Presentation on theme: "Hydrocarbons Hydrocarbons are substances that contain Hydrogen and Carbon only. Hydrocarbons are divided into a series of families or groups called Homologous."— Presentation transcript:
Hydrocarbons Hydrocarbons 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.
The Alkanes The Alkanes have a general formula of C n H 2n+2 They run from C 1 –C 60 approx. C 1 -C 4 are gases C 5 -C 17 are liquids C 17 -C 60 are Waxy Solids As we progress between successive members of the series we find that there is a difference of CH 2 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.
The Alkane members Name Molecular FormulaCommon Uses MethaneCH 4 Nat.Gas.Household heating & cooking EthaneC2H4C2H4 PropaneC3H6C3H6 Portable cooking and Heating gas ButaneC 4 H 10 Lighter fuel/Calor Gas PentaneC 5 H 12 HexaneC 6 H 14 Octane* C 8 H 18 Petrol derivative Diesel*C 17 H 36 Transport Bitumen*>C 60 Road/Playgrounds
The Alkenes The Alkenes are another Homologues Series with General Formula C n H 2n All Alkenes must have a C=C double bond. As a result the first member of the series is Ethene ie. Methene does not exist. EtheneC2H4C2H4 PropeneC3H4C3H4 ButeneC4H8C4H8 PenteneC 5 H 10 HexeneC 6 H 12 Only the first three are gases Ethene & propene are important starting materials in making other chemicals
The Cycloalkanes The Cycloalkanes are another Homologous series with General Formula C n H 2n The 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. C n H 2n but that the Cyloalkanes are Saturated whereas the Alkenes are Unsaturated
Isomers Isomers 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.
Cracking of Crude Oil Crude Oil is a mixture of Hydrocarbons called Fractions To 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
Cracking of Crude Oil (contd).representation Steel Wool acts as a Catalyst The hot Paraffin vapour is passed over the heated steel wool The gas collected is tested with Bromine water Alkane When an Alkane is cracked one of the products is always Unsaturated C 16 H 34 C 13 H 28 + C 3 H 6 Safety : Beware of Suck-back
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 Br 2 (aq) to both an alkane and alkene. Alkenes quickly decolourise the Br 2 (from brown to clear) whereas alkanes only slowly decolourise the Br 2 in the presence of UV light. Alkene and Bromine water shaken together Alkane and Bromine water shaken together