Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only. Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is The first four members of the alkanes are methane, ethane, propane and butane. Alkane molecules can be represented in the following forms: or than methane, ethane, propane and butane. WS 1.2 Explain what is meant by the formula Make molecular models and work out general formula for the alkanes. Draw the covalent bonding in: methane ethane propane butane. Define the term saturated. Make models of alkane molecules using molecular modelling kits. 5.7.1.2 The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon Explain how fractional distillation works in terms of evaporation and condensation. 2 Describe the process of fractional distillation. Grade 9: explain the process of fractional distillation in terms of Research uses of the fractions of crude oil. Video clips YouTube: YouTube:
5.7.1.3 Some properties of hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability. These properties influence how hydrocarbons are used as fuels. The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water. Recall how boiling point, viscosity and flammability change with increasing molecular size. Write balanced equations for the complete combustion of hydrocarbons with a given formula. Knowledge of trends in properties of hydrocarbons is limited to: boiling points viscosity flammability. WS 1.2, 4.1 1 Explain the properties of hydrocarbons in relation to intermolecular forces. Write balanced symbol equations for the combustion of hydrocarbon fuels. Describe the balanced symbol equation including moles present, reactants and products. Investigate the properties of different hydrocarbons in terms of boiling point, viscosity and flammability with increasing molecular size. Identify the products of combustion of alkanes. Video clips: 5.7.1.4 Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules. Cracking can be done by various methods including catalytic cracking and steam cracking. Describe in general terms the conditions used for catalytic cracking and steam cracking. Recall the colour change when bromine water reacts with an alkene. 1 Describe the process of cracking. Explain the process of cracking. Write balanced symbol equations for the cracking of alkanes. Demo or practical: crack paraffin over porous clay pot. Use bromine water to identify alkenes. Test for unsaturation in other compounds. Video clips YouTube:
The products of cracking include alkanes and another type of hydrocarbon called alkenes. Alkenes are more reactive than alkanes and react with bromine water, which is used as a test for alkenes. There is a high demand for fuels with small molecules and so some of the products of cracking are useful as fuels. Alkenes are used to produce polymers and as starting materials for the production of many other chemicals. Balance chemical equations as examples of cracking given the formulae of the reactants and products. Give examples to illustrate the usefulness of cracking. Be able to explain how modern life depends on the uses of hydrocarbons. For Combined Science: Trilogy and Synergy students do not need to know the formulae or names of individual alkenes. WS 1.2 Describe the balanced symbol equation including moles present, long alkane reactant, specific reaction conditions, and alkene and short alkane products. Research uses of common alkenes.