2 HydrocarbonsHydrocarbons are substances that contain Hydrogen and Carbon only.Hydrocarbons are divided into a series of families or groups called Homologous Series.A Homologous Series is a group of compound which have a General Formula and are chemically similar.Examples of Homologous Series are the: Alkanes, Alkenes and Cycloalkanes.
3 The Alkanes The Alkanes have a general formula of CnH2n+2 They run from C1 –C60 approx.C1-C4 are gasesC5-C17 are liquidsC17-C60 are Waxy SolidsAs we progress between successive members of the series we find that there is a difference of CH2 in their formulae. As a direct result there is a regular increase in their Boiling Points since more energy is required to break up the longer chains.All Alkanes are flammable, have a pH of 7 and are insoluble in water.
4 The Alkane members Name Methane CH4 Ethane C2H4 Propane C3H6 Butane Molecular FormulaCommon UsesMethaneCH4Nat.Gas.Household heating & cookingEthaneC2H4PropaneC3H6Portable cooking and Heating gasButaneC4H10Lighter fuel/Calor GasPentaneC5H12HexaneC6H14Octane* C8H18Petrol derivativeDiesel*C17H36TransportBitumen*>C60Road/Playgrounds
5 Only the first three are gases The AlkenesThe Alkenes are another Homologues Series with General Formula CnH2nAll Alkenes must have a C=C double bond.As a result the first member of the series is Ethene ie. Methene does not exist.Ethene & propene are important starting materials in making other chemicalsEtheneC2H4PropeneC3H4ButeneC4H8PenteneC5H10HexeneC6H12Only the first three are gases
6 The CycloalkanesThe Cycloalkanes are another Homologous series with General Formula CnH2nThe Cycloalkanes are Ring compounds which means that the first member of the series is cyclopropane.It should be noted that the Cycloalkanes have the same general formula as the alkenes i.e. CnH2n but that the Cyloalkanes are Saturated whereas the Alkenes are Unsaturated
7 IsomersIsomers are molecules with the same Molecular formula but different structural formula.Note: There must be the same number of carbon and hydrogen atoms but there also must be a completely different arrangement of Carbon atoms.
8 Cracking of Crude OilCrude Oil is a mixture of Hydrocarbons called FractionsTo Separate the oil into its component fractions we first boil it. This process is called Fractional Distillation.After Fractional Distillation there are a large number of Long-Chain Hydrocarbons left.To meet market demand these long-chain Hydrocarbons are broken up into smaller more desirable Hydrocarbon Chains ie they are said to be Cracked
9 Cracking of Crude OilSteel Wool acts as a CatalystThe gas collected is tested with Bromine waterThe hot Paraffin vapour is passed over the heated steel woolSafety:Beware of Suck-backWhen an Alkane is cracked one of the products is always UnsaturatedC16H34C13H28 + C3H6
10 The Test for Saturation/Unsaturation An Unsaturated compound is one that contains a C=C double bond.A Saturated compound is one that contains C-C single bonds only.Alkanes are Saturated and Alkenes Unsaturated.The Test: Add Br2(aq) to both an alkane and alkene. Alkenes quickly decolourise the Br2(from brown to clear) whereas alkanes only slowly decolourise the Br2 in the presence of UV light.Alkene and Bromine water shaken togetherAlkane and Bromine water shaken together
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