|
oxidation-reduction reactions
When we take an iron metal nail and dip it into a
blue solution of copper (II) sulfate, the nail becomes covered with
a reddish substance. This reddish susbtance is metallic copper. The
equation for this is:
| Fe(s) +
CuSO4(aq) -> FeSO4(aq) + Cu(s) |
|
The net ionic equation, that is, the equation in
which we have cancelled out the spectator ions (in this case the
spectator ion is SO4) is:
| Fe0(s) +
Cu2+(aq) -> Fe2+(aq) +
Cu0(s) |
|
What we have done here is to show you the oxidation numbers above
the elements in the equation. This shows that the iron metal loses
electrons to form iron(II) ions while copper(II) ions gain
electrons to create copper metal. The Cu2+ on the
reactants side of the equation has a 2+ because SO4 has
a charge of 2-. Any reaction like this that involves a transfer of
electrons is an oxidation-reduction reaction.
We can write the equation above in the form of two half-reactions.
A half-reaction is one of two parts of an oxidation-reduction
reaction, one of which involves a loss of electrons, and the other
a gain of electrons. The half reactions for the iron nail reaction
would be:
1. Fe(s) ->
Fe+2(aq) + 2e-
2. Cu+2(aq) + 2e- -> Cu(s) |
|
The first equation shows us that electrons are lost by Fe,
(2e-). The second equation shows electrons being gained
by Cu2+. You know, we can also express this reaction in
terms of what happened to the oxidation number. The oxidation
number of iron increases after the reaction, while the oxidation
number of copper decreases.
Basically, an oxidation-reduction reaction (redox reaction) is a
reaction in which electrons are transferred between species or in
which atoms change oxidation numbers. Oxidation is the portion of
the redox reaction in which there is a loss of electrons by a
species or an increase in the oxidation number of an atom.
Reduction is the part of a reaction in which there is a gain of
electrons by a species or a decrease in the oxidation number of an
atom. Something that is oxidized loses electrons or contains an
atom that increases in oxidation number. Something that is reduced
gains electrons or has an atom that decreases in oxidation number.
An oxidizing agent is a something that oxidizes something, meaning
that the oxidation agent is itself reduced. A reducing agent is a
something that reduces something else, and is itself oxidized.
Notice the example below.
Fe is oxidized and Fe is the reducing agent. Cu+2 is
reduced and Cu+2 is the oxidizing agent. |