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Windsor University School of Medicine. The extraction of metals To doubt everything or to believe everything are two equally convenient solutions; both dispense with the necessity of reflection. Albert Einstein. Ch.18 J.C. Rowe. Occurrence of metals in nature.
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Windsor University School of Medicine The extraction of metalsTo doubt everything or to believe everything are two equally convenient solutions; both dispense with the necessity of reflection.Albert Einstein Ch.18 J.C. Rowe
Occurrence of metals in nature • Metals occur in rocks referred to as ores. • The metal in an ore is present as cations. • Very few metallic elements are found in the earth as uncombined metals. • Only metals such as gold & platinum are found uncombined with any other element. There are called native metals. • Chemical extraction of a metal from its ore is called smelting.
Metal extraction as reduction • Converting cations to atoms is a process of reduction. • Fe2O3 contains iron (III) ions, Fe3+ . To convert them into metal atoms we must add electrons to them : • Fe3+ + 3e- …………… Fe • Thus the oxidation number has been reduced from +3 to 0.
Smelting involves a struggle for electrons • The electrons which performed the reduction have to come from somewhere else (the reducing agent). • In order for the extraction process to work the metal ion have to win the competition.
Order of reactivity of the metals • The ions of a metal can be reduced by any metal above them in the series. • The higher a metal is in the reactivity series the more energy is needed to reduce its ions.
Methods of producing metals • Electrolysis • Heating with a metal higher in the reactivity series • Heating to a high temperature with carbon • Simple heating • No extraction needed as the metal occurs naturally.
Electrolysis • The passage of an electricity current through an electrolyte, producing a chemical change, is called electrolysis. • A cathode is the electrode of an electrochemical cell at which reduction occurs. • In an electrolytic cell the cathode is negatively charges. • In a galvanic cell the cathode is positively charged. • The oppositely charged electrode is referred to as the anode
Electrolytes vs. non-electrolytes • Solutions through which an electric current can flow are called electrolytes. • Solutions which do not allow a current to pass are non-electrolytes. • Solutions of covalent substances are non-electrolytes • If an ionic material is melted, its ions are free to move through the liquid just as they are in a solution.
Carbon as a reducing agent • Carbon is a good reducing agent. This means carbon is good at taking oxygen away from other molecules. • Under the right conditions, carbon can be oxidised to carbon monoxide. 2C (s) + O2 (g)……… 2CO (g) • The carbon monoxide gas can then be used to reduce an ore : Fe2O3 (s) + 3CO3 (g)→ 2Fe(s) + 3CO2 (g)
Carbothermal reduction • Producing carbon monoxide from carbon can be done at temperatures above 800 C, in a limited supply of air or oxygen. • Reducing an ore by mixing it with carbon & heating the mixture is a process called carbothermal reduction. • The form of carbon used is coke
Smelting • Copper, lead, zinc are all found as sulphide ores. They all occur below carbon in our reactivity series, and so we would expect that they can be extracted by heating their ores with carbon. • Zinc & lead are often found together & are smelted by carbothermal reduction. Heating the sulphides in air converts them to oxides, which then react with carbon to give the metal & carbon dioxide
Luther Eisenhardt It is the attitude of mind developed in the student as he proceeds with his studies, and not primarily the information he acquires, which determine the character and extent of his education.