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Worked example: Using oxidation numbers to identify oxidation and reduction

By assigning oxidation numbers to the atoms of each element in a redox equation, we can determine which element is oxidized and which element is reduced during the reaction. In this video, we'll use this method to identify the oxidized and reduced elements in the reaction that occurs between I⁻ and MnO₄⁻ in basic solution. Created by Sal Khan.

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• After seeing Saraive7's question here, I am confused as to why MnO2 is not called manganite. And similarly, why is it carbon dioxide instead of carbonite? Since at least carbonite seems to exist, I can see that it has a -2 charge compared to the 0 charge for carbon dioxide; but I'm not able to understand the consistency with the naming...could someone explain?
• The "-ite" and "-ate" suffixes are reserved for oxyanions, or anions where another element is bonded to oxygen. MnO2 wouldn't be considered an oxyanion because it isn't an anion, it's a neutral compound. So it's just an oxide of manganese, or a neutral a compound where an element is bonded to oxygen. Now we can't just call it manganese oxide since there are several manganese oxides so we have to specify that it is manganese dioxide (1 manganese and 2 oxygens). Or manganese (IV) oxide where we specify the oxidation number of manganese which allows us to work out the number of oxygens.

The same reason goes for CO2 being carbon dioxide instead of carbonite, CO2 isn't an oxygen anion because it's neutral. So CO2 would be carbon dioxide, a neutral carbon oxide compound, and CO2^(2-) would be carbonite since it's an oxyanion.

Hope that helps.
• So I suppose ionic charge has the priority in determining oxidation number? Iodine has an ionic charge of 1- but isn't a free element supposed to have an oxidation number of 0?
• Oxidation number on a molecule must total to charge on the molecule. So, I-, which has a charge of -1, must have an oxidation number of -1, since there are no other atoms in the "molecule".
(1 vote)
• I thought the oxidation number for peroxides were -1 for oxygen. why did Sal write -2?
• That isn’t a peroxide, it’s manganese dioxide
• What do I do if my redox reaction is 4O + 3Na5 + 3Mg?
(1 vote)
• Where's the rest of your equation? Are those products, are they reactants? We don't know. We need to at least what our reactants and products are if we want to balanced redox reactions.