Notes On Refining Techniques And Uses Of Metals - ICSE Class 10 Chemistry
A metal extracted from its ore by any method is generally impure and is known as crude metal. The impure metal is purified by subjecting it to a process of purification or refining. Depending upon the nature of the metal and the impurity present, various refining methods, such as distillation, liquation, electrolysis, zone refining, vapour phase refining and chromatography, are used. Distillation is refining a metal by evaporating it and then re-liquefying it. In this method an impure metal with a low melting point is heated at just enough temperature to melt it using a sloping hearth. The impurities with higher melting points do not melt and stay at the top of the sloping surface, while the molten metal flows down, thereby separating it from the impurities. Liquation is passing molten metal over a sloping hearth so that it is separated from the solid impurities. In electrolytic refining, a strip of impure metal is used as the anode, a pure metal strip as the cathode and a solution of the metal as the electrolyte. The impurities gather at the anode and the pure metal at the cathode. When a heated roller is passed over an impure metal rod, the impurities shift with the roller toward the right and pure metal crystallises on the left side. This technique is known as zone refining. In vapour phase refining, a metal is converted into its volatile compound, which is then decomposed to give the pure metal. In chromatography method, the metals and the impurities are separated by the difference in their relative adsorption with an adsorbing medium. The mixture to be separated is applied onto a stationary phase and a mobile phase is allowed to run slowly over the stationary phase. The components in the mixture get partitioned between the mobile phase and the stationary phase, and thus, get separated. Depending upon the physical state of the mobile phase and the stationary phase, and also on the passage of the mobile phase, different chromatographic methods such as paper chromatography, column chromatography and gas chromatography are used. Applications of Metals: Aluminium foils are used as wrappers for chocolates, medicines and food items. Aluminium is used to make electrical wires as it is a very good conductor of electricity. Aluminium alloys are light, and are very useful. Copper is used for making electrical wires. Copper pipes are used in homes and industries to carry water and steam. Copper forms alloys such as brass with zinc, bronze with tin and coinage with nickel. Zinc is used for galvanising iron. Zinc is extensively used in carbon-zinc dry cells or batteries. Zinc forms alloys such as brass with copper, and German silver with copper and nickel. Zinc dust is used as a reducing agent in the manufacture of dye-stuffs and paints. Cast iron, the most important form of iron, is used for casting stoves, railway sleepers, toys and gutter pipes. An important alloy of iron is steel, which has many domestic and industrial uses.

#### Summary

A metal extracted from its ore by any method is generally impure and is known as crude metal. The impure metal is purified by subjecting it to a process of purification or refining. Depending upon the nature of the metal and the impurity present, various refining methods, such as distillation, liquation, electrolysis, zone refining, vapour phase refining and chromatography, are used. Distillation is refining a metal by evaporating it and then re-liquefying it. In this method an impure metal with a low melting point is heated at just enough temperature to melt it using a sloping hearth. The impurities with higher melting points do not melt and stay at the top of the sloping surface, while the molten metal flows down, thereby separating it from the impurities. Liquation is passing molten metal over a sloping hearth so that it is separated from the solid impurities. In electrolytic refining, a strip of impure metal is used as the anode, a pure metal strip as the cathode and a solution of the metal as the electrolyte. The impurities gather at the anode and the pure metal at the cathode. When a heated roller is passed over an impure metal rod, the impurities shift with the roller toward the right and pure metal crystallises on the left side. This technique is known as zone refining. In vapour phase refining, a metal is converted into its volatile compound, which is then decomposed to give the pure metal. In chromatography method, the metals and the impurities are separated by the difference in their relative adsorption with an adsorbing medium. The mixture to be separated is applied onto a stationary phase and a mobile phase is allowed to run slowly over the stationary phase. The components in the mixture get partitioned between the mobile phase and the stationary phase, and thus, get separated. Depending upon the physical state of the mobile phase and the stationary phase, and also on the passage of the mobile phase, different chromatographic methods such as paper chromatography, column chromatography and gas chromatography are used. Applications of Metals: Aluminium foils are used as wrappers for chocolates, medicines and food items. Aluminium is used to make electrical wires as it is a very good conductor of electricity. Aluminium alloys are light, and are very useful. Copper is used for making electrical wires. Copper pipes are used in homes and industries to carry water and steam. Copper forms alloys such as brass with zinc, bronze with tin and coinage with nickel. Zinc is used for galvanising iron. Zinc is extensively used in carbon-zinc dry cells or batteries. Zinc forms alloys such as brass with copper, and German silver with copper and nickel. Zinc dust is used as a reducing agent in the manufacture of dye-stuffs and paints. Cast iron, the most important form of iron, is used for casting stoves, railway sleepers, toys and gutter pipes. An important alloy of iron is steel, which has many domestic and industrial uses.

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