Redox

Redox means that reduction and oxidation takes place.

Reduction is gain of electrons, Oxidation is loss of electrons.

Oxidation was used for reaction where oxygen was added. E.g.: Cu + 1/2O2 => CuO
The copper has been oxidised to gain oxygen to become coper oxide. (Oxygen is an oxydising agent.)
The reverse is reduction. This would be, in the example, the reaction that turns Copper Oxide back into Copper. CuO + H2 => Cu + H2O. Copper oxide has been reduced,as it has lost oxygen, and therefore, hydrogen, as it made it happen, is the reducing agent.

So : When oxygen is added, it's oxidation, and when oxygen is taken away it's reduction, meaning, when Hydrogen is added, it's reduction, and when Hydrogen is taken away, it's oxidation.

Redox always involves electron transfer, and we represent this with half equations.

Cu + 1/2O2 => CuO
Cu => Cu2+ + 2e-

1/2O2 + 2e- => O2-

Cu + 1/2O2 => (Cu2+ + O-)

CuO + Mg => MgO + Cu
Cu2+ + 2e- => Cu (it looses the oxygen,and is therefore, reduced = gain electrons)
Mg => Mg2+ + 2e- (It gains the oxygen, and is therefore, oxidised= loss electrons.)
Combine them : Cu2+ + Mg => Cu + Mg2+

Oxidisng agents always accept electrons.
Reducing agents always give away electrons.

Questions from book : 1) Ca + Br2 => (Ca2+ + 2Br-)
a) Bromine has gained electrons.
b) Calcium has lost electrons.
c) Calcium has been oxidised.
d) Bromine has been reduced.
e) Ca => Ca2+ + 2e-
Br2 + 2e- => 2Br-
Ca +Br2 => (Ca2+ + 2Br-)
f) The oxidising agent is Bromine, it takes electrons
g) The reducing agent is Calcium, as it gives away electrons.

Rawwwr. Thoughts?