Oxidation and reduction are two types of chemical reactions that often work together. Oxidation and reduction reactions involve an exchange of electrons between reactants. For many students, the confusion occurs when attempting to identify which reactant was oxidized and which reactant was reduced. What is the difference between oxidation and reduction?
Oxidation occurs when a reactant loses electrons during the reaction. Reduction occurs when a reactant gains electrons during the reaction. This often occurs when metals are reacted with acid. Consider the reaction between zinc metal and hydrochloric acid.
Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
If this reaction where broken down to the ion level:
Zn(s) + 2 H+(aq) + 2 Cl-(aq) → Zn2+(aq) + 2 Cl-(aq) + 2 H2(g)
First, look at what happens to the zinc atoms. Initially, we have a neutral zinc atom. As the reaction progresses, the zinc atom loses two electrons to become a Zn2+ ion.
Zn(s) → Zn2+(aq) + 2 e-
The zinc was oxidized into Zn2+ ions. This reaction is an oxidation reaction.
The second part of this reaction involves the hydrogen ions. The hydrogen ions are gaining electrons and bonding together to form dihydrogen gas.
2 H+ + 2 e- → H2(g)
The hydrogen ions each gained an electron to form the neutrally charged hydrogen gas. The hydrogen ions are said to be reduced and the reaction is a reduction reaction. Since both processes are going on at the same time, the initial reaction is called an oxidation-reduction reaction. This type of reaction is also called a redox reaction (REDuction/OXidation).
You could just memorize oxidation: lose electrons-reduction: gain electrons, but there are other ways. There are two mnemonics to remember which reaction is oxidation and which reaction is reductions. The first one is OIL RIG:
Oxidation Involves Loss of electrons
Reduction Involves Gain of electrons.
The second is "LEO the lion says GER".
Lose Electrons in Oxidation
Gain Electrons in Reduction.
Oxidation and reduction reactions are common when working with acids and bases and other electrochemical processes. Use these two mnemonics to help keep in mind which process is the oxidation and which is the reduction reaction.
More About Oxidation and Reduction