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
Fractional distillation The 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 alkanes Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12 Hexane C6H14 Octane C8H18
The alkanes CnH2n + 2 Methane CH4 Ethane C2H6 Propane C3H8 General formula The alkanes CnH2n + 2 Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12 Hexane C6H14 Octane C8H18 Homologous group – similar chemical properties, structures and functional groups
The alkanes CnH2n + 2 Methane CH4 Ethane C2H6 Propane C3H8 General formula The alkanes CnH2n + 2 Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12 Hexane C6H14 Octane C8H18 Homologous group – similar chemical properties, structures and functional groups Generally unreactive, but burn exothermically. Longer chains burn less easily.
Structural formulae
Alkanes are saturated compounds No double bonds
Tetrahedral bonds In alkanes, the carbon bonds are tetrahedral
Chlorinated methane Methane can be chlorinated. Trichloromethane is commonly known as chloroform.
Isomers Same formula, but different structures We have slighty different physical properties (longer chains have higher boiling points)
Combustion
Combustion Hydrocarbons burn producing carbon dioxide and water CH4 + 2O2 CO2 + 2H2O
Incomplete combustion When there is insufficient oxygen, carbon monoxide is also formed It reduces the blood’s oxygen carrying capability
Another family!
The alkenes CnH2n Ethene C2H4 Propene C3H6 Butene C4H8 Pentene C5H10 Hexene C6H12
The alkenes Unsaturated (contain a double bond) More reactive Can “add” atoms – addition reactions
Alkenes - equilateral The bonds on a double bonded carbon in an alkene point towards the corners of an equilateral triangle
Test for alkenes Decolourises bromine water Dibromoethane (colourless) ethene Bromine (yellow/orange)
Alcohols - ethanol
Alcohols Methanol CH3OH Ethanol C2H5OH Propanol C3H7OH Butanol C4H9OH Pentanol C5H11OH Hexanol C6H13OH
Alcohols Methanol CH3OH Ethanol C2H5OH Propanol C3H7OH Butanol C4H9OH “functional group” Methanol CH3OH Ethanol C2H5OH Propanol C3H7OH Butanol C4H9OH Pentanol C5H11OH Hexanol C6H13OH
Ethanol Can be made by the addition reaction of water to ethene – when you have plenty of oil Phosphoric acid
Ethanol - Fermentation of sugars You can make ethanol for industry this way when you have lots of sugar cane
Dehydration of Ethanol
Ethanol and sodium 2C2H5OH + 2Na 2C2H5ONa + H2 Hydrogen and sodium ethoxide formed
Oxidation of ethanol Ethanol can be oxidised to form ethanoic acid (acetic acid = vinegar!)
Carboxylic acids Methanoic acid CHOOH Ethanoic acid C2H3OOH Propanoic acid C3H5OOH Butanoic acid C4H7OOH Pentanoic acid C5H9OOH Hexanoic acid C6H11OOH
Carboxylic acids Methanoic acid CHOOH Ethanoic acid C2H3OOH “functional group” Methanoic acid CHOOH Ethanoic acid C2H3OOH Propanoic acid C3H5OOH Butanoic acid C4H7OOH Pentanoic acid C5H9OOH Hexanoic acid C6H11OOH
Ethanol + ethanoic acid acids Ethanol + ethanoic acid ethyl ethanoate + water An ester (they normally smell nice!)
Ethyl ethanoate – an “ester”
Polymers
Polymers – addition polymerisation Molecules of ethene can be joined together to form polyethene ← monomers ← polymer
Polythene
Polypropylene – Strong and resistant to chemicals
poly(chloroethene) - PVC
Condensation polymers – Nylon Diamine + dicarboxylic acid Reactive ends + + + monomers polymer Small molecules given off (HCl)
Cracking!
Too many long molecules Crude oil contains too many of the long (and not so useful molecules)
Cracking Luckily 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
Cracking Cracking an alkane produces smaller alkanes and also alkenes.