There are basically 4 definitions of oxidation and reduction:
OXIDATION
1) Increase in oxidation states
Eg: Fe 2+ ---> Fe 3+
An increase of oxidation staes from 2+ to 3+ ( obvious, isn't it? )
2) Gain of oxygen atoms
Eg: Pb + CuO --> PbO + Cu
In this case, Lead (Pb) has gain 1 oxygen atom to form lead(II) oxide (PbO)
3) Lost of hydrogen atoms
Eg: 2 H2S (g) + SO2(g) ---> 2H2O(l) + 3S (s)
In this case, hydrogen sulphide (H2S) has lost 2 hydrogen atoms to form sulphur (S)
Note: do not be CONFUSED by the ratio: 2H2S.
We are interested in the formula, H2S instead!
4) Loss of electrons
Actually, if you look closely, the LOST of electrons is similar to the oxidation states!!!
Why Do I Say That?
Consider this example,
Fe 2+ ---> Fe 3+2+ means lost of 2 electrons and 3+ means lost of 3 electrons.In this case, we say that Fe 2+ is oxidised to Fe 3+.
Compare the oxidation states, isn't 2+ a gain of OXIDATION STATES to 3+ ??
Similarly,
REDUCTION
1) Decrease in oxidation states
Eg: Zn 2+ ---> Zn
From oxidation states of 2+ to 0 ( a decrease in oxidation states )
2) Loss of oxygen atoms
Eg: Pb + CuO ---> PbO + Cu
Copper (II) oxide has lost 1 oxygen atom to form Cu
3) Gain in hydrogen atoms
Eg: N2 + 3H2 ---> 2 NH3
Nitrogen (N2) has gain 2 hydrogen atoms to form ammonia (NH3)
4) Gain of electrons
Eg: Zn 2+ + 2 e- ---> Zn
Zinc ion has accepted 2 electrons to become Zinc ztom
or
Zinc ion has decrease in its oxidation state from 2+ to zero.
( the first rule about decrease in oxidation states )
