Question

How do you define oxidation and reduction?

Answer 1

Well, you could have two variations that I can think of, and each variation can have two different wordings, I suppose...

One (general) definition and its variation is:

• When an element's oxidation state becomes more positive.
• When an element's oxidation state becomes less negative.

Example:

`"Fe"^(2+) -> "Fe"^(3+) + e^(-)`

Here, the half-reaction demonstrates the oxidation state of `"Fe"` becoming more positive by `+1`.

And the other (organic) definition and its variation (that I can think of) is:

• When a species gains an oxygen.
• When a species loses a hydrogen.

Example:

`"Mn"^(2+) + 2"H"_2"O" -> "MnO"_2 + 4"H"^(+) + 2e^(-)`

Here, `"Mn"` changes oxidation state from `+2` to `+4`, but does so by gaining two oxygens.

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You can imagine how to define reduction, the exact opposite of all of these.