Industry Tech C

8/2/2019 Industry Tech C

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Chem stry n ndustry and t eChnology

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14

Chem stry n ndustryand teChnology

As one o the most mportant roles o chem stry s tomake orms o matter that have never ex sted be ore,

t plays a central role n any mater al revolut on. TheIndustr al Revolut on o the 18th century was theresult o the large-scale extract on o ron, but themater al revolut on cont nues the development o new mater als w th structures and propert es thatserve the technolog es o today. The cons derat on o how the mater als beneit soc ety makes th s opt onpart cularly relevant to a m 8 (ra s ng awareness o themoral, eth cal, soc al, econom c and env ronmental

mpl cat ons o us ng sc ence and technology).

IBO 2007

ntroduCt on

T e c em ca ndus ry can ake raw ma er a s anurn em n o muc more va uab e produc s suc assu ur c ac d, ammon a, e ene, sod um ydrox de, andc or ne amongs o ers. Tec no ogy s used ex ens ve y

e c em ca ndus ry o produce b o ue s or manu ac upo ymers w d feren proper es. he mpor ance o c em s ry n ndus ry and ec no ogy res s on e ooc o es, med c nes and e grea var e y o consumear c es a produces. One s gn o e economdeve opmen o a coun ry s e s a e o s c em

ndus ry. For examp e, e commerc a za on o e Habprocess ke y pro onged Wor d War I by a eas one year.A mos a cen ury a er, e emerg ng e ds o nanosc enand nano ec no ogy are ead ng o unpreceden edunders and ng and con ro over e undamen a bu d nb ocks o a p ys ca ngs. h s s ke y o c angway a mos every ng - rom vacc nes o compu ers au omob e res o objec s no ye mag ned - s des gand made.

(quoted from: Nanotechnology shaping the world atom byatom, National Science and Technology Council Report,September 1999, Washington, D.C.)

C1 Iron, steel and alum n um

C2 The o l ndustry

C3 Add t on polymers

C4 Catalysts

C5 Fuel cells and rechargeable batter es

C6 L qu d crystals

C7 Nanotechnology

C8 Condensat on polymers (HL)

C9 Mechan sms n the organ c chem cals ndustry (HL)(HL)

C10 S l con and photovolta c cells (HL)

C11 L qu d crystals (HL)

C12 The chloralkal ndustry (HL)

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CHAPTER 14 (O PTION C)

364

Blast Furnace

Hopper feeding iron ore,

Tuyere

Tap hole

Molten iron

Slag hole

Tuyre

Gas outlet

1000 K

1400 K

2200 K Hot air

Molten slag

Steel furnace with heatresistant brick lining

coke and limestone

Hot air(under pressure)

Figure 1401 Blast Furnace

o P t i o n

he ma n sources o ron nc ude ron ores and scrap ron.Iron ores are m ned as ox des, Fe2O3, ( aema e), Fe3O4,(FeOFe2O3, magne e, a m xed ox de) and e su deFeS2, ( ron pyr es). he a er s roas ed n a r o orm eox de and su ur d ox de.

4 FeS2 (s) + 11 O2 (g) 2 Fe2O3 (s) + 8 SO2 (g)

C1.2 Descr be and expla n the react ons that

occur n the blast urnace. IBO 2007

A m x ure o e raw ma er a s mes one (ca c umcarbona e, CaCO3), coke (C) and ron ore ( or examp e

ron(III) ox de, Fe2O3) s ed n o e b as urnace rome op (ca ed e opper), see F gure 1401. he m x ure

s ca ed so d c arge. A arge vo ume o a r s n roducedunder pressure near e bo om o e urnace w ere coke

s ox d zed exo erm ca y o carbon d ox de as o ows:

C (s) + O2 (g) CO2 (g) + ea

he urnace s a abou 2200 K empera ure n s owerreg on. H g er up e urnace, carbon d ox de reac s

w coke o orm carbon monox de. h s reac on sendo erm c, w e urnace n s reg on coo ng 1400 K:

CO2 (g) + C (s) + ea 2 CO(g)

I na ura gas me ane, CH4 s njec ed w e oa r, ncomp e e combus on can occur o orm carbonmonox de and ess coke s requ red:

2 CH4 (g) + O2 (g) 2 CO (g) + 4 H2 (g)

I s carbon monox de a p ays e arges par n ereduc on o e ore owards e op o e urnace. Ironox des are reduced exo erm ca y:

Fe2O3 (s) + 3 CO (g) 2 Fe ( )+ 3 CO2 (g) + ea

Fe3O4 (s) + 4 CO (g) 3 Fe ( )+ 4 CO2 (g) + ea

I me ane s njec ed, e ydrogen gas produced onpar a ox da on can a so ac as a reduc ng agen :

Fe3O4 (s) + 4 H2 (g) 3 Fe ( )+ 4 H2O (g)

Coke can a so reduce e ox de, or examp e:

Fe2O3 (s) + 3 C (s) 2 Fe ( )+ 3 CO (g)

he ron produced s nks o e bo om o e urnacew ere e empera ure s g enoug o keep mo en.A e same me, because o e g empera ure, e

mes one n e c arge decomposes o orm ca c um ox deand carbon d ox de:

C1 ron, steel andalum n um

C.1.1 State the ma n sources o ron.

IBO 2007

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Pure oxygenat high pressure

Collection of waste gases

Tap hole to pourout liquid steel

Molten pig iron,scrap steel

and lime (CaO)

Holds allowconverterto be tilted

Figure 1402 A basic oxygen converter

ea + CaCO3 (s) CaO (s) + CO2 (g)

he g y bas c ca c um ox de comb nes w e ac d cs con(IV) ox de presen as sand n e mpure ore and

e amp o er c a um n um ox de (w c can be ave as anac d or a base). hese mpur es n e ore orm a mo ens ag o ca c um s ca e(IV) and ca c um a um na e(III),w c r ck es down e s ack:

CaO (s) + S O2 (s) CaS O3 ( )

CaO (s) + A 2O3 (s) CaA 2O4 ( )

he mo en ron, ca ed p g ron, s mpure and no sos rong. I con a ns abou 4 5% carbon, 1 2% s conand sma er amoun s o e emen s suc as manganese,p osp orus and su ur. he more dense p g ron es a

e bo om o e urnace and e g er s ag orms anmm sc b e ayer above ; e mo en ron and s ag areapped of every ew ours. S ag s used or road mak ng

and n e manu ac ure o cemen . A urnace can opera econ nuous y or severa years be ore needs re n ng. SeeF gure 1401.

C.1.3 Descr be and expla n the convers on o ron nto steel us ng the bas c oxygen

converter.

IBO 2001

THE BASIC OXYGENPROCESS he mos common me od o mak ng s ee s o b as pureoxygen roug e mpure mo en ron. Scrap s ee p aced n e conver er (see F gure 1402), w c s e

ed and mo en p g ron s rans erred rom e burnace. he oxygen and powdered ca c um ox de ( me)

are b own on o e sur ace o e me a a g pressuroug wa er coo ed p pes. he oxygen pene ra es n oe mo en ron and ox d zes e mpur es rap d y. A

ox des o carbon, su ur, p osp orous and s con areormed, w c escape rom e me as gases or comb ne

w me o orm s ag:

C + O2 CO2

S + O2 SO2

4P + 5 O2 P4O10

S + O2 S O2

S O2 + CaO CaS O3 (s ag)

S ag orms a ayer above e crude s ee (con a n ng an 1.5% carbon) and rema ns be nd as qu d s ee

w c s poured of. he ox da on o e mpur es s aexo erm c process and e ea evo ved as e mpurare ox d zed keeps e con en s o e urnace n a mos a e, desp e a r se n e me ng po n as mpur

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o P t i o n

are removed (reca : mpur es ower and broaden eme ng po n o a subs ance). A oy ng e emen s suc asmanganese and coba are en added o e mo en me a

o orm a oys w spec c proper es.

C.1.4 Descr be alloys as a homogeneousm xture o metals or a m xture o a metaland non-metal.

IBO 2007

An alloy s a m x ure o wo or more e emen s a eas oneo w c s a me a ; us s a omogeneous m x ure o me a s or a m x ure o a me a and non-me a n w c

e me a , ca ed e base me a , s n e muc argeramoun resu ng n me a c proper es. he a oy s madeby m x ng e a oy ng e emen (s) w e base me aw en mo en and a ow ng e m x ure o coo o orm ea oy.

C.1.5 Expla n how alloy ng can mod y thepropert es o metals.

IBO 2007

Me a s con a n a a ce o ca ons n a sea o e ec rons wan order y arrangemen o e a oms and w no r g d ord rec ona bonds presen n e me a c crys a s ruc ure(un ke, or examp e, n cova en macromo ecu ars ruc ures). As a resu , me a ayers are ab e o s de overeac o er w en a s ress s app ed o and are sot,

duc e and ma eab e proper es yp ca o me a s. hepresence o ano er e emen , w d feren y s zed a oms/ca ons, mod es e m cro-s ruc ure o e base me a by d srup ng e regu ar, repea ng a ce, see F gure 1453.h s now makes d icu or one ayer o s de overano er. W a oms suc as carbon, w c are very mucsma er an e me a ca ons, ey can n o e o eso e me a a ce d srup ng e bond ng be ween me aa oms and aga n mpac ng on e s ruc ure.

A oy ng can mod y p ys ca proper es suc as ardnessand ma eab y, as we as eng neer ng proper es suc a

ens e s reng and c em ca proper es suc as res s anceo corros on. For examp e, s a n ess s ee and bronze are

s ronger and more corros on res s an an e r baseme a s ron and copper respec ve y. Add on o d ferenamoun s o me a s o s ee c anges s ardness, res s ance

o ox da on and s reng . S m ar y w en a ow percen ago carbon s added o ron, ere s ess d srup on n e

a ce s ruc ure o e base me a . he s ee can s ben and s aped and us used o make au omob es. As

e percen age o carbon s ncreased, e d srup on ne crys a a ce ncreases, e ayers exper ence grea e

d icu y n s d ng over eac o er and a s ronger s ee sormed a can be used o bu d br dges. Fur er ncreasen carbon ( o abou 1%) makes s ee very ard and can

be used n dr b s. I e amoun o carbon becomesg er s , o abou 4% as n p g ron, s so d icu e ayers o s de over eac o er a becomes br

and o e use or cons ruc on.

C.1.6 Descr be the efects o heat treatment o steel.

IBO 2007

S ee ob a ned rom e bas c oxygen conver er (see F gure1452) may no ave e des red proper es and otenrequ res ur er ea (or mec an ca ) rea men s. hese

ead o c anges a e m cro-crys a s ruc ure eve aresu n e des red efec . herma rea men s nc ude

annea ng, quenc ng and emper ng:

Annealing s e process o s ow y ea ng s ee ando d ng a a par cu ar empera ure (some mes aboua s me ng po n ) o mod y crys a s ruc ure, a

en coo ng . he ra e o ea ng and coo ng and eempera ure s ra sed o depend on e ype o s ee

and e des red proper es. Annea ng s used o sotens ee ( a s make more duc e and ma eab e), remov

Figure 1403 How alloying can modify the properties of metals

Stress

Stress applied tometallic structure Layers are able to slide overeach other when a stress is applied Larger element disruptsregular metal lattice structure

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+ p P p s

T an um s ee W s ands g empera ures Gas urb nes, spacecrat

C rom um s ee Hard Ba bear ngs

Coba s ee H g magne c permeab y Magne s

Manganese s ee (10 - 18% Mn) Toug oo s ee ; res s an o wear Ear mov ng mac nery, ra way nes

S a n ess s ee con a n ng abou20% c rom um and 10% n cke Non-rus ng

Cu ery, s nks, car accessor es, surg cans rumen s

Figure 1404 Properties and uses of some iron alloys

s ress caused by uneven ea ng or mec an ca rea men ,c ange s e ec r ca or o er p ys ca proper es as we asremove rapped gases (w c no removed, weaken es ee mak ng suscep b e o crack ng).

Quenc ing re ers o rap d coo ng and nvo ves esudden mmers on o o me a n co d wa er or o .Quenc ng a ows e crys a s ruc ure w c s s ab ea g empera ures o ex s a ow empera ures. hesecrys a s ruc ures end o be arder an ose s ab e aroom empera ure s nce e a oy ng e emen s are rappedw n e crys a a ce mak ng e s d ng o ayers very d icu . For examp e, carbon s ee (con a n ng near y 1%carbon) s used or e produc on o cu ng oo s.

I e quenc ed s ee s oo br e, as o be made moreduc e roug a ea rea men ca edtempering w c

eads o a oss o some ardness bu w c makes e s eeess br e. Temper ng s e process o re- ea ng ardened

s ee o cer a n empera ures ( n e 200 C o 600 Crange) depend ng on e ype o s ee and en coo ng (and s done subsequen o quenc ng). Temper ng a owssome o e carbon a oms o d fuse o orm a d ferens ruc ure, mak ng e s ee soter and more duc e.

C.1.7 Descr be the propert es and uses o ronand steel.

IBO 2007

Iron s a s ny, sot, duc e, ma eab e me a o gs reng w c can be s aped n o objec s. Iron rus s o

orm ydra ed ron(III) ox de w c crumb es eas y:

4 Fe(s) + 3 O2 (g) + x H2O ( ) 2 Fe2O3 . x H2O (s)

Un ke a um n um ox de, rus s porous, a ow ng oxygenand wa er o pene ra e and con nue e corros onprocess.

Uses o ron nc ude n cans (m d s ee coa ed w a o n), ornamen a ga es, br dges, re n orc ng concrew s ee and use as a ca a ys n e Haber process. Mo

ron produced s used o make s ee . Many d feren s ee sare made, w d feren proper es or d feren uses. heamoun o carbon and e a oy ng me a s m xed w

ron arge y de erm ne e na ure o e s ee suc asens e s reng and o er use u mec an ca proper

Sma amoun s o e emen s suc as manganese, are addedo g ve des rab e qua es suc as oug ness so a

can be used as oo s ee . he presence o c rom um asan add ve o s ee n b s rus ng and produces s as ee . I a so con a ns some n cke ; orma on o a coao c rom um(III) ox de, Cr2O3 preven s e ron romrus ng. O er mpor an s ee a oys, e r proper esome uses are g ven n F gure 1404.

C.1.8 Descr be and expla n the product on o alum n um by electrolys s o alum na n

molten cryol te. IBO 2007

Aluminium s ob a ned ndus r a y by e e ec ro ysmo en a um n um ox de, A2O3. h s s ob a ned rombaux e, mpure ydra ed a um n um ox de, A2O3xH2O.he ma n mpur es n baux e are ron(III) ox de, Fe2O3 and s con(IV) ox de, S O2. he amp o er c na ure o A 2O3 s an essen a ea ure on w c s pur ca

s based. W en e mpure baux e s rea ed w concen ra ed sod um ydrox de, s con(IV) ox de anda um num ox de d sso ve:

S O2 (aq) + 2 NaOH (aq) H2O ( )+ Na2S O3 (aq)sod um s ca e

A2O3 (s)+ 2 NaOH (aq) H2O ( )+ 2 NaA O2 (aq)sod um a um na e

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Impure bauxiteFe2 O3 & SiO2 as

impurities

ConcentratedNaOH

Amphoteric Al 2O3 andacidic SiO 2 dissolve.

Basic Fe 2O3 is insoluble

Diluted and seededwith solid NaOH

Remove Fe 2 O3by ltration

Sodium silicate staysin solution

Al(OH)3 (s)precipitates out

HeatPure

Alumina

Figure 1405 Treatment of impure bauxite to obtain pure Al 2O3

Production of Aluminium

Insulation

Graphite lining(cathode)

Hole to syphon

Graphite anodes(replaced often

because of oxidation)

Molten Al

Molten electrolyte(aluminium oxide

dissolved incryolite)

Solid crust of Al2O3 protects

molten Al fromoxidation

+

o molten Al

+

Figure 1406 Production of Aluminium

o P t i o n

Iron(III) ox de and o er bas c ma er a s rema n nso ub eand are removed by ra on. he so u on s d u edand seeded w so d sod um ydrox de o reverse ereac on and prec p a e a um n um ydrox de (sod ums ca e s ays n so u on):

2H2O( )+ NaA O2(aq) A (OH)3(s) + NaOH (aq)

F na y, e a um n um ydrox de s ea ed o ob a n purea um n um ox de:

2 A (OH)3 (s) A 2O3 (s) + 3 H2O (g)

F gure 1405 summar zes e rea men o mpure baux eo ob a n pure a um n um ox de.

A um n um s so reac ve a s ob a ned by e ec ro ys so mo en sa s, requ r ng g empera ures o ma n a n

e mo en s a e. he me ng po n o A2O3 s > 2000 C

( e ca on A3+ and e an on O2 bo ave g c argedens es due o e r re a ve y sma s zes and arc arges, ead ng o very s rong e ec ros a c n erac ons

g a ce energy and a very g me ng po n ; add on ere s a g degree o cova en c arac er o bond ng so e mo en subs ance s a so a poor conduc or).A um na s m xed w mo en cryo e, Na3A F6, as aso ven w c owers e me ng po n o abou 900 C an

mproves e conduc v y. he e ec ro y e s ma n a ned as empera ure by e curren roug and us e

process s energy n ens ve. he m x ure o cryo e anda um na s e ec ro yzed n a ce w grap e (carbonpos ve e ec rodes (anodes) and a grap e ce n ng aserves as e nega ve e ec rode (ca ode), see F gure 1406.As e e ec ro ys s akes p ace, mo en a um n um (mepo n 660 C) s nks o e bo om o e ce and s run of

n o mo ds.

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369

a w : P p u

Copper Increased s reng Au omob es

Iron and s con Increased s reng ; ea res s an Fo

Up o 12% s con Lowers e me ng range We d ng

Magnes um Hardened a oy; corros on res s an Mar ne work

Z nc (w sma er amoun s o Mg, Cu and Cr) H g s reng A rp ane rames

Figure 1407 Properies and uses of some aluminium alloys

() e ec rode a reac on (ca od c reduc on; mo ena um n um produced):

A 3+ ( )+ 3 e A ( )

(+) e ec rode a reac on (anod c ox da on; oxygen gasevo ved):

2 O2 ( ) O2 (g) + 4 e

he overa reac on s:

4 A 3+ ( )+ 6 O2 ( ) 4 A ( )+ 3 O2 (g)

he O 2 produced reac s w e grap e pos vee ec rodes (anodes) o orm ox des o carbon:

C (s) + O2 (g) CO2 (g)

hus e anodes gradua y burn away and are rep acedregu ar y. Every on o a um n um requ res a a on o carbon.

C.1.9 Descr be the ma n propert es and uses o alum n um and ts alloys.

IBO 2007

he pos on o a um n um n e e ec roc em ca ser esand s e ec rode po en a sugges s ou d reac woxygen o orm s ox de and reac w d u e ac ds o

produce ydrogen:

A 3+ (aq) + 3e A (s); E= 1.66 V

H+ (aq) + e H2 (g); E= 0.00 V

he g c em ca reac v y o e e emen s ofse by rap d orma on o a very n, ard, non-porous m o

a um n um ox de, A2O3, over e sur ace, w c pro ec se me a rom ur er ox da on by oxygen or mo s u

( ron, on e o er and, orms a porous ox de rus ayera ow ng ur er rus ng o con nue undernea rus ed sur ace).

A um num s a g -we g , corros on res s an mw good e ec r ca and erma conduc v y; s versa e, ma eab e me a a can be made n o a varo s apes. Many o s a oys are very s rong. Hencea um num s an exce en c o ce w en a s rong, bu

g we g , me a s requ red. I s used bo as a s rucand decora ve me a and as an e ec r ca conduc or

g vo age ransm ss on nes.

Mos o e uses o a um num suc as saucepans, a rcratand ve c e bodywork are poss b e because o e pro ec vox de coa ng. he ckness o e ox de ayer can be

ncreased by an e ec ro y c proces known asanodizing .

h s s done by mak ng a um n um e anode dur ng ee ec ro ys s o su ur c ac d. Wa er s ox d zed o oxye anode:

2 H2O ( ) O2 (g) + 4 H+ (aq) + 4 e

Oxygen comb nes w e a um n um and ckens ox de ayer, us pro ec ng even ur er. he e ec ro yanod z ng process can be carr ed ou n e presence o dyes w c are absorbed by e ox de ayer, us co or ng

e anod zed ma er a o make su ab e or d feren suc as w ndow rames, ke es and dr nk cans. L gwe g a um num a oys or d feren needs are made by

e add on o e emen s suc as copper, magnes ummanganese, s con and z nc amongs o ers as s own nF gure 1407.

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C.1.10 D scuss the env ronmental mpact o ronand alum n um product on.

IBO 2007

A o e processes n s ee mak ng, rom e b as urnaceo e na ea rea men and e produc on o a um n um

by e ec ro ys s use remendous quan es o energy. In eproduc on o a on o s ee , approx ma e y one on o coa

s consumed and a on o s ag produced! Abou en mesmore energy s needed o produce a on o a um n um

an o produce a on o s ee . he env ronmen a efec so m n ng e ore depend on e ex rac on me od usedas we as e geograp c area n w c e ore s ound.he m ned areas can eave scars on e andscape un ess

e m n ng company dec des o revege a e e area. hewas e produc s o m n ng, tailings , and e me a was es

rom ese can be very damag ng o e env ronmen .he pur ca on o baux e produces cons derab e was e

o ron(III) ox de, e d sposa o w c , as s a v v dco our, can resu n v sua po u on.

Recyc ed a um n um rom a um n um cans requ resapprox ma e y 5% o e energy needed o produce eme a rom e ore. hus, recyc ng s essen a because saves money, energy and ue s; saves e env ronmenand e reserves o ma er a s and reduces e prob emo was e d sposa . However, recyc ng s no a wayseconom ca y eas b e as can be abor n ens ve o co ec ,sor and process. he g er e va ue o e ma er a , emore econom ca s o recyc e. hus, v r ua y a go d srecyc ed, bu on y abou a o e a um n um produced

s recyc ed and a s esser percen age o scrap ron ands ee s recyc ed.

C.2.1 Compare the use o o l as an energysource and as a chem cal eedstock.

IBO 2007

By supp y ng a arge par o e wor ds energy needs,crude o as become e mos mpor an modern rawma er a . A oug on y abou 10% o e re ned produc so crude o are used asc emical feedstock , e rawma er a s requ red or an ndus r a process o producepe roc em ca s, s s e mos s gn can sourceorgan c c em ca s. By se , crude o s no a very use uresource. However, cons s s o a m x ure o very use u

ydrocarbons w c are sources o energy suc as pe ro

and o er ue s or ranspor and o ea ng sys ems.

Pe roc em ca s are organ c compounds ound n, order ved rom, pe ro eum and are used n e manu ac ureo produc s o er an ue s. Examp es nc ude po ymers,drugs, cosme cs, pa n s, er zers, pes c des, de ergenand dyes. Frac ona d s a on o crude o produce

ubr ca ng o s, wax cand es, o n men s, po s es andc em ca s w c , n urn, are used o produce bers,agr cu ura c em ca s, syn e c rubber and so ven s.Benzene rom crude o s conver ed o am nobenzene used

n e prepara on o drugs and dyes ufs; me y benzene sn ra ed o produce TNT and a so o produce po yure ane

oams or up o s ery, nsu a on and lo a on dev ces.

C.2.2 Compare catalyt c crack ng, thermalcrack ng and steam crack ng.

IBO 2007

he pe ro eum rac ons w 1 o 12 carbon a omsn e mo ecu e are n grea er demand an o errac ons.Cracking s e break ng up o arger, ess

use u , ydrocarbon rac ons n o s or er c a n, moreuse u a kanes and a kenes w c are used as ue s andpe roc em ca eeds ock. hus, crack ng s a cr ca y

mpor an process n e o ndus ry. Crack ng can beac eved under d feren cond ons o empera ure,pressure and e presence or absence o a ca a ys , s eamor ydrogen gas. herma crack ng s a so ca edpyrolysis.For examp e, e presence o a ca a ys reduces e

empera ure a w c crack ng occurs. In e absence o a ca a ys , g er empera ure (and pressure) s requ red.S eam crack ng requ res pre- ea ng and vapour s ng

C2 the o lndustry

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371

e eeds ock and m x ng w s eam a s g erempera ures o orm ow mo ar mass a kenes.

he sma er a kanes are more eas y vapor zed and are moreuse u ue s. Crack ng can a so produce more branc ed

ydrocarbons a are be er as ue s as ey ave g eroctane numbers and us cause essknocking n eau omob e eng ne. he a kenes are eeds ock or o erpe roc em ca s and orm po ymers w ex ens ve uses.

Use o d feren eeds ocks, empera ures and ca a ys sproduce d feren produc s, see F gure 1409.

C c c ckC c ck

t c ckP ; b k

s c ck

Feedstock:reactantmolecules

Gas o : 14 20 carbon c a nqu ds (250 350 C bo ng po n

range)

Kerosene: 10 16 carbonc a n qu ds (190 250 Cbo ng po n range)

Nap a: 5 10 carbon c a nqu ds (40 190 C bo ng po nbo ng po n

range)

Reactionconditions

Lower empera ures o abou500 C

Modera e y ow pressures

Ca a ys : Powdered zeo e(a um num s ca e)*; s or ca y s ca and a um na used

S or con ac me

Modera e empera ure range:500 750 C

H g pressure o abou 70 a m.

No ca a ys

Longer con ac me

H g er empera ure range: 800 900 C

Modera e y ow pressures

No ca a ys

Very s or con ac me

Mec anismof reaction

Ion c n ermed a e; ca a ys be avesas an e ec ron pa r accep or

orm ng carboca ons

Free rad ca s ormed; CCbonds break so eac a om asone unpa red e ec ron

Free rad ca s ormed; CCbonds break so eac a om as oneunpa red e ec ron

Productsexample

C16H34 C8H18 + C8H16

Branc ed a kanes and a kenes

C12H26 C8H18 + C4H8

Branc ed a kanes and a kenes

C6H14 C3H6 + C3H8

C4H10 2 C2H4 + H2

A kanes and a kenes (+ ydrogen)

Uses of products

H g grade gaso ne (branc edc a n a kanes ncrease ue oc anera ng)

L g er rac ons used as ue Low mo ar mass a kenes used npo ymer manu ac ure; ydrogenused n ydrocrack ng

Figure 1409 Comparison of different methods of cracking

CH 3(CH 2)10 CH 3 CH 3 C CH 2 C CH 3

CH 3

CH 3

CH 3

H

CH 2 C CH 3

CH 3

Dodecane 2,2,4-trimethylpentane

+

2-methylpropene

Figure 1408 The thermal cracking of dodecane

*he powdered ca a ys n ca a y c crack ng s reao g ve lu d- ke c arac er s cs or grea er con

w e reac an s. As a resu o e decompos oydrocarbons, carbon depos s on e ca a ys reduce

s ac v y. From me o me a r s passed rougreac or so e coke s burn of o regenera e e ca a yshe combus on o coke produces energy w c s used or

ur er crack ng.

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o P t i o n

Polymers are ong c a n macromo ecu es made by jo n ngoge er many sma er repea ng un s ca edmonomers .

Polyet ene , a yp ca add on po ymer, s a g an mo ecu emade o undreds o ousands o e ene monomers jo ned oge er o make a ong c a n po ymer, po ye ene,represen ed by (C2H4)n. he emp r ca ormu a orpo ye ene s CH2, jus as s or e ene.

nCH 2= CH2 (C2H4)n

h s s an examp e o add on po ymer za on n w ca e monomers a oms are presen n e po ymer, adoub e bond s conver ed o a s ng e bond and wo ex ras ng e bonds are ormed. O er a kenes can a so undergopo ymer sa on (see FIgure 1410), e genera equa on or

ese reac ons s:

nCHX = CH2 (CHXCH2)n

C.3.1 Descr be and expla n how the propert eso polymers depend on the r structural

eatures.

IBO 2007

he grea er e average c a n eng , e grea er are en ermo ecu ar orces and ence g er e s reng and

me ng po n o a po ymer. Bes des c a n eng and IMFs,

ree o er s ruc ura ea ures are genera y mpor an nde erm n ng e proper es o add on po ymers:

1. Branc ng: Depend ng on reac on cond ons,po ye ene can be made e er as a g dens y po ye ene(HDPE) or owdens y po ye ene (LDPE) po ymer.HDPE as e branc ng. hus s a near po ymer n

w c e carbon backbone o e c a n akes up a z gzagpa ern due o e e ra edra s ruc ure or carbon bonded

o our o er a oms. Suc a s ra g c a n po ymer canpack c oser oge er. hus, s s rong and qu e r g dw a compara ve y g me ng po n (abou 135 Cand s used or mak ng r g d ar c es suc as bucke s,m k bo e cra es, d sposab e syr nges, e c. However, n

e ow dens y po ymer, s de c a ns are presen of ema n c a n. he presence o branc es n LDPE m s

ow c ose po ymer c a ns can come o eac o er, usower ng n ermo ecu ar orces, ead ng o ower dens

and me ng po n (abou 100 C). LDPE s used o makep as c bags, wrappers, squeeze bo es, p as c bow s, e c.

2. Or en a on (or pos on) o e a ky groups a ong apo ymer backbone c a n: D feren proper es ar se rom

e s ereoc em s ry o e po ymer c a ns. For examp epo ypropene s made by e po ymer sa on o propene ass own n F gure 1411.

CH 2 CH CH 3 CH 2 C

H

CH 3

n

n( )

Figue 1411 The formation of polypropene

he carbon a oms n e po ymer backbone are arrangedn a n a z g-zag manner (w e ra edra ang es) as s ownn F gure 1412.

C3 add t on Polymers

X n CHX = CH2 Monomer Polymer

H E ene Po y(e ene)

CH3 Propene Po y(propene)

C6H5 P eny e enePo y(p eny e ene), a so

ca ed po ys yrene

I X and H a oms rep acedby F Te raluoroe ene

Po y( e raluoroe ene);commerc a name: Telon

Figure 1410 Examples of addition polymerization of CHX=CH 2

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CC

CC

CC

CC

C

Figure 1412 The arrangement of the carbon backbone

he ydrogen a om and e me y s de c a n (CH3)can appear on e er s de o e backbone. I e me ygroups are a on e same s de and e ydrogen a omson e oppos e s de, a s e me y groups are orderedw e same or en a on, e po ymer s sa d o beisotactic . Re er o F gure 1413. Po ymers w regu ar

so ac c arrangemen s can pack more c ose y w s rongern ermo ecu ar orces. hus ese po ymers are oug and

are used o make bres, ropes, carpe s and au omob ebumpers. I e arrangemen s random, a s w ouany order o e or en a on o e me y groups (w c

s e more ke y), e po ymer s ca edatactic . Re er

o F gure 1413. Po ymer c a ns n a ac c po ypropy enecanno pack as c ose y and are no e d very g y mak ngpo ypropy ene sot and lex b e, w a ow me ng po nand no very s rong. I s, or examp e, used n mak ngsea an s and wa er-proo ng ma er a s.

CH 2C

CH 2C

CH 2C

CH 2C

CH 2

H H H HCH 3 CH 3 CH 3 CH 3

Isotactic polypropylene

CH 2C

CH 2C

CH 2C

CH 2C

CH 2

H H HCH 3 H CH 3 CH 3CH 3

Atactic polypropylene

Figure 1413 Isotactic and atactic arrangements

C.3.2 Descr be ways o mod y ng thepropert es o add t on polymers.

IBO 2007

Plasticizers n po yv ny c or de: he s ronger d po e-d po e n ermo ecu ar orces be ween c a ns n epo ymer po yv ny c or de (PVC) ead o a r g d p as c.P as c zers are sma mo ecu es added o a po ymer. hesereduce IMFs and a ow po ymer c a ns o s de over eaco er, produc ng a soter p as c. Med ca produc s sucas b ood bags and n ravenous dr p ubes end o be madeo po yv ny c or de con a n ng a (d e y exy p a e)

p as c zer. A 10% concen ra on o e p as c zer proda sem -r g d PVC and g er concen ra ons produce emore lex b e po ymers.

Vo a e ydrocarbons n e orma on o expandepo ys yrene: h s nvo ves e po ymer sa on o s yre

n e presence o a vo a e ydrocarbon o ow bopo n suc as pen ane, C5H12. h s produces po ys yrenecon a n ng e vo a e ydrocarbon w c , as vaporcauses e po ys yrene o expand o severa mes or g na s ze and ence ave a reduced dens y. heseexpanded po ys yrenes are very good erma nsu a orsand are used, or examp e, n mak ng d sposab e cofeecups.

C.3.3 D scuss the advantages andd sadvantages o polymer use.

IBO 2007

Po ymers are g , mpermeab e o wa er and can bep gmen ed, g v ng r se o ar c es w a w de var ea rac ve co ors. S nce weak van der Waa s orces exbe ween po ymer c a ns, mos po ymers become sotand me on ea ng so ey can be mo ded o orm

ms and s ee s as we as rods and ubes. Po ymerscon a n s rong cova en bonds w n e po ymer c amak ng em res s an o c em ca reac ons and ey agenera y ave good e ec r ca nsu a on proper es. advan age o po ymers s a ey can be spec a y ma

o ex b d feren proper es suc as:

S reng and g dens y: Examp es nc ude HDPEr g d PVC, po ys yrene.

F ex b y and ow dens y: Examp es nc ude LDlex b e PVC.

Insu a ors: Po ymers suc as expanded po ys yrene, andpo y e raluoroe ene (PTFE) are exce en examp es.

D sadvan ages o p as cs: he source o mos syn epo ymers s pe ro eum, a nonrenewab e resource, sous ng p as cs ur er dep e es s. O er d sadvan

nc ude e vo ume occup ed by p as cs n and s. hcan ave a subs an a env ronmen a mpac as nondegradab e ma er a s co ec and ox c umes, caused by burn ng p as cs are re eased. Some o er d sadvan ageappear under d sposa o p as cs.

D sposa o p as cs s o key mpor ance s nce currengrea dea o ends up n and s. here are our poss bapproac es o reduc ng s:

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o P t i o n

nC nerat onBur ed p as cs represen a g energy con en n and s.Produc s o comp e e combus on o p as cs are pr mar y carbon d ox de and wa er and can ead o a arge reduc on

n p as c was e w e produc ng use u energy. However,nc nera on does presen prob ems name y: ( ) carbon

d ox de produced s a green ouse gas, ( ) c or na edpo ymers suc as PVCs produce ydrogen c or de oncombus on, ead ng o ac d ra n, ( ) e nc nera on

empera ure s no g enoug , ox c c em ca s suc asd ox ns are ormed and ( v) some pr n ed p as c con a ns

eavy me a s suc as ead and cadm um, w c areox c. A so, po yure ane oams produce ox c vapours

( ydrogen cyan de and n r es) w en burn .

B odegradaB l tyhe use o bac er a and ung o break down p as cs:

M croorgan sms are ab e o break down na ura po ymerssuc as ce u ose and s arc n o s mp er mo ecu es us ngenzymes. hus, s arc can be ncorpora ed n o a p as c omake b odegradab e. he ques on o b odegradab y scomp ca ed by e ac a and s are oten ned o s op

eac ng n o e wa er ab e. Un or una e y, suc cover ngproduces anaerob c (oxygen ree) env ronmen s w ereb odegrada on by aerob c m cro-organ sms occurs very s ow y or canno ake p ace.

r eCyCl ngRecyc ng can reduce e amoun o new p as cs

manu ac ured. he amoun o p as c recyc ed ranges rom very e o as muc as 50% depend ng on governmenpo c es. here s a c ear ncrease n e recyc ng o p as cbo es made o PET (po y e y eneterep a e) w c seasy o me and reuse. h s s rue o any po ymer a

s no ex ens ve y cross nked. he mo en po ymer cane er be used n e manu ac ure o new produc s ewas e s made o s m ar monomers or can be used omake p as c o ower qua y w appropr a e uses suc asc eap p as c umber. However, e sor ng o p as c was ecan be qu e abour n ens ve.

Conservat onAs a soc e y we ave become vo um nous users o p as cs w c are made rom a nonrenewab e resource.Conserva on, recyc ng and m n ma use o p as cs s ou dbe a key s ra egy n ex end ng e e o nonrenewab eresources (Reduce, Reuse, Recyc e).

Ca a ys s are o v a mpor ance n b oc em s ry (knownas enzymes w c are pro e n based), env ronmen ac em s ry (suc as p a num and r od um based ca a y c

conver ers), and ndus r a c em s ry. Examp es nc uderon n e manu ac ure o ammon a, vanad um(V) ox de ne Con ac process or e manu ac ure o su p ur c ac d,

Ze g er-Na a organome a c ca a ys s n e produc on g dens y po ye ene, powder s ca/a um na n ca a y

crack ng, n cke n e ydrogena on o vege ab e o s manu ac ure margar ne amongs many o ers.

As d scussed n C ap er 5, a ca a ys s a subs ance ancreases e ra e o a c em ca reac on w ou be n

c em ca y c anged. I s usua y requ red n smaamoun s and s no used up n e reac on ( n b ors ornega ve ca a ys s decrease e reac on ra e). A ca a ys

speeds up a reac on by ower ng e ac va on energy o a reac on nvo v ng d feren rans on s a e(s) andprov d ng an a erna e pa or o occur ( ke a unne

roug a moun a n) See F gure 1414 (a) and (b). Wower ac va on energy, a arger number o par c es can

now reac success u y. However,H o e reac on sno afec ed ( rema ns e same); ne er s e pos ono equ br um; a ca a ys ncreases e ra e o bo

orward and reverse reac ons equa y.

Exothermic reaction

E a uncat E a uncat >E a catcat E a cat

PE ReactantsH = -

Progress of reaction (or time)

Figure 1414 (a) Exothermic reactions

C4 CatalystsC.4.1: Compare the modes o act on o

homogeneous and heterogeneouscatalysts.

C.4.2: Outl ne the advantages andd sadvantages o homogeneous andheterogeneous catalysts.

C.4.3: D scuss the actors n choos ng a catalystor a process.

IBO 2007

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Endothermic Reaction

E a uncat E a uncat > E a catcat

PE E a cat Products= +

Progress of reaction (or time)

Reactants

H

Figure 1414 (b) Endothermic reactions

he efec o a ca a ys can a so be s own on a Maxwe -Bo zmann d s r bu on curve: In e presence o a ca a ys ,

ac va on energy,Ea s owered v a an a erna e pa way.Many more par c es now ave e m n mum energy oreac and ra e ncreases. Re er o F gure 1415.

E a cat

E a uncat E

F r a c t

i o n o

f m o

l e c u

l e s

Figure 1415 A Maxwell-Boltzmann distribution curve

Catalysts can reac a e sur ace or par c pa e ne reac on. In sur ace ca a ys s suc as n cke n e

ydrogena on o a kenes, e sur ace o e ca a ysprov des ac ve s es on w c e reac on can occur wreduced ac va on energy. d b ock me a s suc as ron andn cke be ave as sur ace ca a ys s. In ermed a e ca a ys ssuc as a um n um c or de, A C3, used n e a ogena onand a ky a on o benzene reac w a reac an o orm an

n ermed a e (A C4) and are regenera ed a e end o ereac on.

Ca a ys s can be c ass ed as omogeneous ore erogeneous ca a ys s:

In omogeneous catalysis , e reac an s and e ca a ysare n e same p ase; e ca a ys a ows e reac on o

ake p ace by a d feren mec an sm, w owerEa, usncreas ng reac on ra e. In s process e ca a ys reac s

n a s ep o e mec an sm and s regenera ed a a as ep. An examp e n aqueous so u on s e reac obe ween S2O8

2 (aq) and I (aq) n e presence o Fe2+ (aq)as a ca a ys :

S2O82 (aq) + 2 I (aq) 2 SO4

2 (aq) + I2 (aq)

Fe2+ (aq) be aves as an n ermed a e ca a ys : s ox do Fe3+ (aq) and reduced o Fe2+ (aq) n e subsequen

s ep:

S2O82 (aq) + 2 Fe2+ (aq)

2 SO42 (aq) + 2 Fe3+ (aq)

2 I (aq) + 2 Fe3+ (aq) 2 Fe2+ (aq) + I2 (aq)

Ano er examp e s e orma on o es ers (swee smecompounds) used n e per ume and ood ndus ry (sucas e sme o bananas, peac es, per umes) a use

concen ra ed su ur c ac d, H2SO4, as a ca a ys :

CH3COOH (aq) + C2H5OH (aq) CH3COOC 2H5 (aq) + H2O ( )

E ano c ac d + e anoe y e anoa e + wa er

he orward reac on s e ac d-ca a ysed orma on oe es er, and e reverse reac on s e ac d-ca a ys

ydro ys s o e es er; bo are examp es o omogeneouca a ys s.

In eterogeneous catalysis , e reac an s and e ca a ysare n d feren p ases, yp ca y a so d ca a ys wreac an s be ng n e gas or qu d p ase w ere e ca aprov des e reac ve sur ace upon w c e reac on ca

ake p ace. Examp es nc ude:

1. he Contact Process : Produc on o SO3 or emanu ac ure o su ur c ac d, e k ng o c em ca s:

2 SO2 (g) + O2 (g) 2 SO3 (g)

2. he Haber Process : Produc on o ammon a ormanu ac ure o er zers, exp os ves (TNT), e c.

N2 (g) + 3 H2 (g) 2 NH3 (g)

3. Hydrogena on o an a kene con a n ng C= C bonds(an examp e o an add on reac on):

C2H4 (g) + H2 (g) C2H6 (g)

H+ (aq)

H+ (aq)

V2O5 (s)

Fe (s)

N (s)

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o P t i o n

h s ype o reac on s used n e ood ndus ry o producepar a y sa ura ed compounds, or examp e, margar ne.

Enzymes ave some c arac er s cs o bo omogeneousand e erogeneous ca a ys s. L ke omogeneous ca a ys smos enzymes occur n e same p ase as e reac an s,bu ke e erogeneous ca a ys s e reac an s b nd o anac ve s e on e sur ace o e enzyme mo ecu e. Enzymesare un que n a ese are very spec c, eic en andwork bes a body empera ure. Enzymes can ca a yse on y one par cu ar reac on un ke norgan c ca a ys s suc asa um na, w c ca a yses many reac ons. Enzymes d fer

rom norgan c ca a ys s n e r ncred b y g er ca a y cac v y. In mamma s and b rds resp ra on occurs a 37 Cand requ res numerous s eps, eac one ca a ysed. In e

ab, e reac on occurs above 600 C.

modes o a Ct on o

h omogeneous a nd h eterogeneous Catalystsab b

c pTrans on me a ons ex b re a ve y s ab e mu p eox da on s a es by ga n ng or os ng e ec rons n redoxreac ons. An examp e o omogeneous ca a ys s s ero e o Iron(II)/(III) n speed ng up e s ow reac onbe ween ac d ed ydrogen perox de and od de ons. he

ron(II) s ox d sed by e perox de o ron(III) w c s

en reduced by e od de ons o regenera e ron(II):

H2O2 (aq) + 2 H+ (aq) + 2 Fe2+ (aq) 2 H2O( )+ 2 Fe

3+ (aq)

2 I (aq) + 2 Fe3+ (aq) I2 (s) + 2 Fe2+ (aq)

hese reac ons occur more rap d y because bo aveower ac va on energ es an e reac on w ou e

use o e ca a ys .

An examp e o a e erogeneous ca a ys nvo v ng c angen ox da on number o e rans on me a on ca a ys s

e use o vanad um(V) ox de n e Con ac process. Ine rs s ep, su ur d ox de s ox d sed o su ur r ox de

and e vanad um(V) s reduced o V(IV); subsequen y,V(IV) s ox d sed by oxygen o regenera e e ca a ys :

SO2 (g) + V2O5 (s) SO3 (g) + V2O4 (s) (or 2 VO2)

V2O4 (s) + O2 (g) V2O5 (s)

t p cEnzymes are very comp ex n s ruc ure. he reed mens ona s ape o e g obu ar pro e n mo ecu es scruc a o e ca a y c ac v y o enzymes. Enzymes ansubs ra es are on y efec ve ey ave spec c reed mens ona s apes w c comp emen one ano er ( e

ock and key mode ). I e enzyme c anges s s apeor arrangemen , e subs ra e w no onger be ab e ob nd o e ac ve s e and e enzyme s rendered non-

unc ona . h sdenaturation can ake p ace w en esurround ng env ronmen c anges even s g y. h s may be broug abou n severa ways suc as a var a on n e

empera ure or pH o e so u on, or by e presence o eavy me a ons (see C aper 13, Sec on B 7.7).

For examp e, an ncrease n empera ure ncreases enzyma creac on ra es up o a cer a n po n as e subs ra es co dw ac ve s es more requen y as e mo ecu es mov

as er. However, e speed o e reac on drops s arp y

w en e empera ure reac es a cer a n po n . Here, eerma ag a on o e enzyme d srup s e ydrogenbonds, on c bonds and o er noncova en n erac ons

a s ab ze s ac ve s ruc ure. I e reed menss ruc ure s c anged as a resu o empera ure, eenzyme ac v y s afec ed. A enzymes ave an op mum

empera ure a w c ey are no ye dena ured and esubs ra es co de as es w e enzyme. In umans,enzymes ave an op mum empera ure o abou 37 C,abou e same as e n erna body empera ure. Beyond

s empera ure, e c ange n e enzyme s ruc ureafec s e ac ve s e (usua y rrevers b y) and e radrops s arp y. F gure 1416 s ows e var a on o reac on

ra e w empera ure w en e subs ra e concen ra onand pH and o er ac ors are e d cons an .

r a t e

20 30 40 50 T/C O p t i m u m

t e m p e r a t u r e

Figure 1416 The effect of temperature on enzymeactivity

Pro e ns con a n groups suc as NH2 and COOHand are suscep b e o pH c anges. Ex reme c anges npH va ues dena ure suc on sab e enzymes render ng

em nefec ve. A ow or g pH va ues, e enzyme srrevers b y dena ured and e ra e drops s arp y. W n a

narrow pH range, e enzyme s ruc ure c anges revers b y and eac suc enzyme works op ma y a a spec c pH.hus e max mum ra e or e enzyme c ymo ryps noccurs around pH 8 and or peps n s occurs a pH

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2. However, e enzyme nver ase w c ca a yzes eydro ys s o e neu ra sucrose mo ecu e as a cons an

ra e n e pH range 3.3 o 7.5. hus, an enzyme s ac ng

on an e ec r ca y neu ra subs ra e mo ecu e, or w ere ec arge p ays no ro e n e ca a yzed reac on, c anges npH ave e efec on e ra e o s reac on. F gure1417 s ows e var a on o reac on ra e w pH w en

e subs ra e concen ra on, empera ure and o er ac orsare e d cons an .

r a t e

4 6 8 10 14pH

Figure 1417 The effect of pH on enzyme activity

Heavy me a ons can a so d srup some enzyme ac v y.W en a eavy me a on s presen a e ac ve s e,subs u on o a d feren me a on or e or g na

on causes e enzyme o ma unc on and dena ure,par cu ar y w ere eavy me a ons can b nd or c e a e

o e SH groups n pro e ns o orm SMS ypearrangemen (see, a so C ap er 13 Op on B).

a b c he reg on o e ca a ys w c b nds o one or morereac an s s ca ed eactive site . For enzymes e ock andkey mode us ra es ow e subs ra e mo ecu e b ndsrevers b y o e ac ve s e o orm e enzyme-subs ra ecomp ex ( n w c e subs ra e orms weak bonds), ereac on s ca a ysed o orm e enzyme-produc comp exand e produc s eave o make e ac ve s es ava ab e

or ur er ca a y c ac v y. Re er a so o Op on B.

He erogeneous ca a ys s con a n ac ve s es a are o adsorb one or more reac an s on o o ac a e

reac on and reduce e ac va on energy. Adsorp on

s an ncrease n e concen ra on o one subs ancee reac an , a e sur ace o ano er, e ca a ys (d feren o absorp on). Cons der e ydrogena on o ana kene a e sur ace o n cke ca a ys : on adsorp on,e ec ron pa r a o ds e wo ydrogen nuc e oge

n ydrogen and e e ec ron pa r n a kene orm ng bond o e doub e bond are a rac ed o e ca a ysh s weakens e HH bond and e C= C doub e bondmak ng e reac on be ween e wo as er. Once produc s ormed as weaker a rac on or e acs e and eaves, ree ng e ac ve s e o adsorb oreac an mo ecu es o s sur ace.

Good e erogeneous sur ace ca a ys s suc as n ckep a num and r od um adsorb e reac an s(s) suic en y

o ower e ac va on energy or reac on o ake pbu do no adsorb e produc mo ecu e w c s re easeda ow ng e process o con nue. Me a s suc as sadsorb reac an mo ecu es oo weak y (or ungs en w cadsorbs oo s rong y) o be use u as sur ace ca a ysF gure 1418 s ows e advan ages and d sadvan ages o

omogeneous and e erogeneous ca a ys s.

aCtors n s eleCt ng a C atalysts cEnzymes are g y se ec ve and ca a yse on y one ypereac on. Good se ec v y means on y e des red produ

s produced and unwan ed by-produc s are no ormed.I a ca a ys eads o unwan ed produc s, ex b s se ec v y. Zeo es are examp es o so d ca a ysregu ar mo ecu ar s ze porous o es (a so ca ed pores andc anne s). Zeo es are more se ec ve as on y mo ecu es

e spec c s ze can en er e o es and on y produc s os ze sma er an e o es can ex .

Homogeneous catalysts Heterogeneous catalysts

Advantages H g ac v y as a e ca a ys sexposed o e reac an s

H g se ec v y or s ng eproduc as e ca a ys asun que ac ve s es

So d ca a ys s are easy o remove andrecover rom produc s by ra on

Long ca a y c e

D sadvantages D icu o recover romreac on m x ure or reuse

On y efec ve on e sur ace encemos o e so d s no used; a so, any coa ng on sur ace reduces ac v y

Figure 1418 Advantages and disadvantages of various catalysts

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o P t i o n

A good examp e o a zeo e ca a ys n ac on s ocompare e me y a on o me y benzene us ng A C3 or zeo e as a ca a ys . S nce e me y group s or o,para (2,4-) d rec ng (see Op on G.10), e produc s are1,2- and 1,4-d me y benzene. W en A C3 s used, e1,2- somer s ormed n e arger amoun as ere are woor o pos ons on benzene, bu on y one para pos on.A sma amoun o 1,3- somer s a so ormed. However,us ng zeo e o spec c s zed pores, e produc s a mosen re y e 1,4- somer s nce e o er wo somers ave a

arger cross-sec on an e d ame er o e pores.

1,2-dimethylbenzeneCH 3

CH 3

1,3-dimethylbenzeneCH

3

CH3

1,4-dimethylbenzeneCH 3

CH 3

Figure 1419 The use of zeolite catalyst

e c c f ch s e s us ow rap d y e ca a ys orms e des redproduc . For examp e, zeo es expose a muc argersur ace area o reac an s produc ng grea er eicacy anA C3. Hydrogen perox de s decomposed by a var e y o ca a ys s nc ud ng manganese(IV) ox de, s ver, p a numand od de on as we as e enzyme ca a ase. he enzyme,w c con a ns ron a s ac ve s e, s, owever, e mosefec ve.

ab w k / cOne o e d sadvan ages o enzymes s a ey workunder narrow empera ure and pH ranges and are eas y dena ured beyond ese ranges. On e o er and,

e erogeneous ca a ys s suc as ron are efec ve under vas y d feren cond ons o empera ure and pressure,

or examp e n e Haber process.

e p cCa a ys s are n grea demand w es ma es o 80% oa c em ca ndus r es us ng ca a ys s. h s ra ses concern over e r env ronmen a mpac . For examp e,

e demand or e p a num group e emen s (p a num,r od um, pa ad um) used n ca a y c conver ers s nce e1970s as ncreased grea y. Some o ese me a s are os

o e env ronmen and ra se e ssue o po en a ear sks s nce, a oug c sp a n and o er p a num baseddrugs are used n e rea men o cancer, ese ex bsevere s de efec s and ox c y o v ng ce s. D spos

o spen ca a ys s s a concern oug e cos o ep a num group o e emen s makes a conv nc ng argumenor recyc ng. A so, researc s prov d ng new ca a ys s n

p ace o ac d ca a ys s o reduce env ronmen a mpac .

C pA ca a ys can be po soned or rendered nefec ve. heeic ency o a ca a ys usua y decreases w me as becomes nac ve due o mpur es n e reac on m x urs de reac ons, or s ac ve sur ace becomes coa ed andunava ab e or ac v y suc as e coke coa ng on a um nor s ca n ca a y c crack ng. he coke can, owever, beburn of o regenera e e ca a ys . Enzymes dena ure by

e efec o empera ure, pH and eavy me a ons suc asHg2+ and Pb 2+ e r s ruc ures are a ered.

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A fuel cell s a dev ce a conver s e c em ca energy o ue s d rec y n o e ec r ca energy. Norma y ue sare burn conver ng c em ca energy o ea w c canbe conver ed o e ec r c y by genera ng s eam o urn

urb nes. h s s a g y neic en me od; ue ce s eado a muc more eic en convers on o c em ca energy

d rec y n o e ec r ca energy o genera e power.

In a ydrogen-oxygen ue ce , e nega ve e ec rode

(anode) s made o porous carbon mpregna ed w eca a ys Pd or P ; e pos ve e ec rode (ca ode) s a somade o porous carbon con a n ng e ca a ys P . hesee ec rodes are separa ed by aqueous ydrox de e ec ro y e(KOH or NaOH) and e ox da on o ydrogen gas by oxygen gas akes p ace n a con ro ed manner.

H2 O2

Porous carbon

with catalyst

ElectrolyteK + OH

H2O

electrodes

e e

Anode Cathode+

Figure 1420 Hydrogen-oxygen fuel cell

he ox da on process eads o e oss o e ec rons by eydrogen gas, H2 a e nega ve e ec rode (anode). he

e ec rons low ou o e ue ce and back o e pos vee ec rode (ca ode), v a an ex erna c rcu o reduce eoxygen gas, O2 o ydrox de ons, OH

. Mos common y,e reac ons ake p ace n bas c so u on:

() anode ox da on a reac on:2 H2 (g) + 4 OH

(aq) 4 H2O ( )+ 4 e

(+) ca ode reduc on a reac on:O2 (g) + 2 H2O ( )+ 4 e

4 OH (aq)

Overa reac on:2 H2 (g) + O2 (g) 2 H2O ( )

he ne resu s e ox da on o H2 a e () anodee ec rode and and e reduc on o O2 a e (+) ca odee ec rode.

Ha reac ons n ac d c cond ons are a so poss b e:

() anode ox da on a reac on:2 H2 (g) 4 H

+ (aq) + 4 e

(+) ca ode reduc on a reac on:O2 (g) + 4 H

+ (aq) + 4 e 2 H2O ( )

Advan ages and d sadvan ages o ue ce s: Fue ce sg y eic en (70-80%) s nce ey conver e c em c

energy o e ue s d rec y o e ec r ca energy. hus grea y reduce erma po u on, as we as be ng po u ng n genera as wa er s e produc , so ere re ease o green ouse gases rom e combus on o oss

ue s, oug no e a e ec ro ys s o wa er s ua source o ydrogen gas or e ue ce , e power

e e ec ro ys s may we ave come rom oss ue pFue ce s a so end o be g we g . On e o er

ue ce s can exper ence ec n ca prob ems rang ng reaks o corros on and ca a y c a ures. he danger

o s or ng and ranspor ng ydrogen gas a so ave obe cons dered. Fue ce s are used n e space program.hese usua y opera e a abou 70-140 C, genera e abou0.9 V and e wa er produced can be pur ed and used

or dr nk ng. Some ue ce s are used or commerc aproduc on o e ec r c y n Japan. A grea dea o resea

as aken p ace o make ue ce s or e au o ndus rorder o reduce e dependence on non-renewab e ue .A so, e produc on o carbon d ox de green ouse gas

s reduced and ess s re eased n o e env ronmen . Acomb na on o ue ce and e ec r ca y powered yso u ons are a so be ng deve oped.

C.5.2 Descr be the work ngs o rechargeablebatter es.

IBO 2007

Rec argeable batteries are examp es o secondary ce s.hese e ec roc em ca ce s are revers b e, and can berec arged; e reac an concen ra on can be res ored by app y ng an ex erna source o e ec r c y n e oppod rec on.

C5 uel Cells and reChargeaBleBatter es

C.5.1 Descr be how a hydrogenoxygen uelcell works.

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o P t i o n

Lead-ac d storage battery

hese are used n au omob es and are an mpor anexamp e o rec argeab e ba er es. hey use ead p a es ( nprac ce an a oy) and modera e y concen ra ed su ur cac d as e e ec ro y e (see F gure 1421). he ead reac sw e ac d o produce a coa o ead(II) su a e on boe ec rodes. W en e ba ery s c arged up, a e e ec rode

n o w c e ec rons low, e ead(II) su a e s reduced oead me a (ox da on s a e = 0):

PbSO4 (s) + 2 e Pb (s) + SO4

2 (aq)

and a e e ec rode a oses e ec rons e ead(II) su a es ox d sed o ead(IV) ox de:

PbSO4 (s) + 2 H2O ( ) PbO2 (s) + 4 H

+ (aq) + SO42 (aq) + 2 e

h s removes wa er and produces su ur c ac d, so econcen ra on o e ac d e ec ro y e ncreases.

W en e ba ery s used o power an ex erna oad esereac ons are reversed, so a e e ec rode a be aves as

e nega ve erm na , e ead anode s ox d sed o ead(II)su a e:

Pb (s) + SO42 (aq) PbSO4 (s) + 2 e

A e e ec rode a ac s as e pos ve erm na , eead(IV) ox de ca ode s reduced o ead(II) su a e

PbO2 (s) + 4 H+ (aq) + SO4

2 (aq) + 2 e

PbSO4 (s) + 2 H2O ( )

he overa reac on or e d sc arg ng process s:

Pb (s) + PbO2 (s) + 2 H2SO4 (aq) 2 PbSO4 (s) + 2 H2O ( )

h s consumes su ur c ac d so e concen ra on o e ac d decreases. hus, e s a e o a ba ery can be

de erm ned rom e dens y o e e ec ro y e so u onus ng a ydrome er.

he ba ery s c arged by e a erna or w e underopera on n an au omob e; a la ba ery can be c argedby a ba ery c arger and e reverse reac on akes p ace:

2 PbSO4 (s)+ 2 H2O ( ) Pb (s)+ PbO2 (s)+ 2 H2SO4 (aq)

(+) electrode, cathodemade of PbO 2 plates

() electrode, anode made of Pb plates

Sulfuric acid electrolyte

+

Figure 1421 The lead-acid storage battery

he vo age produced per ce s 2V. hus, or a 12V carba ery, s x 2V ce s are arranged n ser es. h s produces 12 vo s bu n erna res s ance a so ncreases, us produc ng

ess curren an s x s ng e ce s.

Advan ages o ead ac d ba ery: I can de ver arge amoun so energy or s or me per ods and s rec argeab e.D sadvan ages: Ow ng o e g dens y o ead, ere

s a g mass o c arge ra o ( eavy) and ac d sp age sa poss b y, a oug car ba er es now end o come

sea ed con a ners.

N ckelCadm um (N Cad) Batter es

hese ba er es are rec argeab e, g we g dry ce sa produce a cons an po en a o 1.4V:

A e nega ve cadm um e ec rode ( e anode), anox da on a reac on akes p ace n e presence o

ydrox de ons and Cd s ox d zed o Cd2+:

Cd (s) + 2 OH (aq) Cd(OH) 2 (s) + 2 e

A e pos ve n cke e ec rode ( e ca ode), a reduc oa reac on occurs w ere N3+ n N O(OH) s reducedo N2+:

e + N O(OH)(s) + H2O ( ) N (OH)2 (s) + OH (aq)

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381

he overa reac on s:

Cd (s) + 2 N O(OH) (s) + 2 H2O ( ) Cd(OH) 2 (s) + 2 N (OH)2 (s)

Ox da on numbers: 0 +3

+2 +2

Cadm um s be ng ox d zed rom 0 o +2; n cke sreduced rom +3 o +2. Inso ub e ydrox des o cadm umand n cke depos on e e ec rodes and a reac onsare eas y reversed dur ng c arg ng. he reduc ng agencadm um and ox d z ng agen N O(OH) are regenera edon rec arg ng:

Cd(OH) 2 (s) + 2 N (OH)2 (s) Cd (s) + 2 N O(OH) (s) + 2 H2O ( )

A N -Cd ba ery exper ences e memory efec w coccurs w en s c arged ater be ng ncomp e e yd sc arged ( s appens as a resu o unreac ve sur ac

ormed on e e ec rodes a s ops reac ons dur nrec arg ng). I s us bes o comp e e y d sc arge ba ery be ore be ng re-c arged. he n cke and cadm umare more expens ve, produce a ower vo age, bu ave

onger e an ead-ac d accumu a ors. Cadm um s oo many e orms and ere are env ronmen a concerns

abou e d sposa o ox c cadm um con a n ng ba e

F gure 1422 g ves e s m ar es and d ferences be we

ue ce s and rec argeab e ba er es.

c c b b

s d f c

Bo dev ces conver c em ca energy d rec y n o e ec r ca energy us ngspon aneous redox reac ons.

Bo ave s m ar modes o opera on,name y, nega ve anode e ec rodes w erean ox da on a -reac on akes p aceand pos ve ca ode e ec rodes w ere areduc on a -reac on akes p ace.

Fue ce s are energy convers on dev ces w ereas rec argeab e ba er esare energy s orage dev ces.

Fue ce s requ re a cons an supp y o reac an s (an examp e o an ope

sys em) and produce e ec r ca energy on y as ong as ue s madeava ab e o e ce . Ba er es on e o er and ave s ored c emenergy n a c osed sys em and prov de power un e s ored c em caare used up.

Ba er es can be rec arged; s uses e ec r ca energy o carry oue reverse reac on. Rec arg ng akes a ba ery ou o opera on. A

ue ce , on e o er and, does no need rec arg ng ke a ba ery.Ra er, can ave a con nuous supp y o ue (by rep ac ng emp y con a ners w u ones) prov d ng onger opera ng e.

he e ec rodes n ue ce s are made o ner ma er a s (suc as porouscarbon mpregna ed w p a num and pa ad um as a ca a ys ) w

a ow e movemen o ydrogen, oxygen and wa er.Fue ce s are curren y more expens ve an rec argeab e ba er es.

Figure 1422 Comparing fuel cells and rechargeable batteries

C.5.3 D scuss the s m lar t es and d ferencesbetween uel cells and rechargeablebatter es.

IBO 2007

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o P t i o n

l - bhe very g ac v y o um me a means an ox de

ayer orms over e me a eas y reduc ng e con acw e e ec ro y e n a ba ery. h s s overcome n e

um- on ba ery w c con a ns no me a and nvo vese movemen o um ons be ween e nega ve anode

and e pos ve ca ode e ec rodes roug e e ec ro y e,a um sa n an organ c so ven . Suc ce s use carbongrap e as e nega ve e ec rode (anode). L um

ons can en er ( nser ) n o e grap e a ce w anapprox ma e L C6 compos on. he pos ve e ec rode(ca ode) s a me a compound, or examp e o ormu aMO2, suc as manganese(IV) ox de (MnO2), coba (IV)ox de (CoO2) or n cke (IV) ox de (N O2). Ox da onoccurs a e nega ve e ec rode (anod c ox da on):

L C6 L+ + 6 C + e

L um ons n so u on en er e ox de pos ve e ec rodew ere reduc on occurs (ca od c reduc on):

L + + e + MnO 2 L MnO2

he ne resu s e movemen o um ons rome nega ve anode o e pos ve ca ode: he overa

reac on s:

L C6 + MnO 2 6 C + L MnO2

I s e d ference n e ree energy o um be ween

L C6 and L MnO2 a powers e ce . he e ec rodesare ca ed nser on e ec rodes as sma um ons canbe nser ed (and removed) n o e e ec rode a ce. Onrec arg ng, e reverse reac on akes p ace. he um-

on ba ery does no sufer rom e memory efec aN -Cd ba er es do.

l qu d Crystalshe s a es o ma er depend on e mob y o par c esand yp ca y nc ude so d, qu d and gas w c depend on

empera ure. For examp e, wa er s ce be ow 0 C, wa erbe ween 0 and 100 C and wa er vapour above 100 C (a 1a mosp ere pressure). In so ds, par c es ave an order y,

ree d mens ona arrangemen n w c mo ecu es arexed n pos on and or en a on (po n ng n e same

d rec on) and are arranged n a repea ng pa ern o g ve apar cu ar crys a a ce. In qu ds, e mo ecu es are

o move abou random y and can c ange e r or en a on( yp ca y, qu ds occupy a e more space an sowa er and ce are an excep on due o ydrogen bond ng n

ce a g ves r se o o es n e crys a s ruc ure). Ord naqu ds are ca edisotropic (mean ng ndependen o

d rec on) as e mo ecu es are random y arranged, aveno or en a on order and ex b no ong range order. hed s r bu on o e par c es s suc a , overa , ord n

qu ds ave e same p ys ca proper es suc as op camagne c and e ec r ca proper es w en v ewed rom any d rec on.

On e o er and, some subs ances ex s n w a s ca ede mesophase (meso mean ng be ween), some mes

ca ed e our s a e. For examp e, c o es ero myr s as a so d be ow 71 C and a c ear qu d above 86 C. In

be ween, ex s s as a c oudy qu d. Suc qu d crys a(LCs) ave some order bu a so some ab y o low, name y

ese are n a p ase w order be ween a o a qu dand a so d. here s a degree o or en a on o mo ecu es

n LCs ke a so d, bu mo ecu es a so move o d feren

C6 l qu d CrystalsC.6.1 Descr be the mean ng o the term l qu d

crystals.

C.6.2 D st ngu sh between thermotropic andlyotropic l qu d crystals.

C6.3 Descr be the l qu d-crystal state n termso the arrangement o the molecules andexpla n thermotrop c behav our.

C.6.4 Outl ne the pr nc ples o the l qu d-crystald splay dev ce.

C.6.5 D scuss the propert es needed or asubstance to be used n l qu d-crystald splays.

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383

pos ons, a s, a oss o order n e pos on akes p aces m ar o a qu d, us e apparen con rad c on n ename: qu d crys a (LC).

LCs are lu ds a ave p ys ca proper es (suc ase ec r ca , op ca and e as c y) a are dependen on

e mo ecu ar or en a on re a ve o some xed ax s ne ma er a , mak ng em un que n e r proper es and

uses.

E onga ed, modera e s ze organ c mo ecu es end o ormqu d crys a s a or en on e r onger ax s, a ougqu d crys a s are no res r c ed o e onga ed mo ecu es;

d sc- ke and banana-s aped mo ecu es o qu d crys a sare a so poss b e. One examp e o an e onga ed organ c

qu d LC s ca ed MBBA n w c e benzene r ngs orma p anar ske e on as s own n F gure 1423.

CH N C 4H9OCH3

Figure 1423 Structural formula of MBBA

Examp es o LCs nc ude b o og ca ma er a s suc asce membranes ( or examp e, p osp o p ds), aqueouspo ymer c DNA so u ons, some v ruses suc as e

obacco mosa c v rus, e so u on ex ruded by a sp der oorm s k reads, m ce es suc as soap so u on, co o da

so u ons, grap e and ce u ose amongs o ers. No e aqu d crys a ma er a s may no a ways be n e qu d

p ase jus as wa er s no a ways n e qu d p ase.

t p c p c chermotropic LC ma er a s are pure subs ances aoccur as LCs over a cer a n empera ure range be ween eso d and qu d p ases suc as e examp e o c o es eromyr s a e g ven prev ous y. A e empera ure be ow

e range, e subs ance orms a so d crys a ; above eempera ure range, urns n o e qu d p ase. he

b p eny n r es (cyanob p eny s) are common examp eso ermo rop c LCs, or examp e 5CB, w c s crys a nebe ow 18 C, an so rop c qu d above 36 C and LCbe ween e wo empera ures. See F gure 1424.

C5H11 C N

biphenyl

cyanogroup

Figure 1424 A thermotropic LC

Lyotropic LCs , on e o er and, are so u ons a s owe qu d crys a s a e a cer a n concen ra ons, a

a unc on o e concen ra on o e mo ecu es, sucsoap or de ergen , n a so ven suc as wa er ( n s cas

ead ng o e orma on o m ce es LC examp e). Aba cer a n soap concen ra on, a LC p ase s ormed nw c e e carbon c a n ydrop ob c a o e smo ecu es po n away rom e po ar wa er w e

ydrop c soap componen s po n oward e wa er.

hydrophilic, polarhead group

hydrophobic, non-polarhydrocarbon chain

H HO

H H O

H H

O

H H O

H H O

H HO

H H

O H H

O H

H O

H H

O

H H O

H H

O

H H O

H H

O

H H

O

H H

O

H H

O H H O

Figure 1425 A lyotropic LC

hermo rop c be av our n erms o arrangemen o mo ecu es n LC s a e:

In e crys a ne so d, e rod-s aped mo ecuare xed n pos on and d rec on: ese are paraarranged n ayers and e ayers pos oned one over eo er (as s own n F gure 1426) n a ree-d men ona

arrangemen . he n ermo ecu ar orces presen n a so da ce o a LC are d feren n var ous d rec ons. As

so d crys a s ea ed, rs e weak orces are overcome ea ng d s urbs e prec se order o mo ecu es g v

r se o random arrangemen n some d rec on, bu es ronger orces are s a p ay and s prov des reguarrangemen n o er d rec ons. Insmectic LCs , ayerss ex s ( e mo ecu es are s arranged n ayermovemen w n ayers so a e mo ecu es are rougpara e . See F gure 1426.

Fur er ea ng d srup s e ong range pos ona ordo ormnematic LCs n w c e ayer arrangemen

no onger ex s s. See F gure 1426. In nema c LCs, erod-s aped mo ecu es are d s r bu ed random y bu , onaverage, po n n e same d rec on; s s yp ca y

n LCDs. On s ur er ea ng, e ncreased eag a on d srup s s d rec ona order un s

e so rop c (norma ) qu d p ase s ormed w od rec ona order as we . I s e ab y o mo ecuLC o po n n a par cu ar ax s, ca ed e d rec or,

s d s ngu s ng ea ure:

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o P t i o n

P c p -c p

cA po ar zer a ows g n w c e e ec r c e d v bra es

n on y one d rec on o pass roug as s own n F gure1428 (a) and (b) a r g .

In crossed po ar zers, w ere one po ar zer s perpend cu aro e o er one n s d rec on o propaga on, no gransm ss on akes p ace ater e second po ar zer, as

s own n F gure 1429.

Lightvibratingin all directions

No transmissionof light

Figure 1429 The principle of cross-polarization

Lightvibrating

in all directions

Polarizer in the x direction

Polarizer in the z direction

Lightvibrating

in all directions

Light vibratingin only onedirection - x

Light vibratingin only one direction ( z ),

perpendicular to the x direction

a)

b)

Figure 1428 (a) and (b) The principle of a polarizer

Figure 1426 Order in crystals, smectic LC, nematic LC and isotropic liquids

Crystal Smectic LC Nematic LC Isotropic liquid

Crys a ne So d:g y ordered

L qu d Crys a Iso rop c L qu d:No ong rangeorderSmec c Nema c

Pos ona order Yes Some No No

D rec ona(or en a ona ) order

Yes Yes Yes No

Figure 1427 A comparison of LC forms for positional and directional order

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I , owever, a qu d crys a s p aced be ween e abovewo crossed po ar zers, ransm ss on o g can occur

ater e second po ar zer as s own n F gure 1430.

h s sugges s a a LC s ab e o ro a e or w s e p ane o

po ar za on o e g propaga ng roug . As s a edear er, s e ab y o mo ecu es n a LC o po n na par cu ar ax s, s d rec or, a a ows LC mo ecu es

o ransm g depend ng on e or en a on o emo ecu es. he or en a on o e po ar LC mo ecu es canbe con ro ed by e app ca on o a sma vo age across a

n m o e ma er a . he areas o e d sp ay a areg and dark can be con ro ed n s way.

LCDs use very e e ec r ca power and are us deaor use n ba ery opera ed e ec ron c dev ces suc as

ca cu a ors, rad os, d g a wa c es, ap op no ebooks,mob e p ones, la pane d sp ays (LCD TVs), e c. ead ng

o a mu -b on do ar ndus ry.

Proper es needed or a subs ance o be used n qu d-crys a d sp ays:

he ear es LC ma er a s, e cyanob p eny s were oundo be dea or use n LCDs because ese mo ecu es possess

a number o mpor an proper es: he r c em ca s ab y means ey do no decompose n e ns rumen s; ey areopera ona a room empera ure and e LC p ase s s ab eover a w de and su ab e empera ure range ( or examp e,

rom abou 10 C o 60 C). Add ona y, e ma er a save d po es (po ar or eas y po ar zab e). h s s essen a

as e app ca on o an e ec r ca e d eads o a c ange ne or en a on o e mo ecu es. A so, LCs mus ave a

rap d sw c ng speed be ween or en a ons so ere s noag w en a sma vo age s app ed, a s, ey mus ave

a as response me o e app ed e ec r c e d.

Lightvibrating

in all directions

Liquidcrystal

Figure 1430 The use of an LC with a polarizer

Nano ec no ogy as g ven us e oo s o p ay we u ma e oy box o na ure a oms and mo ecu

Every ng s made rom he poss b es o crenew ngs appear m ess.

Hors S ormer (Nobe aurea e)

Figure 1431 Atomic art?

F gure 1431 s ows e Japanese Kanj , w c means a om,wr en era y w a oms, eac jus a ew nanomacross.

C7nanoteChnology

C.7.1 Deine the term nanotechnology.

C.7.2 D st ngu sh between phys cal andchem cal techn ques n man pulat ngatoms to orm molecules.

C.7.3 Descr be the structure and propert es o carbon nanotubes.

C.7.4 D scuss some o the mpl cat ons o nanotechnology.

IBO 2007

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o P t i o n

Nano ec no ogy nvo ves measuremen s n e nanome resca e, name y 1012 m range w c s e s ze o a group o a oms; DNA mo ecu es are abou 2.5 nm w de, e sma esbac er um s abou 200 nm w de w ereas uman a r sabou 100,000 nm w de.Nanoparticles oten ave p ys caand c em ca proper es a are qu e d feren and nove

s nce a arge propor on o e sma group o a oms are ae sur ace, a s ey ave a arge sur ace area o vo ume

ra o compared o bu k ma er. For examp e, go d s knownor s c em ca ner ness. However, a e nanosca e s

reac ve, ca a y c and s me ng po n s muc ower ( nac a qu d a abou room empera ure) compared o e

macrosca e e emen . Par c es o go d can a so appear red,b ue or go d, depend ng on e r s ze. hus a nanosca e,proper es do no depend on y on compos on ands ruc ure o e ma er as ey do a e macrosca e.

Dein t on of the term nanotechnology: Nano ec no ogy nvo ves researc and ec no ogy deve opmen a e

1 nm o 100 nm range. (I ) crea es and uses s ruc uresa ave nove proper es because o e r sma s ze.

Nano ec no ogy bu ds on e ab y o con ro orman pu a e a e a om c sca e.

(De n on rom IBO Gu de as quo ed rom eNano ec no ogy In a ve.)

C.7.2 D st ngu sh between phys cal andchem cal techn ques n man pulat ngatoms to orm molecules.

IBO 2007

Scann ng probe m croscopes (suc as e scann ngunne ng m croscopes, STMs) are ab e o move nd v dua

a oms one a om a a me, or a ow e con ro eddepos on o s ng e a om c or mo ecu ar ayers one on

op o ano er. Me a s can be vapor zed and a om c ayerdepos on eads o nanopar c es w en coo ed. hese areexamp es o p ys ca ec n ques w c a ow a oms obe man pu a ed and pos oned o spec c requ remen s.On e o er and, c em ca ec n ques pos on a oms

n mo ecu es us ng c em ca reac ons. hus w ereas aSTM can be used o move a carbon monox de mo ecu e

o an ron a om, a vo age can be used o c em ca y b ndese oge er. S m ar y, a vo age ac va ed p a nu

r od um p on a STM can ca a yse e omo y c ss ono ydrogen gas and depos e ydrogen a oms across aC=C a kene doub e bond p aced on a sur ace. he resu sse ec ve ydrogena on o e doub e bond.

C.7.3 Descr be the structure and propert es o carbon nanotubes.

IBO 2007

A carbon nano ube (CNT) s made o ro ed grap e(grap ene) a ong an ax s cons s ng o carbon exagons

and c osed a e ends by em sp er ca ( a -s ze)u erene- ke caps or domes requ r ng carbon pen agonso c ose e s ruc ure a e ends. Nano ubes are o ow

cy nders made o carbon a oms and can be one a omck (s ng e-wa carbon nano ubes - yp ca y abou

1 nm w de, bu w der ones can be ormed) or mu -wa edcarbon nano ubes cons s ng o concen r c nano ubesw a sma er one n a arger one, ke a se o Russ anma ryos ka do s. Typ ca y e s des o e ubes con a

exagons, e caps exagons and pen agons. he a erare ra er more suscep b e o c em ca reac ons and ereac v y a ows par c es o me a s, me a ox des, msa s amongs o ers o be nser ed n o e nano ubes.F gure 1432 s ows a s ng e-wa ed carbon nano ube

Figure 1432 A single-walled carbon nanotube

he s ruc ure o a nano ube de erm nes s proper es sucas e ec r ca and erma conduc v y. W ereas grap e

TOK Does technology blur the d st nct onbetween s mulat on and real ty?

The scann ng tunnell ng m croscope turns electr cals gnals generated as the probe turns over the sample

nto an mage. Does the way t does th s vary rommach ne to mach ne? In other words do d ferentmach nes g ve the same mage? Even the answer syes then surely the s gnals are turned nto an mageaccord ng to some model s th s real ty? I not thenI suppose we could ask wh ch mage s the correct

mage? There are almost certa nly eatures they haven common, l ke the arrangement and spac ng o the

atoms, but th s at present only re n orces data wehave rom other techn ques such as X-ray d fract on,us ng wh ch we have been able to construct 3Dmodels. So does be ng able to see atoms actuallymake us more certa n o the atom c model, because

t allows a s mulated d rect v sual d splay? Comparedto other th ngs the efect o the scann ng tunnell ngm croscope on blurr ng s mulat on and real ty sprobably pretty tr v al. What do you th nk?

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sot and somew a ma eab e, CNTs are s ruc ura y r g dand ex reme y s rong, many mes s ronger an s ee . L kegrap e, carbon a oms are bonded by s rong cova enbonds w sp2 ybr d za on a ong e nano ube eng .hey a so ex b un que e ec r ca proper es, and can ace er as exce en e ec r ca conduc ors or sem conduc orsdepend ng on e eng and mu -wa s presen . henarrower e d ame er o e nano ube, e ess be aves

ke grap e. As e d ame er ge s w der, e more s bu kproper es are s m ar o ose o grap e; s s yp ca o

e nanosca e ma er a s men oned ear er.

C.7.4 D scuss some o the mpl cat ons o nanotechnology.

IBO 2007

P b pp c

Curren app ca ons nc ude nv s b e suncreens compr s ngan um or z nc ox des, bac er oc da bandages w s vernanopar c es, produc on o sp -proo , wa er repe enand wr nk e ree garmen s (requ r ng n requen co dwa er c ean ng), e erogeneous ca a ys s and m croc rcu s,amongs many o ers. Progress n nano ec no ogy researc and deve opmen s rap d as governmen s,researc ns u ons and ndus ry are nves ng eav y n

. Po en a uses range rom deve opmen o vacc nes anddrugs o as er, c eaper and more power u e ec ron csw muc g er s orage capac es, o g we g ,

onger as ng ma er a s or cons ruc on, ranspor a onand everyday uses a requ re ess energy and resources

and cause ess po u on.

Nanomed c ne and b onano ec no ogy are examp es o new mu d sc p nary e ds w deve opmen s n, orexamp e, drug de very me ods. I drugs can be arge ed jus o cancer ce s n e correc dosage, e bene wou dbe remendous o soc e y n erms o reduced cos s and

ewer poss b e s de efec s. S m ar y e poss b y o us ng nano-amoun s as ca a ys s n ca a y c conver ers,

ue ce s, o re ner es and c em ca ndus r es can go aong way o reduc ng po u on. Incred b e poss b es are

be ng sugges ed or nano ec no ogy no doub w eado beau u successes and spec acu ar a ures. I cer a n y as ead o Nano-Buzz and Nano-Hype.

h f c c cI s poss b e a e comb na on o sma s ze andd s nc ve proper es may pose env ronmen a and or

ea r sks. he sma s ze means s easy o n a enanopar c es. For examp e, e u ra n soo par c es

rom ndus r a ac v y are known o ave adverseefec s on e resp ra ory sys em o umans. W a abouposs b e cancer caus ng r sks nanopar c es can c ange

e gene c makeup o ce s? W nanopar c es be o cross e b ood-bra n barr er and ey can, w a

w e efec s be? W a abou e use o me a oxnanopar c es n sunscreens, s ere any po en a azaas a resu o absorp on roug e sk n? Nanopar c

ave been ound o be arm u o an ma s. I ese caen er e ymp a c sys em, e bodys mmune sys em, pass ng roug e sk ns op ayer, ere cou d be eaconcerns.

t c c che e d o nanotoxicology s concerned w var ousapsec s o e ox c y o nanopar c es, s nce ma er a s ave proper es qu e d feren rom e r maccoun erpar s. For examp e, an ner ma er a may become very reac ve a e nanosca e and e curren s andardo ox c y or a subs ance may no onger app y. hus de erm na on o e arm u efec s o nanopar c es

umans and e env ronmen presen s a grea c a enge

s nce ere are many var ab es nvo ved suc a s ze, s apesur ace area o vo ume ra o e c. Nanopar c es end aggrega e and e proper es o ese nanoc us ers end

o be d feren rom nanopar c es, ur er comp caox c y ssues. he webs e www.nano ox c y.p p mak

severa re erences o e ox c y o nano ubes and s an area a requ res more researc and da a n ordero es ab s ox c y s andards. As more da a s ava

nano ec no ogy w requ re n erna ona regu aand res r c ons on e produc on and use o arm uproduc s.

r p b

I nano ec no ogy does no requ re eavy ndus ry,scarce na ura resources and mass ve cap a , as po en a or exponen a grow o manu ac ursys ems ead ng o as acce era on n manu ac ure a

mprovemen o produc s and use o nexpens ve rawma er a s (as muc sma er amoun s w be requ red). herespons b y o ndus r es o r se o e c a engesby nano ec no og es w requ re work ng o e ge ca and soc a s andards w e ba anc ng be wg oba and se n eres .

e c p c he mp ca ons o nano ec no ogy are many and ese

ave g ven r se o new n erd sc p nary areas o s urang ng rom nanoe cs ( e e ca and soc a uses deve op ng nano ec no ogy, or examp e e m ary usuc as c eaper, more power u weapons) o nanopo cs,(suc as e need or pub c educa on, or n ormedeba e and or pub c nvo vemen n po cy d scuss ohe nano-d v de s e concern o e ncrease n e gapbe ween e poor and e r c ; cou d nano ec no ogy

e p reduce e d v de by mak ng sma er and c eaperec no ogy ava ab e o a arger number o peop e aroun

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o P t i o n

e wor d? Nano ec no ogy s s a an ear y s age ande sc ence be nd s no u y unders ood. I s o

g oba mpor ance and success u use o nano ec no ogy or e bene o umans w requ re a jo n efor by

governmen s, ndus ry, academ a and bus nesses romaround e wor d.

Can anyth ng ever be values ree? As humans wenev tably have values and cannot help regard ng

everyth ng n the l ght o these values. These valueso course are the undamentals o moral judgementsand d fer rom person to person. There are var ousmoral codes such as Ut l tar an sm, M ght s r ght,Do unto others as you would have them do to you,

Cultural relat v sm.

I suppose, pragmat cally, the bas c pr nc ple gu d ngresearch has to be He who pays the p per calls thetune. I you dont want any money to do t, then youcan probably research nto what you l ke as long as

ts legal. Aga n I dont th nk there s much quest onabout th s w th regard to pr vate research nst tut ons;

ICI s pay ng or the research then nobody quest onsthem tell ng the r sc ent sts what to nvest gate. W thresearch that takes place n state nst tut ons then t snot qu te clear who s pay ng the p per. Somet mes

ndustr al compan es w ll sponsor a research worker

and aga n probably they have the r ght to d rect thatresearch, but what about the others? Maybe thereshouldnt be any others, maybe those who are l kelyto proit should pay l ke ndustry does, but who thenwould be l kely to proit? In the short term, shall wepay or better mapp ng o the Earths magnet c ield byan expens ve satell te? It m ght never get done eventhough n the long term there could be lots o beneits,generally mposs ble to pred ct at the outset. The laser

s a good example o a d scovery that has trans ormedso many th ngs and wh ch came out o some

blue sky research. I suspect we (at least you are ataxpayer) are the payers. Maybe I have 10 m nuteso a sc ent sts t me as a result o what I pay n taxes I wonder what Im go ng to get h m/her to do? Nota problem, the government, n ts w sdom, as wellas tak ng our money away rom us n taxes because

t knows better how to spend t, also rel eves us

o the burden o research dec s ons. Once upon at me academ cs were trusted just to research ntowhatever they ound nterest ng. Nowadays money

s a l ttle t ghter, so that usually they have to subm tproposals to research counc ls who award und ng.Un ortunately that means that many spend as mucht me wr t ng research proposals and go ng through allthe nvolved ollow up, as they do actually carry ngout any research! Who are on these research counc lsanyway? Usually t s other sc ent sts n a s m larield who, supposedly, have the expert se to dec dewh ch projects deserve support and wh ch do not.But what should the r dec s ons rest on someth ng

that looks l kely to pay of n 5-years or someth ngthat, just poss bly, m ght revolut on se everyth ng 50years down the track? Somebody who s work ng n aprest g ous un vers ty, somebody who has publ sheda lot o academ c papers (though maybe o dub ous

nterest) recently, the guy who bought you a beer nthe bar at the last con erence? Lack o und ng m ghteven be a st mulus; I th nk t was Ernest Ruther ordwho sa d Our request or und ng hasnt beengranted, so well have to th nk nstead.

TOK Sc ence versus Pol t cs

W p c ?

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h gher level

here are wo ma n ypes o po ymers add on andcondensa on po ymers.

In addition polymerization , monomers are unsa ura edorgan c compounds suc as e ene, CH2= CH2 andc oroe ene CH2=CHC (v ny c or de). Monomerun s add oge er w ou e e m na on o any a oms o

orm e po ymer. Add on akes p ace across e doub ebond. Ater po ymer za on, e doub e bond s conver ed

o a s ng e bond. Typ ca y, a s ng e monomer s nvo ved(see a so C.3)

In condensation polymerization , e monomer un save wo reac ng s es on em or po ymer za on o ake

p ace suc as d carboxy c ac ds, d o s and d am nes (ca edb unc ona monomers). hese undergo condensa onreac ons o produce a arger mo ecu e w ee m na on o a sma er mo ecu e suc as wa er. Typ ca y

wo monomers are nvo ved, oug ere are examp eso condensa on po ymers (suc as ny on-6) w c on y

nvo ve a s ng e monomer w d feren unc ona groupsa e wo ends o . Bu aned o c ac d, e ane-1,2-d oand 1,2-d am noe ane are examp es o b unc onamonomers as s own n F gure 1433.

Butanedioic acid

Ethane-1,2-diol

1,2-diaminoethane

C CH 2 CH 2 C

O

OHHO

O

HO CH 2 CH 2 OH

N CH 2 CH 2 N

H

HH

H

Figure 1433 Examples of bi-functional monomers

hus, e repea ng un o e po ymer made rom econdensa on o e wo monomers bu aned o c ac d ande ane-1,2-d o s s own n F gure 1434.

CC

O

O

CH 2CH 2

O

O CH 2CH 2n

[ [From butanedioic acid From ethane-1,2-diolFigure 1434 The repeating unit

examPles o Condensat on PolymersP - p che OH group on e p eno s 2,4-d rec ng. hus,

e n a reac on be ween p eno and me ana nvosubs u on a bo e 2- and 4-pos ons on e benzr ng as s own n F gure 1435.

C8 Condensat onPolymers (hl)

C.8.1 D st ngu sh between addition andcondensation polymers n terms o the rstructures.

C.8.2 Descr be how condensat on polymers areormed rom the r monomers.

C.8.3 Descr be and expla n how the propert eso polymers depend on the r structural

eatures.

C.8.4 Descr be ways o mod y ng thepropert es o polymers.

C.8.5 D scuss the advantages andd sadvantages o polymer use.

IBO 2007

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o P t i o n

O H

HCHO

OH

CH 2OH

OH

CH 2OH

+ 22

+

Figure 1435

I s e reac on o e subs u ed produc s rom e abovereac on w p eno a undergo condensa on w ee m na on o wa er, as s own n F gure 1436.

CH 2 OH

OH OH

H

OH OH

CH2

OH2

+

+

Figure 1436

Subsequen condensa on reac ons w ydrogen on e2- and 4-pos ons produce e p eno -me ana p as c(commerc a y ca ed Bake e) w ex ens ve cross- nks.As s own n F gure 1437.

OH

CH 2

CH 2

OH

CH 2

OH

CH 2

OHOH

CH 2

OH

CH 2

Figure 1437 Structure of bakelite

PPo yure anes are used ex ens ve y n mak ng po yure ane

bres and oams. Po yure ane s made by e reac on o d -socyana es n w c an oxygen a om s bonded o e cyano

group a e er end o e carbon c a n con a n ng monomer:OCN(carbon c a n)NCO. he o er b unc onamonomer or e condensa on reac on s a d o , or examp e,e ane-1,2-d o as s own n F gure 1438 (a).

P p PetPET s e po ymer o c o ce n e b ow-mou ded bo n

ndus ry because un ke g ass s g we g and does ns a er. I s a po yes er made by e condensa on o benzene-1,4-d carboxy c ac d (ca ed erep a c ac d) w e a1,2-d o (ca ed e y ene g yco ) ence e name o epo ymer: po ye y ene erep a a e, PET. (F gure 1438 (b)).

aCtors determ n ng the ProPert es o Condensat on PolymersC he grea er e ave

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