Products from rocks (summary of the AQA module)
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The document summarizes information about products made from rocks and extracting metals and fuels from raw materials. It discusses how limestone decomposes into quicklime and carbon dioxide when heated, and how quicklime forms calcium hydroxide when mixed with water. It also explains how crude oil is separated into fractions by fractional distillation, and how burning fuels produces gases like carbon dioxide, water vapor, carbon monoxide and sulfur dioxide.
Products from rocks (summary of the AQA module)
- 1. Products from rocks Revision summary 15 February 2011
- 2. Atoms, elements and compounds All substances are made up of atoms . Elements contain only one type of atom. The atom has a central core called the nucleus and this is surrounded by fast moving electrons . Atoms form chemical bonds by giving taking or sharing electrons – the new substance formed is a compound . All atoms have their own symbols and are shown on the periodic table. 1
- 3. Chemistry of limestone Limestone is calcium carbonate (CaCO 3 ), it is a solids white compound. Limestone is used in buildings. Limestone decomposes(thermal decomposition) when heated into quicklime or calcium oxide (CaO) and carbon dioxide (CO 2 ). Other metal carbonates also decompose on heating. 2
- 4. Quicklime and slaked lime If water is added to quicklime (CaO) a lot of heat is released and slaked lime or calcium hydroxide Ca(OH) 2 is formed. Slaked lime, sand and water form mortar. This has been used in building for thousands of years. The reaction is: Slaked lime + CO 2 = calcium carbonate + water . 3
- 5. Cement, concrete and glass Heating limestone with clay in a kiln produces cement – this hardens much faster than slaked lime mortar. Concrete is a mixture of stones, sand cement and water. It can be reinforced with steel bars and is very strong. Glass is made by heating limestone, sand and sodium carbonate. 4
- 6. Extracting metals Metals are usually found combined with other elements in ores but a few like gold and silver are found naturally (native state). The reactivity series shows a list of metals from most reactive to least reactive. Metal oxides can be reduced to the metal and carbon dioxide using carbon. Metal oxide + carbon = metal + carbon dioxide 5
- 7. Extracting iron Iron ore (haematite or iron oxide) can be extracted with carbon (coke) in a blast furnace. Limestone is also added to remove sand in the mix as it forms slag. Reactions are: C + O 2 =CO 2 CO 2 + C = CO Fe 2 O 3 + 3CO = 2Fe + 3CO 2 6
- 8. Properties of iron and steel Iron made in a blast furnace is 96% pure, it is called pig iron and is very brittle. The carbon is removed from the impure iron and other elements are added to make steel. Steels made with chromium and nickel as alloys are called stainless steel. This type of steel does not rust and is very hard. 7
- 9. Using alloys Bronze is made from copper and tin – low friction metal. Brass is made from copper and zinc and is very hard and strong. Gold is alloyed to make it harder. Smart alloys are able to retain their shape – they are used in medicine and dentistry to help move teeth and bones into the correct position. 8
- 10. Transition metals The transition metals area large block of metals in the middle of the periodic table. Their properties include being good conductors of heat and electricity, hard, strong and malleable (bend into shapes). These properties make these metals ideal for use in construction and manufacturing transport vehicles. 9
- 11. Copper Copper is the most useful metal in conduction of electricity. It is extracted from its ore by reacting with sulphuric acid or smelting (heating) followed by electrolysis. The above processes use vast amounts of heat and electricity so are not environmentally friendly and expensive. New methods using bacteria or fungi are being investigated. 10
- 12. Aluminium Aluminium has a very low density and is a good conductor of heat and electricity. Aluminium does not corrode easily but in its natural state is not very strong, however when it is alloyed with other metals it becomes harder and stronger. Aluminium is a very reactive metal so it has to be extracted from bauxite (aluminium oxide) ore by electrolysis – this an expensive process. 11
- 13. Titanium Titanium is a silvery white, strong and non corrosive metal. It has a very high melting point (1660 o C) which makes it especially useful. It is produced by displacement by a more reactive metal such as magnesium or sodium. It is used for jet engines, aircraft bodies, in nuclear reactors and for human joint replacements. 12
- 14. Fuels from crude oil Crude oil contains a mixture of hydrocarbon molecules. Most of the hydrocarbons in crude oil are alkanes – these have the general formula C n H 2n+2 . Since there are no carbon carbon double bonds in alkanes the molecules are said to be saturated (cannot bond onto any more atoms) 13
- 15. Fractional distillation Crude oil is separated into different fractions, containing molecules of different sizes by fractional distillation. Small molecules have lower boiling points, are of low viscosity (runny), more volatile and flammable, so they are better fuels. Crude oil vapour is fed into a fractionating column with lower boiling point gases coming off high up the column. Bitumen for tar road is the highest boiling point fraction. 14
- 16. Burning fuels When a fuel is burnt in an oxygen rich environment carbon dioxide and water vapour are produced. If too little oxygen is present poisonous carbon monoxide (CO) is produced. Fuels also produces sulphur dioxide which make acid rain and nitrogen dioxide as well as carbon particles (particulates) 15
- 17. Cleaner fuels Carbon dioxide gas from burning fuels is a greenhouse gas. This gas warms the Earth by reducing heat loss from the atmosphere. The pollution produced by gases such as carbon monoxide, sulphur dioxide and nitrogen oxides can be reduced by treating these gases as they are produced – examples are catalytic converters and desulphurisation chemicals. 16