Oxidation

[Mariah Tumbaga 1e]

how do we figure out what an oxidation number is when given a formula?

[Krish Seth 2L]

Oxygen usually has an oxidation number of -2, and hydrogen has an oxidation number of +1. The total oxidation numbers of the molecule should add up to 0. For example, if you are given H3PO4, the oxidation number of P would be +5, as the hydrogens add up to +3, and 4 oxygens add up to -8.

[Sean Choi 4K]

For oxidation numbers, some elements have set oxidation numbers. It is a matter of just knowing them and remembering them. To add on to the other reply, h3po4, h is usually +1 but can take -1. Oxygen is usually -2. Since phosphoric acid is neutral, and there are three hydrogens meaning a 3+ oxidation number along with the 8- from the oxygen, phosphorus must have oxidation number 5.