Topics 3abc – Alkanes, alkenes and ethanol Topics 5bc – natural oil and gas and synthetic...
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Transcript of Topics 3abc – Alkanes, alkenes and ethanol Topics 5bc – natural oil and gas and synthetic...
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
• Butane C4H10
• Pentane C5H12
• Hexane C6H14
• Octane C8H18
General formula
Homologous group – similar chemical properties, structures and functional groups
The alkanes CnH2n + 2
• Methane CH4
• Ethane C2H6
• Propane C3H8
• Butane C4H10
• Pentane C5H12
• Hexane C6H14
• Octane C8H18
General formula
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
ethene Bromine (yellow/orange)
Dibromoethane (colourless)
Alcohols - ethanol
Alcohols
• Methanol CH3OH
• Ethanol C2H5OH
• Propanol C3H7OH
• Butanol C4H9OH
• Pentanol C5H11OH
• Hexanol C6H13OH
Alcohols
• Methanol CH3OH
• Ethanol C2H5OH
• Propanol C3H7OH
• Butanol C4H9OH
• Pentanol C5H11OH
• Hexanol C6H13OH
“functional group”
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
• Propanoic acid C3H5OOH
• Butanoic acid C4H7OOH
• Pentanoic acid C5H9OOH
• Hexanoic acid C6H11OOH
“functional group”
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 – NylonDiamine + dicarboxylic acid
+ + + monomers
Reactive ends
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.