Question

When hydrogen burns, what is oxygen's role?

Answer 1

Oxygen acts as the `"oxidant"`, the acceptor of electrons.

Explanation:

The above definition is a formalism, but it does help us to rationalize reactivity. Oxygen lies on the right of the Periodic Table; its high nuclear charge tends to accept electrons, i.e. becoming reduced, and oxidizing another species:

`H_2(g) + 1/2O_2(g) rarr H_2O(g)`

In the reaction above, the reactants are elemental, and have an oxidation state of `0`. In the products, hydrogen has a formal oxidation state of `+I`, and the oxygen has a formal oxidation state of `-II`. Because of its tendency to accept electrons, `O` commonly has a formal oxidation state of `-II` in its compounds. When we assign oxidation states, we remember that these are formalisms; nevertheless, they give us an idea of electron transfer in the reaction.