in redox reactions some elements act as electron donors, ie,oxidised;others - as acceptors, ie,restored.
In typical cases, the interaction of oxidizing and reducing agents you can immediately identify that it is a redox reaction.For example, the interaction with the alkali metal or halogen acids, the processes of combustion in oxygen.
Consider the more complicated case of the example of the reaction of potassium permanganate with potassium sulfite in the presence of large amounts of alkali hydroxide.To ensure that the oxidation-reduction reaction, to determine the degree of oxidation of elements in the right and left side.The atoms of one element always accept or
give the same number of electrons.This reaction is oxygen, hydrogen and potassium.Other oxidation may be different, like manganese and sulfur.
Determine the degree of oxidation of manganese and sulfur in the left side of the equation.Take potassium permanganate: oxygen is always a degree of oxidation of the electron acceptor (-2).Four 8 attached oxygen atom electrons.Potassium - electron donor and its oxidation state (1).One potassium atom gives an electron.Then manganese must give: 8-1 = 7 electrons.
similarly determined that the degree of oxidation of sulfide sulfur in potassium (4).Three oxygen atoms take 6 electrons, and two potassium atoms give two electrons.
Now find the degree of oxidation of these elements in the right-hand side.The potassium permanganate K2MnO4 four oxygen atoms attached eight electrons, and two potassium atoms give two.Hence, reduced manganese oxidation with (7) to (6), i.e.recovered.
Sulfur potassium sulfate, by contrast, oxidized with (4) to (6).The molecule K2SO4 four oxygen atoms take eight electrons, and two potassium atoms give two.Hence, six electrons are taken away at the sulfur atom.
The oxidation of manganese and sulfur changed.And you can conclude that the redox reaction.