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 (CH 4 )

Ethane (C 2 H 6 )

Propane (C 3 H 8 )

Butane (C 4 H 10 )

The alkanes Methane CH 4 EthaneC 2 H 6 PropaneC 3 H 8 ButaneC 4 H 10 PentaneC 5 H 12 HexaneC 6 H 14 OctaneC 8 H 18

The alkanes C n H 2n + 2 Methane CH 4 EthaneC 2 H 6 PropaneC 3 H 8 ButaneC 4 H 10 PentaneC 5 H 12 HexaneC 6 H 14 OctaneC 8 H 18 General formula Homologous group – similar chemical properties, structures and functional groups

The alkanes C n H 2n + 2 Methane CH 4 EthaneC 2 H 6 PropaneC 3 H 8 ButaneC 4 H 10 PentaneC 5 H 12 HexaneC 6 H 14 OctaneC 8 H 18 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

Hydrocarbons burn producing carbon dioxide and water CH 4 + 2O 2 CO 2 + 2H 2 O

Incomplete combustion When there is insufficient oxygen, carbon monoxide is also formed It reduces the blood’s oxygen carrying capability

Another family!

The alkenes C n H 2n Ethene C 2 H 4 Propene C 3 H 6 Butene C 4 H 8 Pentene C 5 H 10 Hexene C 6 H 12

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 etheneBromine (brown) Dibromoethane (colourless)

Alcohols - ethanol

Alcohols Methanol CH 3 OH Ethanol C 2 H 5 OH Propanol C 3 H 7 OH Butanol C 4 H 9 OH Pentanol C 5 H 11 OH Hexanol C 6 H 13 OH

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

Ethanol and sodium 2C 2 H 5 OH + 2Na 2C 2 H 5 ONa + H 2 Hydrogen and sodium ethoxide formed

Oxidation of ethanol Ethanol can be oxidised to form ethanoic acid (acetic acid = vinegar!)

Dehydration of Ethanol

Ethanol + carboxylic acids Ethanol + ethanoic acid ethyl ethanoate + water An ester (they normally smell nice!)

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 ++ + 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.