A2 Support Pack Module 2 the Materials Revolution

26Salters Advanced Chemistry, Pearson Education Ltd 2009. University of York.

This document may have been altered from the original.

What you doWork in pairs or small groups so that you can discuss the task with other students.

You will be provided with a set of cards showing the names of some nylons and the structures of the monomers and repeating units of the polymers involved.1 Your task is to sort the cards into sets so that a name, structure(s) of the

monomer(s) and polymer repeating units all refer to the same nylon.2 When you have sorted out the cards, place them in lines to show:

nylon name monomer(s) structure(s) polymer repeating unit structure

3 Check with your teacher that you have correctly sorted out the cards. If not, think about how they might be rearranged.

4 Make a copy of the names and structures to use for revision.

A nylon is made from its monomers by condensation polymerisation. In this activity you will match together the names of nylons with the structures of their monomers and the repeating units of the polymers.

NamiNg NyloNs

mR2.1

setofcardsshowingnamesofnylons,structuresofmonomersandstructuresofpolymerrepeatingunits

Requirements

H2N(CH2)2NH2 H2N(CH2)6NH2

H2N(CH2)5NH2 H2N(CH2)10COOH

HOOC(CH2)2COOH ClOC(CH2)4COCl

HOOC(CH2)8COOH

(NH(CH2)2NHCO(CH2)2CO)



(NH(CH2)10CO)

Nylon-6,6

Nylon-2,4

Nylon-5,10

Nylon-11252_02-MR_SAC A2 SP.indd 26 17/3/09 08:27:51

27Salters Advanced Chemistry, Pearson Education Ltd 2009. University of York. This document may have been altered from the original.

Naming nylons mR2.1

H2N(CH2)2NH2 H2N(CH2)6NH2

H2N(CH2)5NH2 H2N(CH2)10COOH

HOOC(CH2)2COOH ClOC(CH2)4COCl

HOOC(CH2)8COOH




(NH(CH2)10CO)

Nylon-6,6

Nylon-2,4

Nylon-5,10

Nylon-11

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What you do1 Pour about 1 cm3 of the 1,6-diaminohexane solution into a 5 cm3 beaker.2 Carefully add an equal volume of the decanedioyl dichloride solution to the

beaker. Two separate layers will form. Do not mix them.3 Where the two layers are in contact, a nylon film forms. Use a pair of

tweezers to slowly pull out the nylon and hook the nylon thread onto a glass rod or a test tube.

4 Slowly wind the thread around the glass rod. As the nylon is removed, more forms at the solution interface, so you should be able to keep winding for some time.

5 Once you have made some nylon it needs to be washed thoroughly with tap water. Take care not to touch the nylon because it forms as a hollow tube, and there will still be some chemicals trapped in the middle of it.

A nylon is made from its monomers by condensation polymerisation. You may already have done this or a similar experiment in an earlier course. If so, you can omit this activity and go on to Activity MR2.3.

makiNg NyloN

mR2.2

accesstoafumecupboard5cm3 beakerglassrodortesttubetweezersprotectiveglovesdecanedioyldichloride,35%solutionincyclohexane(1cm3)1,6-diaminohexanesolution,35%aqueoussolution(1cm3)

CARE Decanedioyl dichloride has an irritating vapour that is a powerful lachrymator (eye irritant) and this effect is often delayed. Work in a fume cupboard or a well-ventilated laboratory.

Requirements

WEAR EYE PROTECTION

CaRE Eye protection (goggles) and gloves must

be worn.WEAR GLOVES

HARMFUL

decanedioyl chloride in cyclohexane solution

HIGHLY FLAMMABLE

Questions

1 What is the name of the nylon you have made? 2 Write out an equation to show the formation of this nylon.

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IntroductionIf you did Activity MR2.2 you will have made a nylon from its monomers by condensation polymerisation. A reaction like this, in which a new substance is made from simpler substances, is called a synthesis. The reverse process, in which a large molecule is broken down into simpler molecules, is called degradation. This type of reaction is often used by chemists to find out about the composition of substances. If they can identify the degradation products, they may be able to work out the structure of the original compound. The amide linkages in nylon can be hydrolysed (split by water) to give the parent di-acid and di-amine. The reaction with water is very slow indeed, but it can be speeded up by carrying out the hydrolysis in acid solution (acid hydrolysis). You will use moderately concentrated sulfuric(VI) acid (about 5.5 mol dm3) for the hydrolysis.

What you doPart 1: Breaking down the nylon

1 Place 2 g of nylon-6,6 granules into a 100 cm3 flask to which a reflux condenser can be attached.

2 Pour 35 cm3 of 5 mol dm3 sulfuric(VI) acid into the flask. (CARE Sulfuric acid of this concentration is very corrosive.) Fit the condenser to the flask (Figure 1).

3 Place the reaction flask and condenser in the heating mantle. Heat the reaction mixture under reflux for about 3 hours. (This technique is used when you want to heat reactants for some time, but not lose either the reactants or the products by evaporation.) Add a few anti-bumping granules (boiling chips) to help the mixture boil smoothly.

The nylon will all have dissolved after about 45 minutes, but you should carry on heating to complete the degradation.4 Allow the flask and contents to cool, place them in an ice bath and leave

overnight for crystals to form.5 Collect the crystals of hexanedioic acid by vacuum filtration. Keep the

filtrate for use later.

In this experiment you are going to convert some nylon-6,6 polymer back into its original di-acid and di-amine. The linkages in the nylon are broken down by hydrolysis using sulfuric acid. This activity will allow you to improve your skill in carrying out an organic reaction safely. You will learn how to purify an organic solid by recrystallisation and how to measure its melting point.

TakiNg NyloN apaRT

mR2.3

electricheatingmantlemelting-point apparatus for use up to 150 Cthin-walled capillary tubes (or melting-point tubes)apparatus for vacuum (suction) filtration100 cm3 boiling flask (e.g. round-bottomed flask)Liebig condenser250 cm3 conical flasks (2)100 cm3 measuring cylinder10 cm3 measuring cylinder250 cm3 beakers (2)watch glassanti-bumping granules (boiling chips)nylon-6,6 granules (2 g)sulfuric(VI) acid, approximately 5 mol dm3 (35 cm3)saturated sodium hydrogencarbonate solution (20 cm3)sodium hydroxide solution, 2 mol dm3 (5 cm3)iceuniversal indicator paper

CARE Sulfuric acid of this concentration is very corrosive.

Requirements

WEAR EYE PROTECTION

CaRE Eye protection (goggles) must be worn throughout.

sodium hydroxide solution

CORROSIVE

sulfuric(Vi) acid

CORROSIVE

&RQGHQVHU1\ORQJUDQXOHVVXOIXULF9,DFLG:DWHULQ :DWHURXW+($7Figure 1 Breaking down the nylon.

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mR2.3 Taking nylon apart

Part 2: Purifying the hexanedioic acid by recrystallisation

Your solid now needs to be purified by recrystallisation.

6 Place your hexanedioic acid crystals in a 250 cm3 conical flask. Add 10 cm3 of distilled water. Hold the neck of the flask with an insulating holder and gently heat the flask, swirling the contents at the same time. If some crystals remain when the water starts to boil, add a further 5 cm3 of water and reheat.

7 Carry on in this way until all the crystals have dissolved in the minimum quantity of water.

8 If your solution is clear, you can loosely cover the opening to the flask and leave the solution to cool overnight.

If the solution contains debris, this can be removed by carefully decanting most of the solution into a second flask, leaving the debris behind. You will need to reheat the solution to redissolve the crystals before covering it and leaving it to recrystallise.

9 Collect the crystals by vacuum filtration and leave them to dry on a watch glass. To speed things up you can place the watch glass in an oven or on a food-warming tray.

Part 3: Finding a melting point

Hexanedioic acid melts at 153 C. Find the melting point of your crystals and compare it with this value.

This is what you do to determine a melting point.

10 Carefullyheatoneendofasmallthin-walledcapillarytubeamelting-pointtubesothattheopeningisjustsealed.Leavethetubetocool.

11 Grind a small quantity of your dry crystals in one corner of the watch glass until you have a fine powder. Tap the open end of the melting-point tube into the fine powder so that a little powder packs into the tube. Invert the tube and tap it gently so that the powder falls to the closed end. Your teacher may show you an effective way of doing this. Do not try to put too much powder into the tube at once.

12 Repeattheprocedureuntilyouhaveabout0.51cmdepthofpowderinthetube. You may have an electrically heated melting-point apparatus that your teacher will show you how to use. Another type of melting point apparatus is shownbelowifyouareusingoneofthese,steps13 and 14 describe how to use it.*URRYHWRDOORZDLULQDQGRXWRIWKHDSSDUDWXV 7KHUPRPHWHU0HOWLQJSRLQWWXEH5XEEHUEDQG6XLWDEOHOLTXLG +($7

13 Fix the tube into position in the melting-point apparatus as shown in Figure 2.

14 Slowly heat the side-arm of the apparatus with a very low Bunsen burner flame. The design of the apparatus should ensure a circulation of warm liquid around the sample and thermometer. Watch the sample carefully. When it melts, the powder will collapse into a sticky liquid. Record the temperature at which this happens.

Figure 2 Melting-point apparatus.

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15 This will be a rough value for the melting point, because you were heating it quite quickly. To determine an accurate melting point, allow the apparatus tocooldowntoabout10Cbelowthevalueyouhavejustrecorded.Prepareanother sample while this is happening. Then repeat the process with the fresh sample and at a slower rate of heating.

16 Record the accurately determined melting point of your hexanedioic acid.

Part 4: Detecting the 1,6-diaminohexane produced

The diamine is still in solution in the filtrate obtained in Part 1, because it has formed a soluble salt by reacting with the sulfuric(VI) acid.

17 Take 5 cm3 of the filtrate and carefully pour it into 20 cm3 of saturated sodium hydrogencarbonate solution in a 250 cm3 beaker. (CARE Do not add the filtrate all in one go or the mixture will fizz dangerously.)

18 Use pH paper to make sure that the mixture is no longer acidic. If necessary add some more sodium hydrogencarbonate solution to achieve this.

19 Then add 5 cm3 of 2 mol dm3 sodium hydroxide solution to make the solution alkaline. Gently swirl the contents of the beaker and cautiously note the smell of the solution, which contains 1,6-diaminohexane. (For comparison, the trivial names of 1,4-diaminobutane and 1,5-diaminopentane are putrescine and cadavarine respectively, both of which are associated with the putrefaction of proteins in flesh.)

Taking nylon apart mR2.3

Questions

1 What property of hexanedioic acid is made use of in the recrystallisation process?

2 Explain why recrystallisation should produce a purer product.

3 Melting points are often used to identify compounds. They are also a good indication of the purity of a compound. Was your sample of hexanedioic acid pure? Explain your answer.

4 Write an equation for the hydrolysis of a short section of nylon-6,6 to produce hexanedioic acid and 1,6-diaminohexane.

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What you doA series of tests on butylamine, an example of an amine, are listed below. Before you start, read through all the tests and draw up a suitable table in which to record your observations.

Test 1: Solubilitya Add a few drops of butylamine to 1 cm depth of water in a test tube.b Test and record the pH of any solution that has been formed. Save the

mixture for the next test.

Test 2: Adding acid and alkalia Add a few drops of concentrated hydrochloric acid to the butylamine solution

from Test 1.b Make a note of any changes, including smell, before and after addition of the

acid.c Now add about 2 cm depth of 2 mol dm3 sodium hydroxide solution and

shake the tube gently; again, note any changes.

Test 3: Adding ethanoyl chloridea Place 10 drops of butylamine in a clean, dry test tube.b Add 10 drops, one drop at a time, of ethanoyl chloride (CARE Can react

violently) and make a note of your observations. Save your tube for the next test.

Test 4: Hydrolysing an amidea To the tube from Test 3, which contains a secondary amide, add 1 cm depth

of water and carefully stir the mixture.b Now add 3 cm depth of 2 mol dm3 sodium hydroxide solution.c Warm the mixture, and hold a piece of moistened pH paper at the mouth of

the test tube.

In this activity you will investigate the properties of the amine, butylamine.

iNVEsTigaTiNg aN amiNE

mR2.4

accesstoafumecupboardtesttubesandrackbutylamine(2cm3)concentratedhydrochloricacid(afewdrops)sodiumhydroxidesolution,2moldm3 (10 cm3)ethanoylchloride(2cm3)universalindicatorpaper

CARE Butylamine and ethanoyl chloride are volatile and have unpleasant, highly flammable vapours. Use the bottles in a fume cupboard and avoid inhaling the vapours.

Requirements

WEAR EYE PROTECTION

CaRE Eye protection must be worn.

concentrated hydrochloric acid

CORROSIVE

sodium hydroxide solution

CORROSIVE

CORROSIVE

butylamine

HIGHLY FLAMMABLE

CORROSIVE

ethanoyl chloride

HIGHLY FLAMMABLE

252_02-MR_SAC A2 SP.indd 32 17/3/09 08:27:53


Investigating an amine mR2.4

Questions

Test 1: solubility

1 Is butylamine soluble in water?

2 How can you explain any solubility in terms of bonding between particles?

3 Write an equation to explain any change to the pH of the water.

Test 2: adding acid and alkali

4 Write equation(s) for any changes you have noted.

Test 3: adding ethanoyl chloride

5 Write an equation for any reaction that occurs resulting in the formation of a secondary amide.

Test 4: Hydrolysing an amide

6 Write an equation for the reaction between the secondary amide and sodium hydroxide.

7 Explain any change to the pH paper in terms of the process occurring in the test tube.

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IntroductionLiquid crystals are sometimes referred to as the fourth state of matter, intermediate between the crystalline and liquid states. They are used to make LCD displays in many types of electronic equipment. The molecules making up liquid crystals have rod- or pencil-like structures. In this activity you will be condensing two molecules together to illustrate how a liquid crystal can be produced.

What you do1 Working in a fume cupboard, dissolve 1 g of cholesterol in 3 cm3 of pyridine

in a 50 cm3 conical flask.2 Add 0.4 cm3 of benzoyl chloride to the flask. (CARE Benzoyl chloride is a

lachrymator and will bring tears to your eyes.)3 Heat the mixture on a steam bath for 10 minutes. Allow the flask to cool.4 Add 15 cm3 of methanol to the mixture in the flask.5 Collect the solid cholesteryl benzoate by suction filtration using a Hirsch

funnel. Use a little methanol to rinse the flask and wash the crystals.6 To obtain high-quality crystals, recrystallise your crude product using about

15 cm3 of ethyl ethanoate in a boiling tube (cooling in an ice bath).7 Place your product on a watch glass and allow it to dry.8 Test the liquid crystal properties of your product by placing a small amount

of it (approx 0.1 g) on the end of a microscope slide. Hold the slide with tongs above a small Bunsen burner flame. Observe what happens when the compound is gently heated. Let the compound cool down and again note changes in the appearance of your sample.

In this activity you will make and test a compound that shows liquid crystal properties.

makiNg a liQuid CRysTal

mR2.5

accesstoafumecupboard250cm3 beaker50cm3 conical flaskapparatusforsettingupasteambathapparatusforvacuumfiltrationusingaHirschfunnelboilingtubestirringrodwatchglassmicroscopeslidetongscholesterol(1g)pyridine(3cm3)benzoylchloride(0.4cm3)ethylethanoate(15cm3)methanol(15cm3)crushedice

CARE Pyridine has a harmful vapour, benzoyl chloride is lachrymatory and methanol is toxic. Work in a fume cupboard and avoid inhaling any vapours. Wear eye protection at all times and disposable nitrile gloves when handling the chemicals.

CARE Pyridine, methanol and ethyl ethanoate are all highly flammable. Avoid naked flames.

Requirements

benzoyl chloride

CORROSIVE

WEAR EYE PROTECTION

CaRE Eye protection and protective gloves must be

worn.WEAR GLOVES

HARMFUL

pyridine

HIGHLY FLAMMABLE

ethyl ethanoate

HIGHLY FLAMMABLE

IRRITANT

methanol

HIGHLY FLAMMABLE

TOXIC

252_02-MR_SAC A2 SP.indd 34 17/3/09 08:27:54


Making a liquid crystal mR2.5

Questions

1 What changes in appearance of your product when it is heated and cooled suggest that it has liquid crystal properties?

2 The skeletal formula of cholesterol is shown opposite. Cholesterol undergoes a condensation reaction with benzoyl chloride to form the ester cholesteryl benzoate.

Draw out the skeletal formula of cholesteryl benzoate.

HO

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What you doStart by working on your own. Table 1 below includes simple amides and esters as well as polyamides (nylons) and polyesters.

1 For each of the starting materials shown in Table 1, work out the structure(s) of the product(s) formed when the ester or amide is hydrolysed under the conditions indicated.

2 Now compare your answers with those of another student. Discuss your answers and add to, or modify, your tables where necessary and then compare your answers with those agreed by another pair of students. Amend your answers where necessary.

3 Finally, check with your teacher that your answers are correct. Make a note of any structures that you were less confident about working out, to help you when you come to revise this topic at a later date.

Table 1

amide or ester Reagent Hydrolysis product(s)

CH3CONH2 HCl

C2H5CONH2 NaOH

CH3COOC2H5 HCl

HCOOCH3 NaOH

( NH(CH2)6NHOC(CH2)4CO ) HCl

( NH(CH2)5NHOC(CH2)8CO ) NaOH

( OCH2CH2OOCC6H4CO ) HCl

( O(CH2)3OOCCO ) NaOH

( NH(CH2)5CO ) HCl

( OCH2CH2CO ) NaOH

Amides and esters can be hydrolysed using acid or alkali. This activity will help you check that you understand how the products of hydrolysis depend on the conditions used.

HydRolysiNg amidEs aNd EsTERs

mR2.6

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What you doWork with one or two other students for this activity so that you can discuss your ideas.

You will be provided with a set of cards giving information about various aspects of the manufacture and disposal of disposable cups made from paper and from polystyrene.

1 Use the information on the cards to help you answer the questions that follow. You may find it useful to design a table in which to summarise the information about paper and polystyrene cups.

This activity gives you an opportunity to compare the impact on the environment of the manufacture and disposal of paper and plastic disposable cups.

papER oR plasTiC? WHiCH is

bETTER FoR THE ENViRoNmENT?

mR3

setofinformationcards

Requirements

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3

5

7

9

2

4

6

8

10

11

13

15

17

12

14

16

The main raw material needed to make paper is wood, which is a renewable resource.

However, collecting wood impacts on the landscape trees have to be cut down both for use as wood and to make space for roads so that the wood can be transported.

4.1 g of petroleum is needed to make a paper cup. 3.2 g of petroleum is needed to make a polystyrene cup.A paper cup weighs about 10.1 g.A polystyrene cup weighs about 1.5 g.A paper cup costs about 5p;a polystyrene one costs about 2p.

Paper cups are made from bleached wood pulp, which is made from wood chips. Only about half of the chips are turned into pulp. Bark and some wood waste are burned to supply energy for the process.In total, about 33 g of wood and bark are used per paper cup.

To make a paper cup, chemicals such as chlorine, sodium hydroxide, bleach, sulfuric(VI) acid, sulfur and limestone are needed. These chemicals are not recycled. In total, about 1.8 g of these chemicals are needed per cup produced.

More petroleum is needed to make a paper cup than a polystyrene one. The wood for paper cups has to be transported by road or rail to the manufacturing plant.If the cup has a wax or plastic coating, even greater amounts of petroleum are needed per cup.

Efficient catalysts are used to make polystyrene, so most of the chemicals involved (other than those from oil) can be recycled.Of these additional chemicals all but around 0.05 g per cup are reused in the process.

So much wood pulp is used to make a paper cup that the whole process requires about:12 as much steam,36 as much electricity and2 as much cooling wateras the process used to make a polystyrene cup.

A polystyrene cup is made from oil. Collecting and transporting oil can cause environmental damage, particularly if spills occur during drilling or transportation.The oil (or natural gas) needed to produce polystyrene cups is taken by pipeline to the manufacturing plant.

Making polystyrene produces about 20 kg of waste metal salts per tonne of polystyrene produced.Making paper produces about 120 kg of waste metals per tonne of paper produced (depending on the type of paper plant).

It is possible to reuse polystyrene cups because they do not soak up water.Paper cups could be reused but washing would destroy them.

Paper cups cannot be recycled. The glues that hold parts of the cup together cannot be removed in the recycling process.Plastic-coated paper is even more difficult to recycle.

In a landfill site, paper can biodegrade anaerobically to produce methane and carbon dioxide in a 2:1 ratio. Paper may biodegrade very slowly, especially in dry regions of the world. Polystyrene does not biodegrade.Methane has about 10 the greenhouse effect of carbon dioxide.

About 580 as much waste water is produced to make a paper cup compared to making a polystyrene cup.The waste chemicals are mainly removed from the water but there is still at least 10 more chemical waste for paper cups than for polystyrene ones.

More waste gas is produced for polystyrene than for paper (per tonne of material made).Paper cups are heavier than polystyrene ones, so less waste gas is produced per polystyrene cup

Polystyrene cups can be recycled. The recycled material cannot be used for food or drink containers, but can be made into packaging, insulation, patio furniture, tiles and other products.Only a small proportion of polystyrene waste is actually recycled at present.

Both paper and polystyrene can be incinerated and the energy produced can be used.Paper provides 20 MJ/kg and polystyrene produces 40 MJ/kg.Carbon dioxide is produced in the process.

For the same number of cups, 1 tonne of landfill waste will be generated if the cups are made from polystyrene and 6 tonnes if the cups are made from paper.

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mR3 Paper or plastic? Which is better for the environment?

1

3

5

7

9

2

4

6

8

10

11

13

15

17

12

14

16

The main raw material needed to make paper is wood, which is a renewable resource.

However, collecting wood impacts on the landscape trees have to be cut down both for use as wood and to make space for roads so that the wood can be transported.

4.1 g of petroleum is needed to make a paper cup. 3.2 g of petroleum is needed to make a polystyrene cup.A paper cup weighs about 10.1 g.A polystyrene cup weighs about 1.5 g.A paper cup costs about 5p;a polystyrene one costs about 2p.

Paper cups are made from bleached wood pulp, which is made from wood chips. Only about half of the chips are turned into pulp. Bark and some wood waste are burned to supply energy for the process.In total, about 33 g of wood and bark are used per paper cup.

To make a paper cup, chemicals such as chlorine, sodium hydroxide, bleach, sulfuric(VI) acid, sulfur and limestone are needed. These chemicals are not recycled. In total, about 1.8 g of these chemicals are needed per cup produced.

More petroleum is needed to make a paper cup than a polystyrene one. The wood for paper cups has to be transported by road or rail to the manufacturing plant.If the cup has a wax or plastic coating, even greater amounts of petroleum are needed per cup.

Efficient catalysts are used to make polystyrene, so most of the chemicals involved (other than those from oil) can be recycled.Of these additional chemicals all but around 0.05 g per cup are reused in the process.

So much wood pulp is used to make a paper cup that the whole process requires about:12 as much steam,36 as much electricity and2 as much cooling wateras the process used to make a polystyrene cup.

A polystyrene cup is made from oil. Collecting and transporting oil can cause environmental damage, particularly if spills occur during drilling or transportation.The oil (or natural gas) needed to produce polystyrene cups is taken by pipeline to the manufacturing plant.

Making polystyrene produces about 20 kg of waste metal salts per tonne of polystyrene produced.Making paper produces about 120 kg of waste metals per tonne of paper produced (depending on the type of paper plant).

It is possible to reuse polystyrene cups because they do not soak up water.Paper cups could be reused but washing would destroy them.

Paper cups cannot be recycled. The glues that hold parts of the cup together cannot be removed in the recycling process.Plastic-coated paper is even more difficult to recycle.

In a landfill site, paper can biodegrade anaerobically to produce methane and carbon dioxide in a 2:1 ratio. Paper may biodegrade very slowly, especially in dry regions of the world. Polystyrene does not biodegrade.Methane has about 10 the greenhouse effect of carbon dioxide.

About 580 as much waste water is produced to make a paper cup compared to making a polystyrene cup.The waste chemicals are mainly removed from the water but there is still at least 10 more chemical waste for paper cups than for polystyrene ones.

More waste gas is produced for polystyrene than for paper (per tonne of material made).Paper cups are heavier than polystyrene ones, so less waste gas is produced per polystyrene cup

Polystyrene cups can be recycled. The recycled material cannot be used for food or drink containers, but can be made into packaging, insulation, patio furniture, tiles and other products.Only a small proportion of polystyrene waste is actually recycled at present.

Both paper and polystyrene can be incinerated and the energy produced can be used.Paper provides 20 MJ/kg and polystyrene produces 40 MJ/kg.Carbon dioxide is produced in the process.

For the same number of cups, 1 tonne of landfill waste will be generated if the cups are made from polystyrene and 6 tonnes if the cups are made from paper.

Questions

1 What are the advantages of disposable cups over traditional cups?

2 What are the main advantages to the environment of using paper to make disposable cups?

3 What are the main advantages to the environment of using polystyrene to make disposable cups?

4 Which do you think are better for the environment paper or polystyrene disposable cups? Explain your answer.

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What you do1 Start by chewing a piece of bubble gum until all the taste has gone.2 Gently pull the gum and then release it.3 Now pull the gum so that it stretches to about eight times its original length

and then release it.4 Shape your piece of bubble gum into a flat disc about 2.5 cm across. Wrap it

in some plastic film and place it in the freezer for about 15 minutes.5 Take the gum out of the freezer. Observe what happens when you try to

quickly bend the gum. Allow the gum to return to room temperature and then try to bend it again.

6 Dispose of your gum in a responsible way.

The polymer in bubble gum can be elastic or glassy, depending on temperature. You can study both forms with the help of a domestic freezer.

bubblE gum oR bubblE glass?

mR4.1

bubblegumfreezer

CARE Do this experiment at home, not at school or college.

CARE Wash your hands before and after handling your own bubble gum. Do not handle other peoples gum.

Requirements

Questions

1 a Does the gum show any elastic properties when it is gently stretched?

b When the gum is further stretched does it still show elastic properties and does it completely return to its original length?

c What term is used to describe this irreversible change?

2 a What happens when you try to bend the gum after it has been in the freezer?

b Can you explain the result? c What happens as the gum returns to room temperature?

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What you do1 Cook some spaghetti, in a saucepan or large beaker, using the manufacturers

instructions for the amount of water and length of time.2 When cooked, strain the spaghetti so that it is free of water and pour it into a

transparent container.3 Allow the spaghetti to cool then turn out the solid cake of spaghetti onto a

flat surface (e.g. a plate).4 Sketch the arrangement of spaghetti strands on the base of the solid cake.5 The spaghetti acts as a model for the chains in a polymer and the way they

pack together in solid materials. On your diagram, label the areas where: a the arrangement resembles a crystalline structure b the arrangement resembles an amorphous structure.

In this activity, you will use strands of spaghetti to model how the molecules of some polymers are aligned in a solid.

usiNg spagHETTi To modEl polymER

sTRuCTuRE

mR4.2

spaghetti(about250g)2dm3 beaker (or saucepan)Bunsenburner,tripodandgauze(orkitchenhob)transparentcontainerwithaflatbaseandstraightsides(suchasaplasticicecreamorsandwichbox)plateorotherflatsurfacestrainer(sieveorcolander)

CARE Do not eat any spaghetti cooked in the laboratory.

Requirements

252_02-MR_SAC A2 SP.indd 40 17/3/09 08:27:55


IntroductionThe checklist below covers the key points in Chemical Storylines MR1 to MR5. The statements listed correspond to learning outcomes in the specifications for the A2 examinations. Remember that you will come back to many of these ideas in later modules. You will probably have made summary notes of the main ideas that you have met. Now is a good time to make sure that your notes cover all the points you need. If you feel that you are not yet able to meet the requirements of all the statements in the list, you should look again at the areas concerned, seek help from your teacher if necessary and develop your notes accordingly. Most of the points are covered in Chemical Ideas, with supporting information in Chemical Storylines or the activities. However, if the main source of information is in a storyline or an activity, this is indicated.

What you doRead and think about each of the statements in the checklist. Put a tick in the column that best represents your current ability to do what is described.A I am confident that I can do thisB I need help to clarify my ideas on thisC I am not yet able to do thisYou will be sharing this information with your teacher so that you can work together to improve your understanding.

at the end of Chemical storylines mR1 to mR5 you should be able to: a b C

explainandpredicttheeffectoftemperature,crystallinityandchainlengthonthepropertiesofpolymers: temperature:intermolecularbondshavemoreeffectasthetemperatureislowered;apolymersoftensabove

its Tm and becomes brittle below its Tg activity mR4.1

crystallinity (regularpackingofthechains,duetotheregularstructureofthepolymer):thechainsarecloserand the intermolecular bonds have more effect, leading to greater strength activity mR4.2

chain length:withlongerchainstherearemoreintermolecularbonds,leadingtogreaterstrength,andflexibility depends on the ability of the polymer chains to slide over each other

explainthefollowingwaysthatchemistscanmodifythepropertiesofapolymertomeetparticularneeds: cold-drawing to make the structure more crystalline copolymerisation use of plasticisers

understandthatthepropertiesofallmaterialsdependontheirstructureandbondingandexplainexamplesgiven relevant information Chemical storylines mR2, mR3, mR4

recognisemembersofthefollowinghomologousseries:aminesandamides

usesystematicnomenclaturetonameandinterpretthenamesofaliphaticprimaryaminesanddiamines(use the prefix amino- for the NH2 group together with the parent hydrocarbon, e.g. 2-aminopropane, 1,6-diaminohexane)

explainthedifferencebetweenadditionandcondensationpolymerisation

predictthestructuralformulaofthecondensationpolymerformedfromgivenmonomer(s),andviceversa

describethehydrolysisofestersandamidesbybothaqueousacidsandalkalis,includingsaltformationwhere appropriate activity mR2.6

describethefollowingreactionsofamines: neutralisation by acids acylation to form an amide

This activity helps you check your knowledge and understanding of the new topics that you have covered in this module.

CHECk youR kNoWlEdgE aNd uNdERsTaNdiNg

mR5

continued

252_02-MR_SAC A2 SP.indd 41 17/3/09 08:27:55



recalltheprocedureforpurifyinganorganicsolidproductbyrecrystallisation,andexplainthatthesolventused:

must be one in which the substance is very soluble at higher temperatures and insoluble, or nearly so, at lower temperatures

is saturated by the substance at higher temperatures. On cooling the saturated solution, the substance then crystallises out to leave the impurities in solution activity mR2.3

explainthebasicnatureoftheaminogroup,intermsofalonepaironthenitrogenacceptingaprotontogivea cation

understandhowtheprinciplesofgreenchemistryareimportantinthemanufacture,use,recyclingandtheeventualdisposalofpolymers,including:

minimising any hazardous waste during production of raw materials and their resulting polymers to reduce any negative impact on the environment

reducing carbon emissions resulting from the life cycle of a polymer recycling to produce energy and chemical feedstocks

synoptic statements

The following statements describe the knowledge and understanding that you have covered in more detail in earlier modules, but that you have met or used again when studying The materials Revolution.

Check that you are confident about these learning outcomes they may be assessed in the A2 examinations in questions that require you to apply your knowledge and understanding from different areas of the subject.

a b C

explainthetermelectronegativity recallqualitativelytheelectronegativitytrendsinthePeriodicTable Chemical ideas 3.1

userelativeelectronegativityvaluestopredictbondpolarityinacovalentbond decidewhetheramoleculeispolarornon-polarfromitsshapeandthepolarityofitsbonds

Chemical ideas 5.3

explain,giveexamplesofandrecogniseingivenexamplesthefollowingtypesofintermolecularbond: instantaneous dipoleinduced dipole bonds (including dependence on branching and chain length of

organic molecules) permanent dipolepermanent dipole bonds, hydrogen bonds Chemical ideas 5.3, 5.4

mR5 Check your knowledge and understanding

252_02-MR_SAC A2 SP.indd 42 17/3/09 08:27:55


End of module test mR

The Materials Revolution end of module test 60 marks (1 hour)1 Nylon was invented in 1935 by Wallace Carothers. His invention resulted from a planned research project in which he was trying

to make a polymer in which the molecular chains were built up in a similar way to the protein chains in silk.

He allowed pairs of compounds (e.g. compound a and compound b) to react together under suitable conditions.

H2N(CH2)6NH2 HOOC(CH2)4COOH

Compound a Compound b

a i To which homologous series does compound a belong? [1] ii Give the systematic name for compound a. [1] iii Show the ions formed when compound a reacts with hydrochloric acid and explain the mechanism by which the amine

group acts as a base. [3]

b i Draw a skeletal formula for the repeating unit in the resulting nylon, showing one unit of a linked to one unit of b. [2] ii Nylon is a condensation polymer. Explain the meaning of the terms condensation and polymer. [2] iii Give one difference between the formation of a condensation polymer and that of an addition polymer. [1]

c The same nylon can be made by reacting compound a with compound C, ClOC(CH2)4COCl. i Name the functional group in compound C. [1] ii Apart from the nylon, what other product forms when compound a reacts with compound C? [1] iii Choose from the following list the term that best describes the reaction of compound a with compound C. [1]

acylation addition esterification hydrolysis redox

iv Suggest two reasons why industrial companies do not use compound C to make nylon on a large scale. [2]

d Samples of nylon and high-density poly(ethene) (hdpe) are compared. They have the same average polymer chain lengths. i Suggest why the chain lengths are kept the same for the comparison. [1] ii Name the type of intermolecular bond present in hdpe. [1] iii Name the strongest type of intermolecular bond present in nylon and draw a diagram to show how one of these bonds

forms between two adjacent chains. Show lone pairs and partial charges where appropriate. [5] iv The nylon has a higher Tg than the hdpe. Explain the meaning of Tg and explain why the nylon has a higher Tg. [4] [ToTal: 26 maRks] (OCR Chemistry B (Salters) question, adapted for the 2008 specification)

2 Polyesters are widely used as fibres, films and packaging materials. The repeating unit of the most common polyester, Terylene, is shown below. 7HU\OHQHCOOO CH2CH2 COa This polyester is hydrolysed using sodium hydroxide. Draw the structures of the organic molecule and the organic ion that are

formed. [2]

b i Name the strongest type of intermolecular bond between the polyester chains. [1] ii Draw a diagram of two sections of adjacent polyester chains, and show how these intermolecular bonds arise. [2]

c Terylene can be cold-drawn. i Explain how cold-drawing is carried out. [1] ii What is meant by crystallinity and what is the effect of cold-drawing on the structure of a polymer? [2] iii State one property of Terylene that would be affected by cold-drawing. Describe how this property would change and

explain the difference in terms of changes in structure. [3]

d Name two other methods by which a polymers properties can be modified. [2]

e i Suggest two methods of disposing of objects made from polyesters. [2] ii Give two reasons why the recycling of plastics is a good idea. [2] [ToTal: 17 maRks] (OCR Chemistry B (Salters) question, adapted for the 2008 specification)

252_02-MR_SAC A2 SP.indd 43 17/3/09 08:27:55



mR End of module test

3 The polymer Kevlar is used to make bullet-proof vests and the cords that reinforce the walls of car tyres. The diagram below shows the structure of the repeating unit in Kevlar. .HYODUOC NHCONHa i Kevlar is a condensation polymer. Draw the structures of the two monomers from which it is made. [2]

ii What name is given to the CONH group? [1]

b i What reagents and conditions would you use to hydrolyse Kevlar into its monomers in the laboratory? [2] ii One of the hydrolysis products is a white crystalline solid. Describe how you would obtain a pure sample of this product

by recrystallisation using water as the solvent. [5] iii Give two important features of the solvent used for recrystallisation. [2] iv How would you show that the sample you had obtained was pure? [2]

c Kevlar is very useful because it has a high tensile strength, it is fire-resistant and it is low-density. Explain each of these properties in terms of the structure of Kevlar. [3]

[ToTal: 17 maRks] (OCR Chemistry B (Salters) question, adapted for the 2008 specification)

252_02-MR_SAC A2 SP.indd 44 17/3/09 08:27:55



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252_12_SAC A2_TT MR.indd 234 17/3/09 08:32:19


MRTHE MATERIALS REVOLUTION

Concept mapThis concept map shows how the major chemical ideas in this teaching module develop throughout the course.

Concept First introduced in module

Developed in module(s)

Assumed in module(s)

Relative atomic mass and relative formula mass EL all

Amount of substance EL DF all

Chemical formulae and inorganic nomenclature EL ES all

Balanced chemical equations EL DF all

Atomic structure EL all

Covalent bonding EL DF, ES, PR all

Relationship between properties, and bonding and structure

EL MR, TL, AI, CD, O DF, ES, PR, SS

The Periodic Table EL ES, SS, AI several

Catalysis DF A, TL, SS, AI several

Homologous series DF PR several

Nomenclature of organic compounds DF ES, PR, WM, MR, TL, CD

MD

Structural formulae (full, shortened and skeletal) DF ES, PR all organic modules

Organic functional groups DF ES, PR, WM, MR, TL, CD

MD

Properties of alkanes DF several

Alkenes DF PR WM, MR, CD, MD

Structure of benzene DF CD WM, MR, TL, MD

Alcohols and ethers DF PR, WM, MR ES, CD, MD

Ionic equations ES SS several

Electronegativity and bond polarity ES PR, O several

Intermolecular bonds ES PR, MR, TL, O AI, CD, MD

Reaction mechanisms ES A, PR, MR, TL, CD MD

Industrial applications ES WM, MR, TL, SS, AI

MD

Bond fission A PR several

Elimination reactions PR several

Carboxylic acids PR WM, MR TL, AI, CD, MD

Polymers and polymerisation PR MR, TL MD

Esters WM MR AI, CD, MD

Condensation reactions WM MR, TL MD

Acyl (acid) chlorides WM MR CD, MD

Delocalisation of electrons WM CD several

Amines MR TL CD, MD

Amides MR TL CD, MD

Acylation MR CD, MD

Green chemistry MR TL, AI CD, MD

252_12_SAC A2_TT MR.indd 235 17/3/09 08:32:19



MR2.1 Naming nylons

This activity provides students with an opportunity to check their ability to name nylons and to write out structures for monomers and polymer repeating units. It is designed to complement Assignment 1 in the Chemical Storylines book and questions in Chemical Ideas. Through discussion students are able to identify the aspects that they feel confident with and those they are less certain about and may require help to clarify. Some teachers may wish to laminate the cards before use.

Nylon 2,4 H2N(CH2)2NH2 HOOC(CH2)2COOH (NH(CH2)2NHCO(CH2)2CO)Nylon 6,6 H2N(CH2)6NH2 ClOC(CH2)4COCl (NH(CH2)6NHCO(CH2)4CO)Nylon 5,10 H2N(CH2)5NH2 HOOC(CH2)8COOH (NH(CH2)5NHCO(CH2)8CO)Nylon 11 H2N(CH2)10COOH (NH(CH2)10CO)

MR Advance warning

Activities: notes and answers to questions

Storyline: answers to assignments 1 a i Nylon-6,8 ii Nylon-9,9 iii Nylon-4,4 b i CO(CH2)5NH, nylon-6 ii NH(CH2)5NHCO(CH2)5CO, nylon-5,7 c i H2N(CH2)5NH2 and ClCO(CH2)8COCl ii HCl iii NH(CH2)5NHCO(CH2)8CO2 a

CO

OH C O HO

H O CH

H

C OH

H

H

b Permanent dipolepermanent dipole bonds and instantaneous dipoleinduced dipole bonds.

3 Poly(ethenol) dissolves in aqueous solutions; polyester made from lactic acid hydrolyses. A more precise rate of polymer dissolution can be obtained from the latter. Also, the product of hydrolysis of the lactic acid-based polyester occurs naturally in the body.

4 a

C NH

O

ONH

C

b

N

H H

N

C CO

O OO

H

H

H

H

c The NH groups in Kevlar become protonated and the interchain hydrogen bonding is disrupted.

d Protons are transferred from the polymer to the water. The hydrogen bonding in Kevlar is re-established.

Activity Item(s) Essential/optional Typical quantity per activity

MR2.1 Sets of cards Essential 1 per pair of students

MR2.2 5% decanedioyl dichloride in cyclohexane5% 1,6-diaminohexane in aqueous solution5 cm3 beaker

Essential 1 cm3 of each liquid,1 beaker

MR2.3 Nylon-6,6 granulesHeating mantle

EssentialOptional (but recommended)

2 g1

MR2.5 CholesterolBenzoyl chloride50 cm3 conical flask

Essential 1 g cholesterol,0.4 cm3 benzoyl chloride1 flask

MR4.1 Bubble gum, e.g. Hubba Bubba Essential 1 piece

MR4.2 Spaghetti Essential 250 g

Advance warningThe following items needed for activities in this module may not be in your school currently, and might take a little time to obtain.

252_12_SAC A2_TT MR.indd 236 17/3/09 08:32:20

Activities: notes and answers to questions MR


MR2.2 Making nylon

Safety note Information about hazardous chemicals is given on the activity sheet. Decanedioyl dichloride is corrosive and toxic and is a powerful irritant to the eyes. It should be handled in a fume cupboard.Some students will have already done this activity in earlier studies. It is not intended that they should repeat the experiment.1 Nylon-6,102 nH2N(CH2)6NH2 + nClOC(CH2)8COCl

(HN(CH2)6NHCO(CH2)8CO)n + 2nHCl

MR2.3 Taking nylon apart

Safety note Information about hazardous chemicals is given on the activity sheet. The liquid throughout this experiment contains approximately 5 mol dm3 sulfuric(VI) acid, which is very corrosive. Students should take care when handling the mixture, particularly when performing the vacuum filtration and adding the solution to sodium hydrogencarbonate. Many teachers have preferred to perform Part 1 of this activity as a demonstration, and to use double quantities and a 250 cm3 flask. Students can then take samples of impure crystals and work with them from Part 2 onwards. The nylon-6,6 granules should have disappeared after about 1 hour, but the mixture should be refluxed for at least 21/23 hours for hydrolysis to be completed. If you do not have an electric or gas-heated melting point apparatus, the setup in Figure 2 in the activity offers a low-cost alternative. A suitable liquid to use would be medicinal paraffin or dibutylphthalate. The melting point of pure hexanedioic acid is 153154 C.1 It is more soluble in hot water than in cold.2 The impurities remain dissolved in the solvent as the

hexanedioic acid crystallises.3 The presence of impurities lowers the melting point. The

substance no longer melts sharply, but over a range.4 HN(CH2)6NHCO(CH2)4CO + H2O

H2N(CH2)6NH2 + HOOC(CH2)4COOH

MR2.4 Investigating an amine

Safety note Information about hazardous chemicals is given on the activity sheet.

As preparation for this activity, it may help to ask students to think about how ammonia would behave in the four tests.1 Butylamine is soluble in water.2 Butylamine forms hydrogen bonds to water molecules.3 Butylamine solution is alkaline because of the reaction C4H9NH2 + H2O C4H9NH3+ + OH4 The smell of the amine is lost on addition of acid because

the free amine is removed by the reaction C4H9NH2 + H3O+ C4H9NH3+ + H2O The amine is regenerated on addition of alkali C4H9NH3+ + OH C4H9NH2 + H2O5 Vigorous effervescence. HCl is given off and a colourless

solid is produced. C4H9NH2 + CH3COCl C4H9NHCOCH3 + HCl6 Sodium hydroxide solution hydrolyses the amide to

produce butylamine. C4H9NHCOCH3 + OH C4H9NH2 + CH3COO7 The moistened pH paper turns blue because of the

reaction of butylamine with water (see 3).

MR2.5 Making a liquid crystal

Safety note Information about hazardous chemicals is given on the activity sheet. The safety precautions described must be strictly adhered to.1 As the cholesteryl benzoate is heated gently the solid

moves through a cloudy liquid phase before it goes clear. This illustrates it passing through a liquid crystal phase. On cooling, the liquid goes cloudy before solidifying.

2

O

O

MR2.6 Hydrolysing amides and esters

This activity helps students to check that they understand how the products of hydrolysis of amides and esters depend on the conditions used to bring this about. By comparing their answers with those of other students they can identify aspects that they feel confident with and those they are less certain about and may require help to clarify.

Amide or ester Reagent Hydrolysis products

CH3CONH2 HCl CH3CONH3+ Cl

C2H5CONH2 NaOH C2H5COO Na+ + NH3

CH3COOC2H5 HCl CH3COOH + C2H5OH

HCOOCH3 NaOH HCOO Na+ + CH3OH

(NH(CH2)6NHOC(CH2)4CO ) HCl Cl +H3N(CH2)6NH3

+ Cl + HOOC(CH2)4COOH

(NH(CH2)5NHOC(CH2)8CO ) NaOH H2N(CH2)5NH2 + Na+ OOC(CH2)8COO

Na+

(OCH2CH2OOCC6H4CO ) HCl HOCH2CH2OH + HOOCC6H4COOH

(O(CH2)3OOCCO ) NaOH HO(CH2)3OH + Na+ OOCCOONa+

(NH(CH2)5CO ) HCl Cl +H3N(CH2)5COOH

(OCH2CH2CO ) NaOH HOCH2CH2COO Na+

252_12_SAC A2_TT MR.indd 237 17/3/09 08:32:20

MR Activities: notes and answers to questions



MR3 Paper or plastic? Which is better for the environment?

Each group of students will need one set of cards, which could be cut out and laminated before the lesson. The aim of this activity is to encourage students to consider the whole life cycle of an object, including manufacture and disposal, while assessing the impact on the environment of making and using that object. Teachers may like to get their students to discuss which of paper or polystyrene cups they would opt for (and why) before handing out the information cards. A suggested table for summarising the information is given below.1 Consumers might want a disposable cup because they

want to take their drink away from the place they have bought it. Some people prefer disposable cups because they think that they are more hygienic.

2 Paper cups have the advantages of being biodegradable (although this has a greater greenhouse gas impact than burning them) and produce smaller amounts of metal salts in the manufacturing process.

3 Polystyrene cups use smaller amounts of raw materials and the manufacturing process produces less waste than the paper cup manufacturing process. Polystyrene cups are lighter and so lead to less impact due to transport. Polystyrene cups can also be re-used and recycled. Polystyrene cups produce a smaller mass of landfill waste and could produce more energy if incinerated.

4 This is up to the student, who may choose polystyrene cups for the reasons described above or may choose

paper perhaps using alternative energy sources for manufacture and transport in order to reduce the use of petroleum.

MR4.1 Bubble gum or bubble glass?

1 a The warm gum is elastic. b If it is pulled too hard it deforms permanently.2 a The cold gum snaps when it is bent, because it is

below its Tg.

MR4.2 Using spaghetti to model polymer structure

Drain the spaghetti well before putting it in the dish. Allow it to cool before attempting to turn the dish upside down. The best arrangement is usually seen on the base of the solid cake.

MR5 Check your knowledge and understanding

This activity ensures that students are aware of the learning outcomes (specification statements) that their assessment will be based on, and provides an opportunity for them to reflect on how well they understand the ideas that they have covered in this module. Crucially, it enables teachers to identify areas where individual students are less confident, and to provide appropriate additional support to improve their understanding. This activity could be used as part of the preparation for an end of module test.

Paper cup Polystyrene cup

Mass of wood and bark needed to make one cup 33 g

Mass of petroleum needed to make one cup 4.1 g 3.2 g

Mass of other chemicals needed to make one cup 1.8 g 0.05 g

Mass of one cup 10.1 g 1.5 g

Cost of one cup 5p 2p

Show, by using a tick (3), which cup needs more: steam electricity coolingwater.

333

Show, by using a tick (3), which cup produces more:wastewaterwaterpollutionmetalssalts wastegases.

3333

Can the cup be re-used? Yes Yes

Can the material from the cup be recycled? No Yes

Can the cup be incinerated? Yes Yes

How much energy is produced if 1 kg of cups are incinerated? 20 MJ 40 MJ

What ratio of material would go into landfill from the same number of cups? 6 tonnes 1 tonne

Is the cup biodegradable? Yes No

252_12_SAC A2_TT MR.indd 238 17/3/09 08:32:20



MR Answers to end of module tests

Answers to The Materials Revolution end of module test

Q Answer Maximum mark

1 (a) (i) (di)amine 1

1 (a) (ii) 1,6-diaminohexane (1) (ignore commas, dashes and spaces) 1

1 (a) (iii) +H3N(CH2)6NH3+ (1); Cl (1); the lone pair on the nitrogen accepts (or forms a covalent bond with) a proton (1)

3

1 (b) (i)

NH

O

O

HN

amide bond shown (1); completely correct (1)

2

1 (b) (ii) Two molecules combine to form a larger molecule with the elimination of a small molecule (or water) (1);

many molecules joining to form a longer molecule (1)

2

1 (b) (iii) One from: no small molecule (or water) produced (in addition polymerisation); monomers unsaturated (in addition polymerisation); polymer is just monomers added together or same empirical formula (addition)

1

1 (c) (i) Acyl chloride 1

1 (c) (ii) Hydrogen chloride/HCl 1

1 (c) (iii) Acylation 1

1 (c) (iv) Two from: it is expensive because it contains chlorine (1); it is dangerous (1); HCl formed is dangerous/toxic (1)

2

1 (d) (i) Because the number (NOT strength) of intermolecular bonds increases with chain length (allow alternatives)

1

1 (d) (ii) Instantaneous dipoleinduced dipole 1

1 (d) (iii) Hydrogen bonds (1)

N

H

O

C

correct hydrogen bond shown (1); partial charges on H, N and O (1); lone pair on O pointing along bond (1); NHO straight (1) (more of each chain can be shown)

5

1 (d) (iv) The temperature above which the polymer ceases to be brittle (or becomes flexible) or the reverse argument (1); hydrogen bonds are stronger than instantaneous dipoleinduced dipole bonds (1); more energy is needed to break the hydrogen bonds (1); (and allow) the chains (or nylon) to slide over one another (1)

4

252_20_SAC A2_EMT Answers.indd 304 17/3/09 08:34:19


Answers to end of module tests MR


2 (a) HOCH2CH2OH (1); (allow a more displayed formula)

NaOOC COONa (1) (Na+ ions not essential for second mark)

2

2 (b) (i) Permanent dipolepermanent dipole (1); 1

2 (b) (ii)

O

C

O

C

(dotted) line between C of C=O and O on another chain (1); partial charges shown (1) (more of the chain can be shown)

2

2 (c) (i) The material is stretched 1

2 (c) (ii) A crystalline area is one where the polymer chains (or molecules) are ordered (or parallel) (1); cold drawing increases the amount of crystallinity (1)

2

2 (c) (iii) Greater tensile strength or less flexible or higher Tg or Tm (1);

intermolecular bonds are stronger (not more or greater) (1);

as the chains are closer together (1)

3

2 (d) Copolymerise (1); use plasticiser (1) 2

2 (e) (i) Two from: burning (1); burying (1); recycling (1); depolymerising (1); cracking (1) 2

2 (e) (ii) Two from: conserves resources (1); reduces energy consumption (1); does not use up disposal facilities (1); reduces gas emissions (1)

2


3 (a) (i)H2N NH2HOOC COOH

2

3 (a) (ii) (Secondary) amide 1

3 (b) (i) Concentrated hydrochloric acid (1); reflux (1) (if first mark scored) 2

3 (b) (ii) Five from: use hot water (1); dissolve solid in minimum volume of water (1); filter hot (1); allow to crystallise (1); filter (1); wash (1); dry (1)

5

3 (b) (iii) Must dissolve substance well at high temperatures (1); (nearly) insoluble at low temperatures (1) (or words to that effect)

2

3 (b) (iv) Take a melting point (1); check against known melting point or pure if melts sharply (1) 2

3 (c) Tensile strength molecules closely packed or held by hydrogen bonds (1);

fire-resistant few hydrogen atoms or stable rings (1);

low density light atoms, (C, N, O) (1)

3

252_20_SAC A2_EMT Answers.indd 305 17/3/09 08:34:19

252_02-MR_SAC A2 SP.pdf252_12_SAC A2_TT MR252_20_SAC A2_EMT Answers

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A2 Support Pack Module 2 the Materials Revolution

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