Oxidation and Reduction

Reactions involving the transfer of electrons are known as oxidation - reduction (or redox) reactions.

Everyday examples inlclude Rusting The browning of apples Respiration Photosynthesis In the rusting of iron, iron reacts with oxygen and water, forming first Fe2+ ions and eventually Fe3+ ions. In this reaction the iron atoms lose electrons and are oxidised. Oxygen atoms gain electrons and are reduced.

Oxidation is the loss of electrons. Reduction is the gain of electrons. OIL RIG

*Metals are usually oxidised in a reaction, since they form positive ions and therefore lose electrons. Non-metals, on bonding with metals, usually form negative ions, and are therefore reduced*

An oxidising agent is a substance that allows oxidation to happen by gaining electrons itself.e.g. Oxygen - combustion, respiration      Hydrogen Peroxide - stain removal, bleaching of hair

A reducing agent is a substance that allows reduction to happen by losing electrons itself.e.g. Sulfur Dioxide - Bleaching agent      Carbon Monoxide - Production of metals from ore.

The electrochemical series:When metals react chemically, their atoms tend to be oxidised, forming positive ions. Some metal atoms, such as the atoms of alkali metals, have a greater tendency to lose electrons than others, such as transition metal atoms. Therefore, alkali metal atoms are more reactive. In the electrochemical series the metals are arranged in order of tendency to be oxidised.Potassium (Poor)Calcium (Concentration)Sodium (Soon)Magnesium (Means)Aluminium (A)Zinc (Zero)Iron (In)Tin (The)Hydrogen (Higher)Lead (Leaving)Copper (Cert)A metal will displace a less reactive metal from a solution of its salt. The more reactive metal is oxidised and the less reactive metal is reduced. e.g. reaction of zinc with acidified copper sulfate and magnesium with copper sulfate.An application of this type of reaction is the use of a less valuable metal, such as scrap iron, to displace a more valuable and less reactive metal, such as copper from a solution of its salts.

An electrolyte is a substance that conducts eletricity when dissolved in water or when molten. e.g. Acids such as hydrochloric acid and sodium hydroxide, and salts such as sodium chloride.Electrolysis is the breaking up of a substance due to the passage of an electric current through it in aqueous solution or when molten.In electrolysis, electrodes, which are conductors connected to the positive or negative terminals of a d.c. power supply, are dipped into an electrolyte in aqueous solution or in the molten state. + ions (cations) are attracted to the - electrode (cathode), where they receive electrons and are reduced. - ions (anions) are attracted to the + electrode (anode), where they lose electrons and are oxidised.OXIDATION OCCURS AT THE ANODE, AND REDUCTION OCCURS AT THE CATHODE.

ELECTROPLATINGa layer of metal is put onto the surface of another metal.e.g. cutlery made of nickel can be coated with silver increasing its value and improving its appearance. The cutlery is stamped with the letters EPNS (electro-plated nickel silver).Another example of electroplating is the coating of steel with chromium to imprvoe its a ppearnace and resistance to corrosion. Because chromium does not plate readily onto steel, the steel is first plated with nickel and then with chromium.Copper is purified by using impure copper as an anode and pure copper as a cathode, with acidified copper sulfate used as the electrolyte. The impure copper dissolves at the anode and pure copper is deposited on the cathode.

Oxidation + reduction

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