√ Oxidation and reduction | Production of Materials | iitutor

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• published: 18 Feb 2016
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https://www.iitutor.com Electrochemistry • Chemical reactions involve valence (bonding) electrons of atoms. • When electrons are transferred between atoms or groups of atoms, the movement of these electrons can be used to provide electrical energy (batteries). Displacement reaction A reaction in which a metal converts the ion of another less reactive metal to its neutral form. Oxidation –Loss of electrons Reduction – Gain of electrons • Oxidation-reduction reactions are sometimes referred to as redox (reduction/oxidation) reactions. • The mnemonics OIL RIG (Oxidation is loss, Reduction is gain) help when studying redox reactions. • There are many different types of cells used as sources of electrical energy. They can be single-use (primary cells) or re-chargeable (secondary cells). These cells vary, considerably in their costs and what they can be used for. When electrons are lost from an atom, it has been oxidised When electrons are gained by an atom, it has been reduced The process of electron loss is oxidation. The process of electron gain is reduction. Metal displacement reactions Displacement reactions are oxidation-reduction reactions in which one of the products is displaced from solution as a separate phase, usually as a solid or a gas. Reactions between a metal and a solution containing the ions of a different metal are called metal displacement reactions. In these reactions the metal dissolves and the ions of the other metal are reduced to elemental metal which deposits out of solution. In the reaction between zinc metal and copper (II) sulfate there is a transfer of electrons from the zinc metal to the copper (II) ions. Note that the sulfate ions are spectator ions. The transfer of electrons from Zn to Cu2+ takes place on the surface of the zinc strip. As the reaction proceeds the zinc metal dissolves and copper metal is formed. As the Cu2+ ions are reduced to Cu metal the blue coloured solution fades, eventually becoming colourless. The Cu2+ ions have a greater tendency to gain electrons than Zn2+ ions. As a result, Cu2+ ions will accept electrons from atoms of Zn metal, resulting in the formation of Cu atoms and Zn2+ ions. The following half-equations represent the two simultaneous processes occurring during this reaction. The reaction which takes place when metallic zinc is placed in a solution of lead(II) nitrate is another metal displacement reaction. In this reaction the zinc dissolves and beautiful shiny grey crystals of metallic lead deposit from the solution. In both of the reactions considered above, a metallic ion is displaced from solution by another metal which goes into solution as oxidised metal ions. The metallic ion that is reduced has a greater tendency to gain electrons than the metal ions formed by the metal which dissolves. Thus Cu2+ ions have a greater tendency to gain electrons than Zn2+ ions. Similarly, Pb2+ ions gain electrons more readily than Zn2+ ions. Displacement reactions and the Activity series Metals were ranked in order of reactivity by comparing their reactivities with oxygen, water and acids. Metals can also be arranged into an activity series by their ability to displace one another from solution. If a strip of copper is placed in a solution of zinc sulfate no reaction occurs. This is because Zn2+ ions have a lesser tendency to gain electrons (be reduced) than Cu2+ ions. As a result, Cu atoms will not give up electrons to Zn2+ ions.