Petrochemicals Topic 2 - Chemistry Teaching Resources

KHS Nov 2013 page 1

Petrochemicals Topic 2

These sheets belong to

Petrochemicals

KHS Nov 2013 page 2


There are a number of videos / animations relevant to this topic available on the website.

www.new.chemistry-teaching-resources.com/S3Topic2Media.html

Some of these may be used in class whilst others are optional enhancements or could be watched at home if a particular lesson is missed.

Tick when you have watched

2.1 Fossil Fuels Video - Fossil Fuels Video - Extraction of Oil Flash - Candle Burning Video - Methane Can Video - Methane Explosion Video - Carbon Monoxide Poisoning Video - Cartalytic Converter

2.2 The Alkanes Video - Alkane Structures Video - Alkane Isomers Flash - Naming Alkane Isomers

2.3 Oil Fractions Video - Crude Oil Video - Oil Refining Video - Flammability Video - Viscosity

2.4 Other Families Video - Bromine Test Video - Cracking Hydrocarbon Video - Alkene Structures Video - Ring Molecules Video - Cracking Molecular Video - Saturated / Unsaturated

2.5 Introduction to Plastics Video - Making Plastics - Nylon Video - Making Plastics - Slime Video - Plastics Pollution Video - Plastics to Oil

2.6 Addition Polymerisation Flash - Addition Polymerisation Flash - Addition Polymers

KHS Nov 2013 page 3


VideoFossilFuels

VideoExtraction

of Oil

2.1 Fossil Fuels

Formation of fuels Coal , Oil and Gas are our Fossil Fuels. From Oil come other fuels like petrol, diesel and paraffin.

Formation of Coal

Most of the Coal we usetoday, was formed about250 million years ago. Much of the world wascovered in tropical swamps and forests . As theplants died they were covered with layers of mud and sand . As thelayers built up, the decaying plants were subjected to high pressure / high temperaturefor millions of years, until they turned into coal. Coal is mainly the element carbon .

Formation of Oil & Gas

Oil and gas were formed about 150 million years ago ( when dinosaurs still roamed the earth). They were formed when very small sea animals and plants ( called plankton ) died and fell to the sea bed. The remains were covered with layers of sand and mud .Eventually, because of the great pressure / high temperature , after millions of years, they turned into oial and gas . Crude oil is a mixture of hydrocarbons such as methane ( CH4 ) and paraffin , both members of the Alkane family.

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FlashCandle

Burning

What is a fuel ? A chemical reaction that gives out heat energy is called exothermic.

A fuel is any substance that can be burned to give out heat energy in a controlled and sustained way. Fuels are used for many purposes, e.g. heating our homes, making electricity and for transport.

Burning Charcoal (solid fuel)

Burning Parrafin (liquid fuel)

→ →The water pump is used to suck air over the heated carbon and then through the lime water.

The lime water turns cloudy showing that carbon dioxide has been produced.

carbon + oxygen → carbon dioxide

C + →

parrafinburning

TubeA

TubeB

limewater

to pump

A water pump is used to suck air through the apparatus. The funnel helps to trap the chemicals produced when paraffin burns. Tube A is surrounded with ice to keep it very cold. Water (H2O) condenses in tube A. The lime water in tube B turns cloudy showing carbon dioxide (CO2) has been produced.

The oxygen atoms have come from the air, but the carbon and hydrogen atoms must have been in the paraffin molecules. Paraffin is a hydrocarbon and is one of the many hydrocarbons found in crude oil.

KHS Nov 2013 page 5

Petrochemicals Topic 2Video

MethaneCan

VideoMethane

Explosion

FlashCombustionEquations

Burning Methane (gas fuel)The chemical name for natural gas is methane, and it is one of the most important fuels we have.

PROPERTY OBSERVATIONAppearanceSmell None. (smell added)SolubilityBurningpH

water

methane collecting

from gas tap

Methane is lighter than air so can be collected into an upturned gas jar by slowly displacing the air in the flask. Methane is a neutral gas (pH = 7 ) which burns well to produce water (as shown by the condensation on the walls of the gas jar).

In a good supply of oxygen, carbon dioxide will be produced as complete combustion takes place. (The test for carbon dioxide is that it turns lime water cloudy or milky.)

methane + oxygen → carbon dioxid + watere

CH4 + → + H2OKiller Gas One of the main causes of accidental death in British

homes continues to be carbon monoxide poisoning.

Gas fires, water heaters or gas boilers which burn natural gas ( methane, CH4) are the biggest problem.

methanewaterheater

If not looked after, the air supply can be reduced and, in a poor supply of oxygen, poisonous carbon monoxide can be produced. This is often called incomplete combustion. methane + oxygen → carbon monoxid + watere

CH4 + → + H2OVideoCO

Poisoning

KHS Nov 2013 page 6


exhaustpipe

silencer

stainless steelhousing

ceramic honeycomb structure covered with (expensive) platinum

and rhodium

unburnt petrol,oilcarbon monoxideoxides of nitrogen

nitrogen, oxygenwater vapour

carbon dioxide

Pollution Problems & Solutions

Both coal and oil can lead to pollution problems sometimes on a disastrous scale.

Coal containssulphur , so when it burns, large amounts of sulphur dioxide ( ) enters the air and form acid rain.

Coal and oil produce carbon dioxide which builds up in the atmosphere causing a Greenhouse Effect which may lead to global warming or other climate changes.

All fuels, when they burn in a poor supply of oxygen will produce soot and poisonous carbon monoxide . Cars also produce nitrogen oxides, (acid rain), lead (poisonous) and unburnt hydrocarbons (asthma, cancers etc).

Some solutions to these problems are being tried.

Scrubbing is used to reduce sulphur dioxide emissions from chimneys. Limestone slurry ( awatery mixture) is sprayed into chimneys andreacts with the SO2 to form gypsum, which iseither sold to manufacturers of plaster board, oris dumped in land-fill sites.

Catalytic convertors and new lean burnengines as well as lead-free petrols areall uses to reduce pollution from cars.

However, the only way to reduce carbondioxide is to reduce dramatically the amountof fossil fuels burnt each year.

Carbon monoxide is poisonous because it is the same shape as an oxygen molecule, O2, and attaches itself to a haemoglobin molecule in the red blood cells in the space meant for oxygen.

Too much carbon monoxide leaves the body unable to transport oxygen, and without oxygen it dies.

KHS Nov 2013 page 7


exhaustpipe

silencer

stainless steelhousing

ceramic honeycomb structure covered with (expensive) platinum

and rhodium

unburnt petrol,oilcarbon monoxideoxides of nitrogen

nitrogen, oxygenwater vapour

carbon dioxide

Lead Free Petrol

Lead compounds were added to petrol to stop the petrol igniting too soon. In recent years chemists have made safer chemicals that can be added to petrol.

Most petrol is now lead-free.

Lean Burn Engines The amounts of petrol and air that are mixed in an engine has always been important - but it is almost ‘impossible’ to suck in enough air for complete combustion.

Engineers have worked to develop car engines that can perform just as well but use less petrol for the same amount of air.

These engines are called lean burn engines and the ‘extra’ air, compared to the amount of petrol, allows more complete combustion.

Catalytic Convertors Even modern engines still produce too many pollutants, so special exhaust systems have been developed to try and convert the harmful chemicals into less harmful chemicals.

This is done by making the pollutants react with each other. For example, carbon monoxide can be made to react with nitrogen dioxide to produce less harmful carbon dioxide and harmless nitrogen gas.

carbon + nitrogen n → carbon + nitrogen monoxide monoxyg dioxideere

2CO + 2NO → 2CO2 + N2This requires expensive catalysts and high temperatures, which is why catalytic convertors cannot work until the exhaust has heated up

VideoCatalyticConverter

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2.2 The ALKANES

Alkane Structures

The name’s Ane,

Meth -Ane

007

H|

H — C — H|

H

actual shapeCarbon atoms always have 4 unpaired electrons in their outer shell and so can form 4 bonds.

‘tetrahedral’The bonds keep as far apart as possible; the hydrogen atoms lie at the corners of a pyramid.

structural formulaIt is much easier to draw flat pictures to show how each ofthe atoms are joined to each other.

The alkanes are a family of hydrocarbons; molecules made from carbon and hydrogen atoms only.

The first (smallest) member of the family is methane, CH4.

Having as many as 4 bonds gives carbon atoms the ability to form chains and rings of carbonsatoms. They can also join together with single, C — C, double,C = C, or even triple bonds, C ≡ C.

The Alkane family is made up of chains where all the carbon atoms join together with a single bond.

Alkane Names

1 2 3 4 5 6 7 8Monkeys Eat Peanut Butter Perched High High Overhead

Meth- = 1 Carbon atom Pent- = 5 Carbon atoms

Eth- = 2 Carbon atoms Hex- = 6 Carbon atoms

Prop- = 3 Carbon atoms Hept- = 7 Carbon atoms

But- = 4 Carbon atoms Oct- = 8 Carbon atoms

The surname is -ane to tell you it is a member of the alkane family, the first name tells you the number of carbon atoms in each molecule.

VideoAlkane

Structures

KHS Nov 2013 page 9


CnH

Number of Name of Structural formula Molecular formula carbon atoms alkane

1 methane CH4

2

3

4

The alkanes are called a homologous series of molecules. This is because each molecule differs from the previous molecule by the same amount, —CH2—, ( homo- = same, logous = difference).

H H| |

H — C — C — H| |

H H

H|

H — C — H|

H

This makes it possible to write a General Formula for the alkane family. There are always twice plus two hydrogens for any number of carbon atoms.The table for the Properties of the Alkanes is on page 15

KHS Nov 2013 page 10


Alkane Isomers

Isomers are molecules with the same molecular formula

but have different structuresExample

The alkane hexane has the molecular formula C6 H1 but there are 5 different ways of putting these atoms together - 5 different structures - 5 different isomers .

H H H H H H | | | | | |H — C — C — C — C — C — C — H | | | | | | H H H H H H

The simplest isomer has all 6 carbon atoms in a chain. This would be called n-hexane.

| | | | | — C — C — C — C — C — | | | | | | | | | | — C — C — C — C — C — | | | | |

The next two isomers will have only 5 carbon atoms in the chain.The sixth carbon will be branching off somewhere.2-methyl pentane and3-methyl pentane will be their names

The final two isomers will have only 4 carbon atoms in the chain.The fifth & sixth carbons will be branching off somewhere.2,3-dimethyl butane and2,2-dimethyl butane will betheir names

| | | | — C — C — C — C — | | | | | | | | — C — C — C — C — | | | |

VideoAlkaneIsomers

FlashNamingIsomers



2.3 Oil Fractions

Distillation There is an ever growing demand for the wide range of chemicals produced from Crude Oil.

A special process called refining is needed to separate and collect each of the chemicals.

The chemicals are all hydrocarbons, molecules containing carbon and hydrogen only, so they are very similar. Their different sizes and shapes , however, make them evaporate at different temperatures.

The separating process takes place in large 70 metre high towers; the distillation column.

The crudeoil mixture is heated to a very high temperature, over 350 °C, and enters the column near the bottom. At this temperature, most of the hydrocarbons have changed to gas / vapour.

Only the largest hydrocarbons are still liquid, and they fall to the bottom of the tower.

As the hydrocarbon vapours rise up the tower, theycool down and start to condense back to liquid.

The larger molecules condense lower down while the smaller molecules can travel further up the column before they too are forced to condense.

Groups of hydrocarbons of similar size condense at the same level and form the smaller mixtures we call fractions.

The bubble caps force the vapour to bubble up through some of the liquid already collected at that level. This makes it very difficult for any vapour to travel further up the column than it should.

Heating the oil to a very high temperature and then letting it cool down in the column allows a continious stream of oil to be processed quickly.

This whole process is called Fractional Distillation.

VideoCrude

Oil

VideoOil

Refining



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2.4 Other Familes - Alkenes & Cycloalkanes

Properties of Alkanes & Alkenes

There are, in fact, three families of hydrocarbons that you will be asked to learn about.

As well as the alkane family there is another family called the alkenes.

Property Alkane family Alkene family

Appearance

Smell

Solubility

Burning

pH

At first sight the alkene family has very similar properties to the alkane family.

A chemical test is needed. Bromine water (bromine dissolved in water) is a clear brown solution. If the bromine reacts the colour will disappear - we say that the bromine has been decolourised.

Alkanes - when bromine water is added, the watery solution sinks to the bottom while the oily alkane floats on top. After mixing, the brown bromine moves into the top layer because it prefers to dissolve in an alkane. Very, very slowly the brown colour fades and eventually disappears - the bromine is decolourised very slowly.

Alkenes - when bromine water is added, the watery solution sinks to the bottom while the oily alkene floats on top. After mixing, the brown bromine moves into the top layer because it prefers to dissolve in an alkene. Immediately the brown colourdisappears - the bromine is decolourised very quickly

VideoBromine

Test



Making Alkenes - Cracking Alkenes were made almost by accident. Oil companies needed more supplies of useful fractions such as petrol.

Fractions like Fuel Oil have larger molecules which are not as useful. Someone had the idea of using heat energy to try and shake these molecules until they began to crack up.

The following apparatus can be used to crack a long chain alkane.

The alkane used was liquid paraffin. The new chemicals produced were gas-es.This means that smaller molecules have been produced.

When mixed with bromine water, the bromine is decolourised immediately.This means that some of the new chemicals produced are alkenes.

The steel wool has helped this reaction take place at a safe temperature, but has not been used up. The steel wool is a catalyst.

In Industry this process is called Thermal Cracking (‘thermal’ to show the need for heat energy) or Cat Cracking (‘cat’ to show the need for a catalyst).

Cracking allows the oil industry to change less useful, long chained alkanes into a more useful mixture of short chained alkanes and alkenes.

VideoCracking

Hydrocarbon



Alkene Structures

actual shapeCarbon atoms always have 4 unpaired electrons in their outer shell and so can form 4 bonds in total.

double bondIn the alkene family, two of the carbon atoms will share two pairs of electrons. This forms a double bond.

structural formulaIt is much easier to draw flat pictures to show how each ofthe atoms are joined to each other.

The alkanes are a family of hydrocarbons; molecules made from carbon and hydrogen atoms only.

The first (smallest) member of the family is ethane, C2H4.

The Alkane family is made up of chains where most of the carbon atoms join together with a single bond, but two of the carbon atoms will have joined with a double bond.

1 2 3 4 5 6 7 8Monkeys Eat Peanut Butter Perched High High Overhead

Pent- = 5 Carbon atoms

Eth- = 2 Carbon atoms Hex- = 6 Carbon atoms

Prop- = 3 Carbon atoms Hept- = 7 Carbon atoms

But- = 4 Carbon atoms Oct- = 8 Carbon atoms

H H| |C = C| |H H

Alkene Names The same system is used to name the alkenes as was used to name the alkanes.

The surname is -ene to tell you it is a member of the alkene family, the first name tells you the number of carbon atoms in each molecule.

VideoAlkene

Structures



Number of Name of Structural formula Molecular formula carbon atoms alkene of alkene of alkene

2 ethene C2H4

3

4

5

H H| |C = C| |H H

H H | | H — C = C — C — H | | H H

The alkenes are called a homologous series of molecules. This is because each molecule differs from the previous molecule by the same amount, —CH2—, ( homo- = same, logous = difference).

CnHThis makes it possible to write a General Formula for the alkene family. There are always twice as manyo hydrogens atoms for any number of carbon atoms.

This is different from the alkane family. Since they have no double bond, there is room for two extra hydrogen atoms on an alkane with the same number of carbon atoms.

CnH



Example The alkene pentenee has the molecular formula C6 H1 but there are more than 5 different ways of putting these at-oms together - > 5 different isomers .(Pentane has only 3 isomers)

H H H | | | H — C — C — C — C = C — H | | | | | H H H H H

The simplest isomer have all 5 carbon atoms in a chain, but...

.......... there are 2 different positions for the double bond

| | | — C — C — C = C — C — | | | | |

The next three isomers will have only 4 carbon atoms in the chain.

The fifth carbon will be branching off somewhere.

Again, the different possiblepositions of the double bond allowfor more isomers.

| | — C — C — C = C — | | | | | | — C — C — C = C — | | | | | | — C — C = C — C — | | | |

The final isomers will not have any double bonds and will belong to a third family of hydrocarbons called the cycloalkanes.They will have most of their carbon atoms joined by single bonds to form a ring. They are saturated hydrocarbonsOther carbon atoms could be branching off the ring.As a family, they are very similar to the alkanes and have similar uses : fuels, solvents etc.

H H \ / H C H \ /H —C C —H | | H —C C —H / \ H C H / \ H H

VideoRing

Molecules



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AlkanesC

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methane

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Smallest

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burn toproduceC

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onlysaturated

AlkenesC

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chains of carbon atoms

burn toproduceC

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Forming Alkenes Cracking allows the oil industry to change less useful, long chained alkanes into a more useful mixture of short chained alkanes and alkenes.

C10H22

C5H C2H C3H

It is not possible for all the smaller molecules produced to be alkanes. There are not enough hydrogen atoms available. At least one of the molecules will need to form a double bond, C = C, instead.

Burning Alkenes

alkeneburning

TubeA

TubeB

limewater

to pump

Just like any other hydrocarbon, alkenes are flammable and will react with oxygen to produce carbon dioxide and water.

The water can be trapped in a tube surrounded by ice (Tube A) while the carbon dioxide will turn lime water cloudy (Tube B)

butene + oxygen → carbon dioxid + watere

C H + → + H2O hexene + oxygen → carbon dioxid + watere

C H + → + H2O

VideoCrackingMolecular



Reaction with Bromine Alkanes decolourise bromine very slowly or not at allAlkenes decolourise bromineimmediately

Alkane molecules contain single carbon to carbon bonds, C C , and are good examples of saturated hydrocarbons

Alkene molecules contain a double carbon to carbon bonds, C C , and are good examples of unsaturated hydrocarbons

This makes the reaction with bromine very slow as one of the hydrogen atoms needs to be pulled off to allow a bromine atom to take its place.

This makes the reaction with bromine very fast as one of bonds in the double bond will break easily to allow both bromine atoms to join on.

sunlight

This very slow reaction is calledsubstitution

This very fast reaction is called

addition

VideoSaturated

Unsaturated

Saturated - single bonds onlyUnsaturated - multiple bond present (double or triple)



2.5 Introduction to Plastics

Making Perspex The monomer used to make perspex is a very runny liquid showing it is made up of small molecules.

An inhibitor is used to prevent the small molecules reacting with each other.An initiator is used to start the small molecules reacting to form much larger molecules called polymer. As the large molecules form, the liquid changes to solid. Perspex is unusual because it remains clear (transparent), hence its use in safety glasses.

Testing Properties

plastic appearance hardness flexibility density conductivity tested

polystyrene

polyamide (Nylon)

polyethene

polychloroethene (PVC)

polypropene

acrylonitrile butadiene styrene

Biopol

polyvinylalcohol (PVA)

Plastics have many different properties - which means they can be used in many different ways.

About the only property they all share is that they are very poor conductors of electricity - they are insulators.

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All about Plastics Plastics are substances which are flexle or able to be moulded into shape.(Think of plasticene).

Plastics are very large molecules called polymers, made by joining many small molecules together. The small molecules are called monomers.

There are some polymers made naturally by plants and animals. Examples of natural polymers include rubber - from rubber trees, cotton - from cotton bushes, hair (fur) - from mammals, wool - from sheep and silk - spun by silk worms.

Synthetic polymers are man-made - from the naphtha fraction in crude oil. These include:-polyethene - ‘plastic’ bagspolyprop - buckets etcnylonpolyester - shirts etcraypolychloroethene - footballs(PVC)

} Polymer Monomer Examples of uses

polythene ethene plastic bags, squeezy bottles washing up bowls

polypropene propene milk bottle crates, carpets, plastic ropes

polystyrene styrene plastic toys, expanded polystyrene as insulation and packaging

polyvinyl vinyl chloride guttering and pipes, electrical chloride (PVC) (chloroethene) insulation, floor & wall coverings

acrylic acrylonitrile fibre for clothing (wool substitute) (cyanoethene)

H H \ / C = C / \H HCH3 H \ / C = C / \H HC6H5 H \ / C = C / \H HCl H \ / C = C / \H HCN H \ / C = C / \H H



RS3 A

Some types of plastic can be heated ,melted and reshaped - these are called thermoplastics. This means that these plastics can be made by the chemical company, chopped into small pellets and sold to manufacturers who will melt the plastic when needed and pour it into moulds to form the shape they want.

As importantly, it means that objects made from a thermoplastic can be remelted and used to make new objects - they can be recycled.

The other type of plastic is called thermosetting - once formed, they cannot be melted and reshaped.

The plastics used to make electrical sockets, plugs, pan handles etc are examples of thermosets.

This means that the monomers have to be reacted toform the polymer inside the mould.

Plastics are so widely used nowadays partly because they are so resistant to decay.

This is fine until it comes time to dump these plastics.

‘Normal’ rubbish will rot away but most plastics will not.

More modern plastics are being developed which will rot when dumped because bacteria in the soil will be able to break the plastic down. These plastics are described as biodegradable.

There are several ways to tackle the problem of plastic waste: Re-u plastic objects such as . Rec the plastic whenever possible; only thermo are suitable.

Use more bio plastics. Use less plastics.

VideoPlastic

Pollution

VideoPlasticsTo Oil



Another problem with plastics and synthetic fibres is that many of them give off toxic fumes when they smoulder or burn.

The toxic fumes produced depend on the elements present in the plastic.

e.g. Carbon Monoxide ( CO ) by the incomplete combustion of carbon-containing plastics Hydrogen Chloride ( HCl ) from poly(chloroethene) (PVC) which contains chlorine Hydrogen Cyanide ( HCN) from polyurethane which contains nitrogen.

COHClHCN2.6 Addition Polymerisation

Making Polythene The monomer used to make polythene is the smallest alkene, ethene.

Ethene is an unsaturated hydrocarbon, and the double bond, C = C, makes it very reactive. The double bond can break open allowing new atoms or molecules to add on to the carbon atoms. When many many small molecules join together in this way it is called addition polymerisation.

Even with a reactive double bond, you need high pressures to force the ethenemolecules close together and a high temperature to help break the bonds open. A catalyst is also needed to help the reaction go faster.

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Addition polymers have a carbon backbone, and a 2 carbon repeating unit.



⇓ ⇑⇓ ⇓⇑

Topic Summary

Fuels and Combustion 1 • A fuel is a substance that releases a large amount of energy when it burns • An exothermic reaction is one in which heat energy is released • When a substance burns it reacts with oxygen • Combustion is another word for burning

Coal, oil and natural gas • Coal, oil and natural gas are fossil fuels, formed millions of years ago • A fossil fuel is one that has been formed from the remains of living things • Coal was formed from plant material, including trees • Oil and natural gas were formed from tiny sea creatures and plants

Fractional distillation • Oil requires a complex process of refining before it can be used • Crude oil is a mixture of carbon compounds, mainly hydrocarbons • Hydrocarbons are compounds containing carbon and hydrogen only • Fractional distillation is used to separate crude oil into fractions • A fraction is a group of compounds with similar boiling points

Fraction Boiling Range °C Carbon atoms End-uses

gas -160 to 20 1 to 4 fuel gases gasoline 20 to 65 5 to 6 petrol naphtha 65 to 180 6 to 11 petrochemicals kerosene 180 to 250 9 to 15 heating / jet fuel gas oils 250 to 350 15 to 25 diesel fuel residue > 350 > 25 bitumen, wax etc

• The fractions vary in viscosity (how ‘thick’) and flammability

Fraction Molecular Boiling Ease of Flammability Viscosity Size Point Evaporation

gas gasoline naphtha kerosene increasing increasing increasing increasing increasing gas oils residue



Explanation of Variations • Boiling range and viscosity increase as the molecular size increases because the forces of attraction between molecules are also increasing • Evaporation and flammability are also linked to molecular size. The smaller the molecules, the weaker the forces of attraction and easierto change liquid → gas.

Fuels and Combustion 2 • Many fuels contain carbon and hydrogen. When burned completely they produce carbon dioxide and water. • The test for carbon dioxide is that it turns lime water milky • The test for water is that it freezes at 0 °C and boils at 100 °C • Incomplete combustion of a carbon fuel can produce carbon (soot) and carbon monoxide • Carbon monoxide is a poisonous gas

Pollution problems • Burning fossil fuels produces carbon dioxide a ‘greenhouse gas’ that causes global warming • Sulphur in fuels (mainly coal) produce sulphur dioxide which causes acid rain (sulphur is removed from oil and gas during refining) • In petrol engines nitrogen and oxygen react to form poisonous oxides of nitrogen, including nitrogen dioxide • Special exhaust systems can convert pollutant gases into harmless gases • Using less fuel compared to air in car engines also reduces pollution • All new cars are fitted with catalytic convertors • These convert the oxides of nitrogen back into nitrogen • They change unburnt hydrocarbons and carbon monoxide into water and carbon dioxide



Alkanes • The alkanes are the main family of hydrocarbons found in natural gas / oil.

Name Molecular Formula Shortened Structural Formula

methane CH4 (g) CH4 ethane C2H6 (g) CH3CH3

propane C3H8 (g) CH3CH2CH3

butane C4H10 (g) CH3CH2CH2CH3

pentane C5H12 (l) CH3CH2CH2CH2CH3

hexane C6H14 (l) CH3CH2CH2CH2CH2CH3

heptane C7H16 (l) CH3CH2CH2CH2CH2CH2CH3

octane C8H18(l) CH3CH2CH2CH2CH2CH2CH2CH3

• The general formula for the alkanes is CnH2n + 2

• The simpler alkanes are mainly used as fuels • The alkanes burn to give carbon dioxide and water on complete combustion • The alkanes are said to be saturated because they contain only single C—C bonds • The alkanes cannot decolourise bromine water immediately on mixingAlkenes • The alkanes are another family of hydrocarbons but contain double C = C bonds


ethene C2H4 (g) CH2 = CH2

propene C3H6 (g) CH3CH = CH2

hexene C6H12 (l) CH3CH2CH2CH2CH = CH2

• The general formula for the alkenes is CnH2n

• The alkenes burn to give carbon dioxide and water on complete combustion • The alkenes are said to be unsaturated because they contain a double C = C bond • The presence of the C = C bond makes alkenes more reactive than alkanes • The alkenes can undergo many addition reactions eg.

CH2 = CH2 + H2 → CH3CH3

CH2 = CH2 + Br2 → CH2Br CH2Br • The alkenes can decolourise bromine water immediately on mixing • Decourising bromine water is a test for unsaturation



Cracking • Fractional distillation of crude oil gives more long-chained hydrocarbons (mainlyalkanes) than are needed by industry • Cracking is a method of producing smaller, more useful molecules by heating large hydrocarbon molecules in the presence of a catalyst • Cracking alkane molecules produces a mixture of alkanes and alkenes • There are not enough hydrogen atoms in an alkane molecule for it to produce only smaller alkanes on cracking • The presence of a catalyst, such as steel wool or aluminium oxide, allows cracking to take place at a lower temperature, making the process cheaper Cycloalkanes • The cycloalkanes are another family of hydrocarbons that contain single C—C bonds joined in rings


cyclopropane C3H6 (g)

cyclopentane C5H10 (l)

• The general formula for the cycloalkanes is CnH2n

• The cycloalkanes burn to give CO2 and H2O on complete combustion • The cycloalkanes are saturated because they contain a single C—C bonds • The cycloalkanes cannot decolourise bromine water immediately on mixing

Homologous series • The alkanes, alkenes and cycloalkanes are examples of homologous series • A homologous series is a group of compounds which: • can be represented by a general formula • have similar chemical properties • show a gradual change in physical properties, such as boiling points

Isomers • Isomers are compounds that have the same molecular formula but have different structural formulae

H H \ / H C H \ /H —C C —H | | H —C C —H / \ H C H / \ H H

H H H | | | H —C —C —C —H | | H H H C H | H

H H H H | | | |H —C —C —C —C —H | | | | H H H H



Plastics • Plastics and other synthetic fibres are examples of polymers - very large molecules formed by joining many small molecules called monomers • Monomers are the small molecules that join together to form a large polymer • Polymerisation is the process of making a polymer from many monomers • Most plastics and synthetic fibres are made from molecules found in crude oil • A synthetic fibre is one that is man-made e.g. nylon and terylene • A natural fibre is one that is found in nature e.g. wool, silk and cotton • Plastics are often used instead of traditional materials like wood, paper etc • The particular use is related to the properties of the plastic. • Most plastics have low density, are good heat and electrical insulators, and are water resistant

Plastics and Pollution • Very few plastics are biodegradable - they do not rot away • Natural materials such as wood, paper and cardboard are biodegradable • Plastics can release poisonous carbon monoxide if combustion is incomplete • Some plastics can also give off other toxic fumes when they burn or smoulder • The gases given off during burning or smouldering can be related to the elementsin the plastic carbon monoxide, CO when C present e.g polystyrene hydrogen chloride, HCl when Cl present e.g PVC hydrogen cyanide, HCN when N present e.g. polyurethane

Thermoplastics and Thermosetting plastics • A thermoplastic is one that softens on heating e.g. polythene, perspex etc • A thermosetting plastic does not soften on heating e.g. bakelite, formica etc • Only thermoplastics can be recycled

Making Polymers • Many polymers are made from the small unsaturated (C = C) molecules made by cracking • Many monomers made from ethene e.g chloroethene (vinyl chloride → PVC) • During the polymerisation of ethene, many ethene monomers join to make one large poly(ethene) molecule

H H

C C

H H

H H

C C

H H

H H

C C

H H

H H

C C

H H

H H

C C

H H

H H

C C

H H

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Petrochemicals Topic 2 - Chemistry Teaching Resources