Question

The below are oxidation reactions. Explain why?

   Metal + oxygen -> Metal Oxide

Magnesium + Oxygen -> Magnesium
Oxide
Zinc + Oxygen -> Zinc Oxide

Answer 1

They are oxidation reactions ONLY WITH RESPECT to the metal....

Explanation:

Why? Because while the metal is oxidized, in that its oxidation number increases from `0` to `+II`, the oxidation number of dioxygen reduces from `0` to `-II`.... The point is that for every electron loss, every oxidation, there is a corresponding electron gain, a reduction...and dioxygen gas is one of the most potents oxidants...

And we can do this formally for the zinc.... Zinc is OXIDIZED to `Zn^(2+)`, i.e. electron loss....

`Zn(s) rarr Zn^(2+) + 2e^(-)`....charge and mass are balanced as is absolutely required....and dioxygen is reduced.....

`1/2O_2+2e^(-) rarr O^(2-)`

And we add the former to the latter so that we can eliminate the electrons.....

`Zn(s) +1/2O_2+2e^(-)rarr underbrace(Zn^(2+)+O^(2-))_"i.e. ZnO" + 2e^(-)`

...to give finally....

`Zn(s) +1/2O_2(g) rarr ZnO(s)`

Capisce?