Production and Uses of Metals CHEMISTRY 2 Additional Science Chapter 8

Metallic minerals Pyrite (a mineral of iron - sulphide) Haematite (a mineral of iron - oxide) The least reactive metals occur in an uncombined form within the Earth’s crust. The other metals exist as ores in combination with other elements such as oxygen and sulphur. Iron pan Metals are produced from their ores by a process called reduction. e.g. gold Additional Science Chapter 8

The reactivity series of metals Different metals have different reactivities. A more reactive metal will remove oxygen from the oxide of a less reactive metal when a mixture of the two is heated. When a mixture of powdered aluminium and iron(III) oxide is ignited by a high temperature fuse, molten iron is formed. This reaction is called the thermit reaction and is used to weld sections of railway track. crucible A mixture of aluminium and iron(III) oxide reacting together railway track Additional Science Chapter 8

The reactivity series of metals This table shows the reactivity series of common metals, and how they are extracted from their ores. ReactivityElementExtraction methodReaction with acid StrongK (Potassium) Electrolysis Too dangerous Na (Sodium) Ca (Calcium) Releases hydrogen and dilute hydrochloric acid. Mg (Magnesium) Zn (Zinc) Chemical reduction Fe (Iron) Sn (Tin) Cu (Copper) Doesn’t release hydrogen and dilute hydrochloric acid. WeakAg (Silver) Additional Science Chapter 8

Extracting iron from its ore Chemical reduction with carbon 1. Raw materials (iron ore, coke and limestone) are added at the top of the furnace. 1000°C 1500°C 2000°C Blasts of hot air Molten slag (impurities) Outlet for molten iron Outlet for the slag Load if iron ore, coke and limestone Gas outlet Molten iron The blast furnace 2. Blasts of hot air (which give the furnace its name) are blown in near the bottom of the furnace. 3. Oxygen in the blasts of air reacts with coke (carbon) to form carbon monoxide. 2C + O 2  2CO This reaction is very exothermic and the temperature in the furnace reached 2000°C. 4. As the carbon monoxide rises up the furnace, it reacts with the iron ore (iron(III) oxide to form iron. Fe 2 O 3 + 3CO  2Fe + 3CO 2 5. Molten iron runs to the bottom of the furnace. It is tapped off from time to time. 6. The molten iron is used to make steel or poured into moulds to solidify. The large chunks of iron formed are called ‘pigs’ so this metal is called ‘pig iron’.

Steel – properties and uses brittle Iron from the blast furnace is very brittle because it contains up to 4.5% carbon. Mild steel contains approximately 0.5% carbon Most of this iron is converted to steel, which is far more useful, by removing most of the carbon. Mild steel contains approximately 0.5% carbon. Hard steel contains up to 1.5% carbon. Car bodiesTinplate It is possible to treat steel. Heat treatment Creating alloys with other metals Stainless steel (chromium and nickel) Very hard steel (tungsten) Tough steel (manganese) machinesDomestic appliances Additional Science Chapter 8

Recycling steel Steel is recycled on a large scale. Saves up to 50% of energy costs Helps to conserve iron ore Cuts down the emission of greenhouse gases Additional Science Chapter 8

Electrolysis – background Electrolysis is a chemical reaction. Current enters the electrolyte via two solid conductors called electrodes. Conducting liquid – electrolyte Electrodes Additional Science Chapter 8

anodecathode The anode is the positive electrode, and the cathode is the negative electrode. Negative Electrode Positive electrode Electrolyte ion + ion - ion + ion - ion + ion - ion + ion - ions anions) The positive ions (cations) move towards the negative electrode, and the negative ions (anions) move towards the positive electrodes. Electrolysis – background Additional Science Chapter 8

Electrolysis – extraction of reactive metals carbon anodes aluminium oxide in molten cryolite crust of solidified electrolyte Molten aluminium tap hole insulated cell casing carbon lining to cell acting as the cathode Electrolysis of aluminium oxide (alumina) Bauxite – a rock containing aluminium Remove impurities by chemical method Aluminium oxide powder (alumina), with a very high melting point 1. Aluminium oxide is dissolved in molten cryolite (about 950°C). 2. Oxygen gas is formed at the carbon anodes, and at that high temperature the anodes react with oxygen, burning away and having to be replaced from time to time. 3. Aluminium in the form of a molten metal forms at the cathode. 4. The tap hole is used to collect the aluminium, the crust needs to be broken to add more aluminium oxide. Additional Science Chapter 8

The equations for the reaction: Al 3+ +3e Al 2O 2- -4e O 2 Positive aluminium ions are attracted to the negative cathode, where they gain electrons and form aluminium metal. Negative oxide ions are attracted to the positive anode, where they lose electrons and form oxygen gas. Additional Science Chapter 8

Railway links Roads Port A good transport network in and out Nuclear Power Station Hydroelectric Power Source Build aluminium works near cheap sources of electricity A lot of electricity is required for producing the metal via electrolysis The raw materials and the product need to be transported easily Locating aluminium works Additional Science Chapter 8

Properties of aluminium light strong density of 2.7g/cm 3 layer of aluminium oxide (this prevents corrosion even though the metal is very reactive) Using aluminium UseReason 1. High voltage power cables for the National Grid Light, resistant to corrosion 2. Saucepans and kitchen foilGood conductor of heat, non toxic 3. Window frames and greenhousesStrong and light 4. Drinks cansStrong and non toxic 5. Aeroplane and car bodiesStrong and resistant to corrosion resistant to corrosion Additional Science Chapter 8

Properties of copper excellent conductor of electricity and heat malleable ductile non toxic Use of copper UseReason 1. Wires in electrical circuitsGood conductor of heat 2. SaucepansGood conductor of heat and non toxic 3. JewelleryMalleable and ductile, attractive colour and lustre 4. Water pipesNon toxic and malleable 5. Produces the alloy bronze (copper + tin) and brass (copper + zinc) Additional Science Chapter 8

Properties of titanium good conductor of heat and electricity light tough non toxic Using titanium UseReason 1. Aircraft industryLight, tough, non corrosive 2. Surgical equipmentLight, tough, non corrosive 3. Artificial joints, plates for bone fractures Non toxic, light, tough, non corrosive 4. JewelleryNon toxic 5. Titanium dioxide is the basis of white paint. non corrosive strong high melting point low density Additional Science Chapter 8

Fluctuations in the cost of metals can affect the economy. The consequences of metal extraction When the ore runs out, the mine workings may be abandoned causing a deterioration of the landscape. Important for the economy (Economic boom in the UK during Industrial Revolution). Extraction and processing of minerals creates employment. Importing metals is very expensive for the country. Processing minerals have a detrimental effect on the environment. A lot of electricity is needed to produce aluminium. Many minerals are sulphides – produce sulphur dioxide (the gas that causes acid rain). Sometimes less useful and toxic metals are found with the ones that are needed. Advantages Disadvantages Additional Science Chapter 8