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Smart Teach Chemistry Section 5

Learn about hydrocarbon fuels, fractional distillation, biofuels, cracking, combustion, polymers, and the disposal of waste plastics in this comprehensive chemistry section.

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Smart Teach Chemistry Section 5

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  1. Smart Teach Chemistry Section 5 Fuels

  2. Making crude oil useful Fuels are substances that react with oxygen to produce useful energy. Hydrocarbon fuels are fuels that contain onlyhydrogen and carbon atoms. (marks are given for the word only!) They are obtained from the fractional distillation of crude oil. Each fraction of crude oil contains a mixture of different hydrocarbon molecules of a similar size and with similar properties.

  3. What is fractional distillation? Fractional distillation is a process used to separate a mixture of liquids that have different boiling points. Fractional distillation is used to separate crude oil into useful products called fractions. It can be done industrially and in the laboratory. You must know the order of the fractions and their uses – shown on the next slide.

  4. Fractional diction of crude oil.

  5. Exam question

  6. Answer

  7. What are biofuels? Biofuels are renewable fuels produced from plant material, such as crops, or animal oils. Bioethanol and biodiesel are types of biofuels used in vehicles to reduce the demand for petrol.

  8. Exam question • (ii)  Bioethanol is a biofuel. • Describe why it is an advantage to use bioethanol rather than petrol as a fuel for car engines. (2)

  9. Answer

  10. Cracking Long-chain hydrocarbon molecules can be broken down into smaller, more useful molecules using a catalyst. This is called catalytic cracking. Catalytic cracking requires: • high temperatures • a catalyst. During cracking, the molecules break apart, forming smaller more useful alkanes and alkenes.

  11. Alkenes can be obtained by cracking some fractions obtained from crude oil. • Explain what is meant by cracking. • (2)

  12. Saturated vs. unsaturated Alkanes are examples of saturated hydrocarbons. A saturated compound only contains single covalent bonds between carbon atoms. Alkenes are examples of unsaturated hydrocarbons. An unsaturated compound contains at least one double covalent bond between carbon atoms. A test to distinguish between saturated and unsaturated compounds is to add bromine water. In the presence of unsaturated compounds, the colour changes from orange to colourless. DO NOT PUT CLEAR!

  13. Bromine water is used to distinguish between alkenes and alkanes. Describe what would be seen when an alkene and an alkane are shaken with separate samples of bromine water. (3) alkene alkane

  14. Sulfur dioxide Sulfuris found naturally in all fossil fuels – fuel oil and coal contain about 2% sulfur. When a hydrocarbon fuel containing sulfur impurities is burned, the sulfur reacts with oxygen and sulfur dioxide (SO2)is produced. SO2dissolves in rain water to produce acid rain.

  15. Describe how impurities in fossil fuels result in the formation of acid rain. • (2)

  16. carbon dioxide + + hydrocarbon oxygen  water What is combustion? When a substance burns, it is said to combust. Complete combustion means that there is enough oxygen available for all of the carbon atoms in a fuel to burn and form carbon dioxide. The word equation for the complete combustion of a hydrocarbonfuel is: If there is a shortage of oxygen when a hydrocarbon fuel is burned, incomplete combustion takes place.

  17. What are polymers? Polymers are very large molecules made when hundreds of monomers join together to form long chains.

  18. Drawing polymers – shorthand formulae Polymers contain thousands of molecules, so how can their structures be easily drawn? Part of the polymer molecule can be drawn: A better way is to show a shorthandformula: The ‘n’ means that the polymer contains a very large number of the repeating unit shown in the brackets.

  19. What happens to waste plastic? Micro-organisms are unable to break down most types of plastic. Plastic is generally non-biodegradable. In the UK, 3.5 million tonnes of plastic packaging is thrown away each year. Plastic litter can cause significant harm to animals and birds. There are three ways to dispose of waste plastics: • landfill • incineration (burning) • recycling.

  20. Waste poly(ethene) can cause problems. • Explain the problems caused by waste poly(ethene). • (2)

  21. An explanation linking two of the following points: • non-biodegradable(1) • (therefore) does not rot / does not break down / disintegrate(1) • lasts for a long time / stays there(1) • fills up landfill (sites)(1) • (causes) litter / looks unattractive (1) • causes pollution (1) • can be a danger to wildlife (1) • produces gases when burnt (1) • a gas mentioned as a result of burning linked to the environmental problem it causes eg carbon dioxide is a greenhouse gas, some gases are toxic (1)

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