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.