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curry 1E wrote:Why is it colbalt (III)? What is the oxidation number of the metal?
Cobalt has an oxidation number of 3+ because we see that there is an overall charge of 2-, there are 5 CN- molecules and 5 OH2 molecules. Because CN has a charge of -1, there is a total -5 charge from them alone. OH2 has no charge so we can ignore it. We are left with Co and we need to find its oxidation number, so we can set everything equal to -2 which is the overall charge.
Co + 5(CN-) + 5(OH) = -2
Co + 5(-1) + 5(0) = -2
Co - 5 + 0 = -2
Co = 5 - 2
Co = +3
Therefore, cobalt has an oxidation number of 3+.
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