Here's a simple video before i the explanation. enjoy :)



This is very hard and difficult to understand explanation on oxidation from wikipedia (the link is at the end), if you can understand(i don't), then you're a genius! If not, read the simplified version of oxidation by scrolling down.

''Oxidation state is the measure of the degree of oxidation of an atom in a substance. It is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules: (1) the oxidation state of a free element (uncombined element) is zero; (2) for a simple (monoatomic) ion, the oxidation state is equal to the net charge on the ion; (3) hydrogen has an oxidation state of 1 and oxygen has an oxidation state of -2 when they are present in most compounds. (Exceptions to this are that hydrogen has an oxidation state of -1 in hydrides of active metals, e.g. LiH, and oxygen has an oxidation state of -1 in peroxides, e.g. H2O2; (4) the algebraic sum of oxidation states of all atoms in a neutral molecule must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion. For example, the oxidation states of sulfur in H2S, S8(elementary sulfur), SO2, SO3, and H2SO4 are, respectively: -2, 0, +4, +6 and +6. The higher the oxidation state of a given atom, the greater is its degree of oxidation; the lower the oxidation state, the greater is its degree of reduction.''

As taken from: http://en.wikipedia.org/wiki/Oxidation_state



In simple terms, oxidation is an increase in the oxidation number. Before we go on, oxidation is the interaction between oxygen molecules and the different kind of other substances there is they may contact, the substabces ranging from metal, plastics, living tissue.

Reduction is the decrease in oxidation numnber.An increase in oxidation number means that the oxidation number is getting more positive (+), therefore less minus. Oxidation is the loss of electrons, which are (-). A decrease in oxidation number means that the oxidation number is getting less plus, therefore more minus. Reduction is the gain of (-) electrons.

Therefore, higher oxidation number = positive (+) atom/molecule
lower oxidation number =negative (-) atom/molecule

Oxidation causes many things to happen, a common example being the rusting of metals:



Also, oxidation causes fruits to turn brown.
From that very moment when fruits are cut or bruised, the oxygen has free access to the plant tissue. In the presence of oxygen, polyphenol oxidase (PPO) enzymes in the chloroplasts rapidly oxidize phenolic chemicals naturally encountered in the fruit tissues to o-quinones. These chemicals interact with amino acids from proteins or they self-assemble to form brown polymers.



In conclusion, oxidation occurs when oygen reaches contact with enzynmes in the fruit and this causes chloroplasts to oxidize chemicals which are found in the fruit's tissues to form a substance which interacts woth amino acids or they self assemble to form browm polymers.

But this reaction is not the same in all fruits, since PPO activity and the amount of the phenolic chemicals can vary between different fruit varieties. PPO presence can also present variations linked to growing conditions and fruit maturity.

Browning can be impeded by either decreasing PPO oxidation activity or the quantity of phenols. Coating freshly cut apples in sugar or syrup can decrease oxygen diffusion, speeding down the reaction. Lemon or pineapple juices, rich in antioxidants, slow enzymatic browning when the apple is peeled. The acidity of these fruits also inhibits PPO activity.




However, the browning process is not always a bad thing. Wonder why tea, coffee and cocoa are brown? Indeed, browning is the cause of it all and browning which we know, is linked to oxidation.

Anyone fancy a drink?