside of it.

The ligands would be indeed have a -2 charge, so to get the overall charge to be +1 the cobalt does need to contribute +3.



Acac is this, which is a neutral ligand.

Pretty sure that CO3 is supposed to mean 3 lots of a Carbon Monoxide molecule, which is a neutral ligand.

So now try the last two!

acac is -1 and CO3 is -2!

I worked out [Co(acac)2] charge=0, Co oxidation = +2

[Co(NH3)CO3]NO3
Charge = +1
Oxidation Co = 3+

is that correct?

Ooooh yeah, acac anion is the ligand So yep, charge is 0, ox state is +2

And yeah, I didn't realise that was carbonate

Soo, charge is +1, and ox state is +3, yep yep

Hi its me again, I have a small question to ask

What is the oxidation state of Cr in

[Cr(H2NC2H4NH2)2](SO4)3

When H2NC2H4NH2 is 0 and SO4 is -2
Im just a bit confused as there is two Cr.

thank you

there isn't two Cr, there is two H2NC2H4NH2's

3 x (SO4(2-)) = -6 => Cr = +6

My mistake it was suppose to be [Cr(H2NC2H4NH2)]2(SO4)3

ahh okay - well it's just +6/2 = +3 then

Thanks

also what is oxidation state of [Cr(H2O)6]3+
as the H2O are neutral does that make the Cr = +3