Question

How do you work out the oxidation number of an element in a compound? E.g finding the oxidation number of the element Cr from the compound `Cr2O3`

Answer 1

The overall compound has a no charge (neutral). That means the positive and negative charges are equal in number. For the compound `Cr_2 O_3`, Chromium is a metal and hence its oxidation number is positive, lets say +x is its oxidation number. The oxidation number of oxygen is already known i.e -2. So, we can write an equation, as

`2* (+x) + 3* (-2) = 0`
(We equate it to zero because he overall charge is 0)

or 2`x-6 = 0`

or `2x= +6`

or `x = +3`