CHAPTER 3 :  OXIDATION AND REDUCTION

 A redox reaction can be defined as a reaction that involves oxidation and reduction at the same time (simultaneously).Oxidation is the process of losing electrons or the decrease in the oxidation number.

 Reduction is the process of gaining electrons or the decrease in the oxidation number.An oxidising agent is the substance that oxidises another substance,while a reducing agent is a substance that reduces another substance.The electron transfer in a redox reaction can cause a change in the axidation number.

                                                    Table 12.1  Nomenclature of metal elements according to the IUPAC system

                Table 12.2  Nomenclature of non-metal element according to the IUPAC system

 Chlorine  water,bromine water,acidified potassium manganate(VII) dichromate(VI) solution, all act as oxidising agents to oxidise iron(II) ion to iron(III) ion.Magnesium,zinc, and aluminium can act as reducing agents to reduce iron(III) ion to ion (II) ion.

      Table 12.3  The different oxidation numbers of transition elements

 The displacement of metal from its salt solution is a redox reaction.The dsiplacement reaction of halogen from its halide solution by other halogens is a redox reaction.

                                   Table 12.4  Observations of redox reactions

 The corrosion of metal occurs when it loses electrons to form the iron(II) ion.The rusting process of iron requires water and oxygen (air).The electrochemical corrosion of metals is a process that occurs when two metals with different electropositivity come into contact with an electrolyte; the more electropositive metal will donate electrons (oxidation) and corrodes.

 The rusting of iron can be prevented by using a protective layer such as through painting of the iron material,and also by using a sacrifical metal. The reactivity series of metals  is a sequence showing the vigour of the reaction of metals with oxygen.

 The reactivity series of metals can be used to predict whether a metal can reduce another metal from its metal oxide.Carbon is located between aluminium and zinc in the reactivity series of metals.

 Hydrogen is located between zinc and iron in the reactivity series of metals.Carbon is usually used to extract metals such as tin and iron from their metal ores.In the simple voltaic cell, the transfer of electrons occurs from the reducing agent th the oxidising agent.

 The oxidising agent and reducing agent in a simple voltaic cell is separated by a porous pot or salt bridge.The porous pot or salt bridge allows the transfer pf ions to occur.

 The oxidatin process that occurs at the anode involves the loss of electrons.The reducation process that occurs at the cathode involves the gain of electrons.The energy conversion that occurs in a chemical cell is:

            Chemical energy ------>  electrical energy