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It seems to me rusting is an electrochemical process where oxygen, which has particularly high electronegativity, fills the role of cathode or is that an incorrect way to put it?

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  • $\begingroup$ The main problem you're having is that electrochemical processes don't have to have a cathode/anode. $\endgroup$ – JavaScriptCoder May 5 '18 at 21:42
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Rusting is a redox reaction. $\ce{4 Fe + 3 O2 -> 2 Fe2O3}$

Redox reactions mean one chemical is being reduced and one is being oxidized. Reduction = electron gain, oxidation = electron loss. The reason it is called oxidation is because oxygen is so good at reducing other chemicals (it wants electrons). How do you tell what gets electrons in a compound? Oxidation numbers.

Oxidation numbers signify how many electrons each atom has. -n means it has n more than neutral state, +n means it has n less than neutral state. In molecules which have only one element, oxidation state is 0. So Fe/O2 both have oxidation state 0. There are some rules on oxidation states in compounds which are complicated, basically usually group 1 is +1, group 2 is +2, O is -2, and group 17 is -1. In this case each O in the end is -2, and Fe is +3. So each Fe lost 3 electrons.

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