alkanes alkenes and polymers

ALKANES, ALKENES and POLYMERS

ALKANES, ALKENES and POLYMERS

What are polymers and how do we make them?Why do some polymers soften when heated but others do not?

What are the benefits and drawbacks of the use of plastics?

Name____________________________

Class__________

Date__________

Teacher____________________________

CHEM - ADDITIONAL BOOKLET 6ALKANES, ALKENES and POLYMERSYou should:Tick

Be able to write structural formulae for simple alkanes (C1-C5) and ethene

Know the meaning of the terms saturated and unsaturated

Know how large saturated hydrocarbons (alkanes) can be cracked by heating in the presence of a catalyst to form smaller more useful hydrocarbon molecules including monomers (alkenes) for making polymers

Know the process of addition polymerisation of ethene to produce polythene and be able to write and interpret the following equation:

Be able to draw the repeating unit for the addition polymers, poly(ethene), poly(tetrafluoroethene) (PTFE) and polyvinyl chloride (PVC) in the form:

,

Relate the uses of polythene, PVC and PTFE to their properties

Relate the uses of thermoplastics and thermosets to their properties and structure

Use given data to compare the properties and uses of polymers and traditional materials

Evaluate the social, economic and environmental impact of the widespread use of plastic products, for individuals, communities and the environment

Alkanes and alkenesAlkanes are the simplest hydrocarbons in which carbon atom are joined to their neighbours by single bonds forming chains of carbon atoms which are further surrounded by hydrogens.

Alkanes are said to be SATURATED. This is because all carbon-carbon bonds are single, no more hydrogen atoms could possible fit onto the carbon chain.

The ALKANE series of hydrocarbons

Alkanes are a group of hydrocarbon molecules in which all the carbon and hydrogen atoms are only joined by single covalent bonds (eg C-H or C-C). Alkanes are known as saturated molecules because other atoms cannot add to them (compare with alkenes later on). The first four in the series are shown. They are not very reactive unless burned (SEE COMBUSTION OF HYDROCARBONS EARLIER (core)!

(1) is the molecular formula: a summary of the totals of each atoms of each element in one molecule; (2) is called the structural formula: it shows how all the atoms are linked with the covalent bonds -

(1), (3), methane

(main molecule in natural gas)

(1) (2) ethane

(1) (2) propane

(1) (2) butane

Pentane

Alkanes are not very reactive because their single carbon-carbon bonds make them very stable.ALKENESFor a hydrocarbon to be called an alkene it needs to contain at least one carbon-carbon double bond in its chain.

Alkenes are much more useful than alkanes because they are unstable. The fact that alkenes are unstable means that its easy to turn them into new substances.

Alkenes are unstable because of their double bonds. It is easy to combust alkenes in the same way as alkanes. Importantly alkenes can also undergo ADDITION reactions such as polymerisation.As more hydrogen could be added across a double bond, alkenes are said to be UNSATURATED.In the same way that ethane has two carbon atoms, so does ethene.

Catalytic Cracking

It is a fact that shorter chain hydrocarbons are more useful than longer chain hydrocarbons. Also; alkenes (hydrocarbons that contain at least one carbon=carbon double bond) are more useful than alkanes (saturated hydrocarbons with all single carbon-carbon bonds).

For these reasons, once distilled, long chain hydrocarbons undergo a process called CATALYTIC CRACKING.

Catalytic cracking occurs when long chain hydrocarbons are exposed to heat and a catalyst so that they break into smaller molecules. This type of reaction is a thermal decomposition reaction. During catalytic cracking alkenes are always produced as there are not enough hydrogen atoms to create two alkanes. Take for example the cracking of decane:

More about alkenes

The reason that alkenes are so useful is that they are unstable. The reason that they are unstable is that they contain double bonds (two shared pairs of electrons side by side which will repel one another). Because they are unstable alkenes readily undergo reactions called ADDITION reactions. One type of addition reaction occurs when alkenes add to each other many times to make long chain hydrocarbons known as POLYMERS. This is called POLYMERISATION.Polymerisation and polymers (plastics)This is where little alkenes such as ethene add together to make polymers. Polymers are plastics. We call the starting (reactant) alkenes monomers. The polymer in this case would be poly(ethene) commonly known as polythene. Here is a diagram to show the polymerisation of ethene:

There are an enormous number of different monomers that can be added together to make enormous numbers of polymers (plastics). Here are two more examples:

1. poly(tetrafluoroethene) (PTFE)

2. polyvinyl chloride (PVC)

Uses and properties of polymers

Starting monomerPolymerPolymer StructurePropertiesRelated uses

EthenePoly(ethene) Polythene

Good transparency

Chemically inert for example resistant to acids and alkalis.

Low density

FlexibleSandwich bags

Sandwich bags/ cling film

Squeeze bottlesWire/cable insulation

Vinyl chloridePoly(vinyl chloride) (PVC)

Shock absorbing

Chemically and heat resistant

Durable

Sound absorbingSoft car dashboards

Pipework

Cars - Cladding in door panels and undersealing.

Carpet underlay

Tetra fluoro ethenePoly(tetra fluoro ethane) (PTFE)

Non stick

Low friction

An excellent electrical insulator (dielectric)Saucepan coating

Used to coat armour piercing bullets to reduce wear on the firearm.

Circuit boards

Above are different examples of plastics (polymers). There are two types of plastic; thermoplastics and thermosetting plastics. Some of you may have talked about this in technology. There are two types of plastic which are classified according to the way in which they behave on heating.

ThermosetsThermoplastics

Made up of long hydrocarbon (polymer chains)


Chains separate on heating, plastic can be moulded into a new shape


On cooling crosslinks form, thermosets can never be remoulded into a new shape.

For this reason they are used as saucepan handles and electric light fittings.

On cooling no cross links form, the plastic can be remoulded again and again. For this reason they can be used for packaging and household containers.

Advantages and disadvantages of plasticsAdvantages there are a vast number of advantages of plastics, here are a small selection, see also the uses and properties of PVC etc above.1. Plastics are incredibly durable, they last a lot longer than many metals as they dont corrode.

2. Plastics are resistant to chemical attack

3. They are easy to mould into shape

4. They are easy to colour

5. There are an enormous number of different monomers therefore different plastics can be produced for different purposes. Disadvantages1. Most plastics are non-biodegradable.

2. During the combustion of many plastics, toxic fumes are released.

3. Plastics are costly to recycle

4. Plastics are made from fossil fuels which in the main are non-renewable.

End of Summary Sheets

Alkanes and Alkenes and Cracking6. Fill in the table below;

Name of hydrocarbonChemical formulaStructural formula

Methane

Ethane

Propane

Butane

Pentane

Decane

Ethene

2. Give the name of the only unsaturated molecule in the table. Explain why you have made your choice. _______________________________________________3. Why are alkenes generally more useful than alkanes?_________________________________________4. You only need to know the alkene ethene for your G.C.S.E but have a go at drawing the structures for propene, pentene and octene. (Before harassing your teacher straight away with this one try problem solving the prefix such as pent tells you the number of carbon atoms in the chain. Put the double bond between the first two carbons and remember, carbon must have four bonds around it when putting the hydrogens onto the chain. The general formula for an alkene is CNH2N.

7. Alkenes can be produced from long chain hydrocarbons during a process called catalytic cracking. Watch the video/DVD on catalytic cracking and answer the following:

Principles of Oil Refining part 2The first part of this video/DVD shows how crude oil is separated using fractional distillation.

Chemical Conversion what needs to happen to heavy residues produced during distillation.

______________________________________________________________________________________________

What is this process called? ________________________

What does it do?

______________________________________________________________________________________________

What is the most valuable product of thermal cracking?

_______________________________________________

What is thermal cracking not particularly good at? ______________________________________________________________________________________________

What is used to produce lighter fractions? ______________

What does a catalyst do? ___________________________

Write a sentence describing a prac used to show the action of a catalyst. For speed use symbols; Zinc=Zn, Sulphuric acid = H2SO4, Hydrogen = H2, Copper Sulphate = CuSO4.

_____________________________________________________________________________________________________________________________________________

What is the catalyst used in catalytic cracking?

_______________________________________________What happens to a catalyst at the end of a chemical reaction?

What is the main product formed in catalytic cracking? ______________________

Summary there are three different methods of cracking mentioned in this video. For your G.C.S.E you simply need to know that during cracking, heat and a catalyst are used to break up long chain H-Cs into shorter chains including alkenes.8. Here is an equation to show the cracking of decane into octane and ethane;

Draw two similar equations to show i. the cracking of octane to produce hexane and ethene ii. The cracking of decane to produce hexene and butane.

i.

ii.8. Carry out a quick prac to show the action of a copper sulphate catalyst on the reaction between zinc and sulphuric acid. Add 25 cm3 suphuric acid to a piece of zinc and add 5 cm3 copper sulphate solution. Write down your observations below:Before catalystAfter catalyst

Polymerisation(making plastics), different types of plastics and their advantages and disadvantages.1. Alkenes can be added together during reactions known as addition reactions to make polymers. Polymers are plastics.

2. Once polymers are formed; the way they arrange themselves on mass when heated dictates the type of plastic group they belong to; thermosetting or thermoplastics. Fill in the table using the summary sheet to help you:

ThermosetsThermoplastics





On cooling crosslinks form, thermosets can never be remoulded into a new shape.

For this reason they are used as _____________________________

_________________________

On cooling no cross links form, the plastic can be remoulded again and again. For this reason they can be used for ________________________________________________

3. Use this page to display the advantages and disadvantages of plastics. Draw a table, write a newspaper article, write an essay, draw a spider diagram, draw a whatever you like diagram, put down lots of points, approach this in any way you wish. BE CREATIVE!

This will test your listening skills

Write out the equation to show the polymerisation of ethene. Label the monomers and the polymer. Write about the uses and related properties of poly(ethene).

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I.C.T could do internet research here.

Draw the polymer PVC and write about its uses and related properties.

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Draw the polymer PTFE and write about its uses and related properties.

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Diagram

Diagram

Diagram

Diagram

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alkanes alkenes and polymers

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