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Topics 3abc – Alkanes, alkenes and ethanol Topics 5bc – natural oil and gas and synthetic polymers. Crude oil (Petroleum). A mixture of hydrocarbons (chemicals which contain only hydrogen and carbon atoms). Fractional distillation. Separation of liquids with different boiling points. - PowerPoint PPT Presentation
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Topics 3abc Alkanes, alkenes and ethanolTopics 5bc natural oil and gas and synthetic polymers
Crude oil (Petroleum)A mixture of hydrocarbons (chemicals which contain only hydrogen and carbon atoms)
Fractional distillationSeparation of liquids with different boiling points
Fractional distillationThe mixture can be split into simpler fractions by fractional distillation
Welcome to a new family
The alkanes
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)
The alkanesMethane CH4EthaneC2H6PropaneC3H8ButaneC4H10PentaneC5H12HexaneC6H14OctaneC8H18
The alkanes CnH2n + 2Methane CH4EthaneC2H6PropaneC3H8ButaneC4H10PentaneC5H12HexaneC6H14OctaneC8H18General formulaHomologous group similar chemical properties, structures and functional groups
The alkanes CnH2n + 2Methane CH4EthaneC2H6PropaneC3H8ButaneC4H10PentaneC5H12HexaneC6H14OctaneC8H18General formulaHomologous group similar chemical properties, structures and functional groupsGenerally unreactive, but burn exothermically. Longer chains burn less easily.
Structural formulae
Alkanes are saturated compoundsNo double bonds
Tetrahedral bondsIn alkanes, the carbon bonds are tetrahedral
Chlorinated methaneMethane can be chlorinated. Trichloromethane is commonly known as chloroform.
IsomersSame formula, but different structuresWe have slighty different physical properties (longer chains have higher boiling points)
Combustion
CombustionHydrocarbons burn producing carbon dioxide and waterCH4 + 2O2CO2 + 2H2O
Incomplete combustionWhen there is insufficient oxygen, carbon monoxide is also formedIt reduces the bloods oxygen carrying capability
Another family!
The alkenes CnH2nEthene C2H4Propene C3H6Butene C4H8Pentene C5H10Hexene C6H12
The alkenesUnsaturated (contain a double bond)More reactiveCan add atoms addition reactions
Alkenes - equilateralThe bonds on a double bonded carbon in an alkene point towards the corners of an equilateral triangle
Test for alkenesDecolourises bromine wateretheneBromine (brown)Dibromoethane (colourless)
Alcohols - ethanol
AlcoholsMethanol CH3OHEthanol C2H5OHPropanol C3H7OHButanol C4H9OHPentanol C5H11OHHexanol C6H13OH
Ethanol Can be made by the addition reaction of water to ethene when you have plenty of oilPhosphoric acid
Ethanol - Fermentation of sugarsYou can make ethanol for industry this way when you have lots of sugar cane
Ethanol and sodium2C2H5OH + 2Na 2C2H5ONa + H2
Hydrogen and sodium ethoxide formed
Oxidation of ethanolEthanol can be oxidised to form ethanoic acid (acetic acid = vinegar!)
Dehydration of Ethanol
Ethanol + carboxylic acidsEthanol + ethanoic acid ethyl ethanoate + waterAn ester (they normally smell nice!)
Polymers
Polymers addition polymerisationMolecules of ethene can be joined together to form polyethene monomers polymer
Polythene
Polypropylene Strong and resistant to chemicals
poly(chloroethene) - PVC
Condensation polymers - Nylon+++monomersReactive endspolymerSmall molecules given off (HCl)
Cracking!
Too many long moleculesCrude oil contains too many of the long (and not so useful molecules)
CrackingLuckily we can break the long molecules into shorter ones by cracking
The long molecules are passed over hot broken pot (ceramic) and split up into smaller molecules. A catalyst can also be used
CrackingCracking an alkane produces smaller alkanes and also alkenes.