Oxidation and Reduction

Oxidation and Reduction

In the Past

Oxidation: was the addition of oxygen to a substance.
Reduction: was the removal of oxygen from a substance or, in some cases, the addition of hydrogen.


Nowadays oxidation and reduction are explained in terms of electron transfer.

Oxidation: is the loss of electrons from a substance.
Reduction: is the gain of electrons by a substance.

Oxidation Numbers

An oxidation number: is the charge that an atom has or appears to have when the
electrons are distributed according to certain rules.

1. The oxidation number of an uncombined element or a diatomic molecule is zero.
2. The oxidation number of an ion is the same as the charge on the ion.
3. The sum of the oxidation numbers in a compound must add to zero.
4. The sum of the oxidation numbers un a complex ion must add up to the charge on
the ion.
5. Oxygen always has an oxidation number of 􀀀2, except in peroxides and in OF2>
6. Hydrogen is always +1 except in metal hydrides.
7. Oxidation number of flourine is always 􀀀1 as it is the most electronegative element.
8. Halogens (group 7) are always 􀀀1 unless bonded to amore electronegative atom.
9. Carbon can have an oxidation number of zero in some compounds.
Oxidation: is an increase in oxidation number.
Reduction: is a decrease in oxidation number.

Redox reaction: 

is a reaction where oxidation and reduction occur simultaneously. (One
cannot happen without the other).

Oxidising agent: is a substance that oxidises something else while it itself is reduced.

Reducing agent: is a substance that reduces something else while it itself is oxidised.

Applications of oxidising agents:

1. Swimming pools { add chlorine to kill bacteria.
CL2 is the oxidisng agent. When it oxidises the germ it kills it.

2. Bleaches as oxidising agents. Household bleach contains sodium hypochlorite Na-
CLO. H2O2 is used to turn coloured hair pigments colourless.

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