To keep it as simple as possible, (K.I.S.S.) this topic...

keep it simple science TM

www.keepitsimplescience.com.au

Emmaus Catholic College SL#802440

1

but first, an introduction...

HSC Chemistry Topic 1

PRODUCTION of MATERIALSWhat is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. POLYMERS FROM PETROCHEMICALS & BIOMASS

2. ALTERNATIVE FUELS - ETHANOL & THE ALKANOLS3. REDOX CHEMISTRY & BATTERIES

4. RADIOACTIVITY & ITS USES...all in the context of society�’s use of energy and materials

In the previous topic in the Preliminary Course, you learntabout carbon chemistryand the importance of petroleum as a fuel source.

This topic begins by taking this idea further. Petroleum notonly provides fuels, but is a source of chemicals for makingplastics.

To understand this, you need to learn about a vital chemicalEthylene, and the important industrial process of

Polymerization.You will learn about natural polymers, too. All living thingsare built from polymers, and as the Petrochemicals runout, we need to look to living things to provide our rawmaterials in the future.

plastics

Then you will learn more carbon chemistry when you studythe alcoholsand the most important member of this group

ETHANOLa possible candidate for replacing petrol as a fuel.

Then onto REDOX Chemistry,

Finally, we go into the atomic nucleus to study thephenomenon of Radioactivity

+ nn +

!!

C2H5OH

and its involvement

in electric

Cells &

BatteriesPhoto by Marcel Hol

HSC Chemistry Topic 1Copyright © 2005-2007 keep it simple science


www.keepitsimplescience.com.auHSC Chemistry Topic 1Copyright © 2005-2007 keep it simple science


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Isotopes

Addition Polymers

PolyethylenePVC

Polystyrene

Ethylene;Chemistry

&Sources

Condensation Polymers

Conversion of Ethylene to/from Ethanol

Ethanolfrom

Fermentation

RadioactivityAlphaBeta

Gamma

TransuranicElements

Production & Uses ofCommercial

Radioisotopes

GalvanicCells.

Structure&

Chemistry

Displacement Reactions&

Activity Series of the Metals

Biopolymers

The Potential ofCellulose

Combustionof Alkanols

Heat ofCombustion

Assessment ofEthanolas an

Alternative Fuel

Standard ElectrodePotentials & Cell

EMF

Oxidation StatesOxidation Number

CommercialCells &

Batteries

The Alkanols.Structure

&Properties

PPRROODDUUCCTTIIOONNooff

MMAATTEERRIIAALLSS

Polymersfrom Petrochemicals

&Biomass

Alternative Fuels.Ethanol &

the Alcohols

REDOXChemistry

&BatteriesRadioactivity

& its Uses

CONCEPT DIAGRAM (�“Mind Map�”) OF TOPICSome students find that memorizing the OUTLINE of a topic helps them learn and remember the concepts andimportant facts. As you proceed through the topic, come back to this page regularly to see how each bit fits thewhole. At the end of the notes you will find a blank version of this �“Mind Map�” to practise on.

Oxidation&

Reduction

PetrochemicalsWhen petroleum is refined, the major products are thefuels such as petrol and diesel. However, its not all aboutfuels. Our chemical industry depends on a whole range ofother compounds extracted from petroleum, which arecollectively called �“Petrochemicals�”.

Petrochemicals are vital raw materials for the manufacture of�• plastics and synthetic fibres�• pigments for inks, dyes and paints�• detergents & adhesives�• cosmetics & pharmaceuticals�• explosives

... and much more.

One of the most important petrochemicals is

Ethene (Ethylene) C2H4Ethene is also known by its common name, �“Ethylene�”.This is the name favoured in the syllabus, so it will be used from here on.

Ethylene is the simplest of the Alkene homologous series.You previously learnt about the Physical Properties of thealkenes:

�• low m.p. & b.p.�’s. Due to non-polar bonding�• insoluble in water. within, there are only weak�• non-conductors �“Dispersion Forces�” between

of electricity. the molecules

The only Chemical Property you know about so far is thatalkanes and alkenes will undergo combustion... they burn.Now you�’ll find out more...

Chemistry of EthyleneThe reason that ethylene is one of the most usefulchemicals on the planet is all about that double C=C bond.

Addition Reactions of EthyleneThese are not required learning, but study each diagram tomake sure you understand the concept of an �“AdditionReaction�” across the double bond

Reaction with Hydrogen

+ H2

Ethylene + Hydrogen Ethane

Reaction with Bromine

+ Br2

Ethylene + Bromine 1,2-dibromoethane

Reaction with HCl

+ HCl

Ethylene + Hydrogen Chloride Chloroethane

Reaction with Water

+ H2O

Ethylene + Water Ethanol

These are just a few of the possible Addition Reactionsthat can occur across the double bond

3


1. POLYMERS FROM PETROCHEMICALS & BIOMASS




H H

HH

C C

HHH

HC C

H

HH

HC C

X Y

XYY

The doublebond is highlyreactive

It readily �“splits open�”leaving a single C-CCbond, and creating 2new bond positions forother atoms/groups toattach to the molecule

THIS IS CALLED AN�“ADDITIONREACTION�”

H H

HHC C

H H

HHC C

H H

HHC C

H H

HHC C

H HHH

C C

H H

H HHH

C C

Br Br

H HHH

C C

H OH

H HHH

C C

H Cl

Ethylene C2H4is the simplest, and most important

of the Alkenes.

It is one of the most important Petrochemicalsbecause of the variety of products

that can be made from it.

Its chemical versatility is due to the double C=C bond

which is highly reactiveand allows many �“Addition Reactions�”

to occur.




4

The Industrial Source of EthyleneCrude petroleum contains very little ethylene. When the�“fractions�” are separated by Fractional Distillation, there isa large fraction of low-value alkanes with 15 or morecarbon atoms.

e.g. pentadecane C15H32

These large molecules are broken into smaller molecules bya process called �“Cracking�”, which can be done by simplyheating (�“Thermal Cracking�”) or by the use of a Zeolitecatalyst... �“Cat Cracking�”.

When the molecule is broken into fragments, some piecesform as alkanes, but others must form as alkenes, becausethere are no extra atoms to occupy the bond positions thatare created.

Once �“cracked�”, the mixture is fed back into the FractionalDistillation process. Many of the smaller molecules end upin the valuable petrol or diesel fractions.

Any ethylene formed is recovered from the gas fraction.

Practical WorkIdentifying Alkenes with BromineYou may have done simple experiments to learn how analkene can be quickly and easily identified, anddifferentiated from an alkane.

A water solution of bromine (Br2(aq)) has a brown colour.

If it is in contact with a liquid hydrocarbon, the water andthe hydrocarbon form separate layers... they are immiscibleliquids. Water, being denser, will always be at the bottom.

Bromine is actually more soluble in a hydrocarbon, sowhen shaken, it will switch to the top hydrocarbon layer,and changes colour from brown to purple.

In an alkane (hexane is often used) the colour will changeand switch layers, but it will remain coloured because noreaction occurs.

In an alkene (e.g. hexene) the bromine totally loses allcolour because an addition reaction occurs.

Before Shaking

Hexene layer

Brown �“Bromine Water�”layer

After Shaking

Clear Hexene layer

Clear water layer

The bromine isdiscoloured by anyalkene.

The Reaction of Bromine with Hexene

+ Br2

Hexene Bromine 1,2-dibromohexane

H

HHC C

H H H

HHH

C C CH

HC H H

BrBr

HH

C CH H H

HHH

C C CH

HC H

H

HC

H H H

HHH

C C CH

HC

H

H

CH H H

HHH

C C CH

HC H

H

H

H CH H H

HHH

C C CH

HC

H

HC

H HH

HH

C C

H

HC

H H

HHH

C C C

H

H

C H

H

H

H CH H H

HHH

C C CH

HC

H H

HHC C

�“Cracking�”

If you add up all the atomsin these 3 productmolecules, you�’ll see thatthe total is the same

Ethylene, C22H44

Pentene, C55H1100Octane, C88H1188

Ethyleneis obtained from the

�“Cracking�”of long-chain petroleum fractions



5

PolymersOne general category of chemicals are known as�“Polymers�”. All polymers are large molecules made byjoining together many small molecules, called monomers.(�“poly�” = many, �“mono�” = one, �“mer�” = unit)

Many of the important molecules in living cells arepolymers, for example:

�• starch is a polymer of many glucose molecules.�• proteins are polymers of amino acids.�• DNA is a polymer of nucleotides, sugar and phosphate.

Many common, widely used substances are manufacturedpolymers, including all the different plastics and syntheticfibres such as nylon.

Ethylene is the starting chemical (�“feedstock�”) in themanufacture of many polymers.

Addition Polymerization of EthyleneNot only can ethylene carry out addition reactions withbromine, water, etc., but many ethylene molecules can reactwith each other.

You may have used molecular models to help visualize theprocess.

The result is that the ethylene monomers join together byaddition reactions across the double bond. This is an�“Addition Polymerization�” process and results in apolymer called �“Polyethylene�”, also known by the tradename �“Polythene�”

Industrial Production of PolyethyleneMore Polyethylene is manufactured than all other plasticsput together... it is one of the most used materials in ourworld. There are basically 2 different production methods,which produce 2 different forms of polyethylene.

Low Density PolyethyleneIf the monomer ethylene is treated with�• high pressure (over 1,000 atmospheres)�• high temperature (300oC)�• an �“initiator�” chemical

addition polymerization occurs, with about 2,000monomers joining to form each �“super-molecule�” ofpolymer. In this case, the initiator chemical also causes thepolymer molecules to have side-branches.

These molecules cannot packtogether closely, so the plastic

is low-density, highlyflexible, soft and clear...

CCCCllll iiiinnnngggg--WWWWrrrraaaapppp FFFFiiii llllmmmm&&&& PPPPllll aaaassss tttt iiii cccc BBBBaaaa gggg ssss ....

High Density Polyethyleneis manufactured �• at lower pressure (2-3 atmospheres)�• at lower temperature (about 60oC)�• with a complex catalyst

This time there are no side-branches. The long polymermolecules can pack together forming a higher-density,harder plastic used for toys, plastic utensils, and the tough,�“crinkly�” carry bags from shops.

As with all materials, the uses of these plastics is closelylinked to the properties they have, and their properties arecontrolled by their chemical and molecular structure andbonding.

This idea is taken further on the next page.



Addition Polymerization is anAddition Reaction across a double C=C bond

which joins monomers to make a polymer.

Polymers can be named by adding �“poly-�”as a prefix to the monomer name.

CH22=CH22 CH22=CH22 CH22=CH22

Condensed Structural Formula (-CCH22-CCH22-))nn



6

Other Important Addition PolymersThe compound chloroethene is an ethylene molecule withone hydrogen atom replaced by a chlorine.

Chloroetheneis also known by its common name �“vinyl chloride�”

Since this molecule contains a double bond, it can undergoaddition polymerization to form �“Poly Vinyl Chloride�” orP.V.C.

(-CH2-CHCl-)n

If one of the hydrogen atoms of an ethylene molecule isreplaced by the ring-shaped �“benzene�” group, thecompound has the technical name �“ethenylbenzene�”, but iscommonly known as �“styrene�”.

If this undergoes addition polymerization, the polymer is�“polystyrene�”, so familiar in insulation, hot-drink cups,bean-bag filling, etc.

Polystyrene (-CH2-CH(C6H5)-)n

Systematic Common PolymerName of Name of Name(s)Monomer Monomer

ethene ethylene PolyethylenePolyethenePolythene

chloroethene vinyl chloride P.V.C.polyvinylchloridepolychloroethene

ethenylbenzene styrene polystyrenepolyethenylbenzene

Uses, Properties & StructureThe molecular structure and bonding of each plasticdetermines its properties, and the properties determinewhat uses the material is best suited for.

To keep it simple (K.I.S.S. Principle) consider just the 3plastics above, and consider just their hardness and rigidity.

In low-density polyethylene, the molecules are long, non-polar, branched chains (diagram previous page). Being non-polar (so only weak dispersion forces operate) and unableto get close together, each molecule can bend and twisteasily.

So, the plastic is soft and very flexible. It is perfect for cling-wrap film, sandwich bags and as the plastic lining in milk orjuice cartons.

In P.V.C., the chlorine atoms more than double the mass ofeach molecule. Since dispersion forces increase withmolecular weight, it means that the polymer moleculesattract each other more strongly. Each molecule is held inplace more, so the entire substance is harder and lessflexible.

P.V.C. is a tougher, more rigid plastic. This makes it ideal fordrainage pipes, guttering and electrical conduit pipes.

In polystyrene, the compact benzene side group is almosttwice the mass of a chlorine atom, so the molecules areeven heavier and dispersion forces stronger. Polystyrene isa hard, tough, rigid plastic, often used for making handlesfor cookware and hand-tools such as hammers or chisels.

Note that the more familiar use of polystyrene is in light-weight �“foam-plastic�” for insulation, hot-cups andpackaging. In this form it has been injected with gas tomake very light, fluffy granules. The plastic itself is hardand rigid.



H H

ClHC C

H

Cl

CH H

ClH

C CH

HC

H H H

ClHCl

C C CH

HC

H H

H

H H

HH

HC C

C

C

C

C

C

C

H H

HC C

H H

HC C

H H

HC C

H H

HC C

H H

HC C

H H

HC C

Benzene ring

This is commonlyabbreviated as

The Syllabus Requires that you know both the

Systematic and Common Namesfor these important monomers

A summary follows

Bonding & Properties UsesStructure



7

Condensation PolymersThere is another way that polymers can form.For example;the monomer �“6-aminohexanoic acid�” has the structure

This can be abbreviated as

Two of these molecules can join together as follows

The result is:

Since a molecule of water is formed each time 2 monomerscombine, this reaction is called �“Condensation�”. Eachmolecule can join to another at each end, so manymonomers can join in long chains... a polymer is formed.

The example above results in the polymer we call �“Nylon�”,widely used in fabrics and clothing.

As well as nylon, other common condensationpolymers are polyester (fabrics) and P.E.T. (drink bottles).

ALL BIOLOGICAL POLYMERS, such as proteinsand starch, ARE CONDENSATION POLYMERS.

When the Petrochemicals Run OutPetroleum is a non-renewable, fossil fuel. The estimates are thatit will last only about 30 years at current usage rates. Whensupplies begin to run short, (this may already be happening) wewill not only face a shortage of fuel, but of vital chemicals forour manufacturing industries.

Ethylene is an example of a critical petrochemical. It is oneof the raw �“feedstock�” chemicals for making plastics,fibres and fabrics, medicines, dyes and pigments for ink andpaint, cosmetics, detergents, and much more.

Eventually, and maybe sooner than we realize, we will needto find new raw material resources to replace the dwindlingoil supplies. It makes sense that the new sources arerenewable and sustainable, so that we can manufacturethe things we need far into the future.

For renewable and sustainable, we must use living thingsand their products...

CelluloseYou may be aware that all plant cells are surrounded by arigid cell wall which supports, protects and strengthensplant tissue. The plant cell wall is made of cellulose.

Cellulose is a condensation polymer. The monomer isglucose, the sugar made by plants during photosynthesis.

When glucose molecules join together, each pair eliminatesa water molecule... a condensation reaction. To makecellulose, thousands of glucose molecules join intointerlocking chains.

You are familiar with cellulose... it is the fibrous stuff ofcotton and linen. We make enormous use of it as paper. Wealso waste a lot of it in the plant husks, leaves, stalks andstubble left over from our crop growing and timberindustries. Could it be better used?



H

HC

H O-HH

OH

C CHH H

HHH

N C CH

HC

O-HH

O

CH

H

N (CH2)5

O

CH

H

N (CH2)5

O-HH

O

CH N (CH2)5

NH22�“amino�”group

COOHacidgroup

O-HH

O

CH

H

N (CH2)5O-HHO

CH HN (CH2)5

O-HH

H

These atoms formwater, H22O

and the molecules jointogether at the vacantbond positions

+

Condensation Polymersare formed when monomer molecules

join togetherby eliminating a molecule of

WATER



8

Cellulose as a Future Raw MaterialThe glucose molecule CAN be used to replace manypetrochemicals.

Simple, existing technology allows:

Unfortunately, we have not yet developed a simple,efficient and economical way to break the cellulosepolymer down into molecules of glucose.

We can make ethanol and ethylene on a large scale fromstarch or sugar, but real sustainability will come by beingable to use the cellulose in all the �“waste�” plant matter.

BiopolymersThe word �“Biopolymer�” refers to those naturally occurringpolymers made by living things, such as starch andcellulose. Humans have always used these polymers (e.g.using cotton for clothing) and for nearly 100 years havebeen using chemically modified versions of them. Forexample, �“rayon�” is a synthetic fibre made from modifiedcellulose.

Research has been going on for many years on ways to getliving things to make polymers with properties more likethose of the useful petrochemical-based plastics.

A lot of the research has centred around the polymer�“polyhydroxybutyrate�” (PHB) which has properties nottoo different from polyethylene. It was discovered 80 yearsago that PHB can be made by bacteria, such as the speciesBacillus magaterium.

In recent years, the Monsanto company has used GeneticEngineering (G.E.) to transfer the genes for PHBproduction into corn plants. The crop is grown, harvestedand eaten as usual, but then the stalks and leaves areharvested for their PHB content, which is as high as 20%of the dry weight.

Analysis�• PHB has properties which make it suitable to replacesome plastics for packaging, but it tends to be brittle, andextra breakages must be accepted.�• PHB has the major advantage of being biodegradable, butthis also limits its range of uses, since it can rot anddisintegrate during use.�• There is resistance from farmers and consumers regardingthe use of G.E. plants.�• The production of PHB is not yet as cheap as usingpetrochemical plastics.

Conclusion: PHB grown in corn has potential, but isunlikely to become widely used yet.



Glucose

Ethanol

Fermentation will be studied in the next section

Can be used as a fuel

Chemical Processing

Feedstock forPlastics & othermanufacturing

Photo by Maciej Ciupa

Photo by Luis Rock

Ethylene

Worksheet 1

Fill in the Blank Spaces

When petroleum is refined the main products area)................................, but there are also other chemicalsextracted for use in manufacturing. These chemicals arecollectively called �“b)............................................................�”and the most important is c)..................................................

The reason for ethylene�’s great usefulness is the d).................carbon-carbon bond. This bond is highly e)...........................and readily �“splits open�” allowing other atoms/groups tojoin onto the molecule. This is called an f)...............................Reaction.

In the laboratory, compounds containing a double bondcan be identified using a solution of g)...................................If this is added to an alkene, the g)................................... willbe h)............................................. because of an additionreaction. With an alkane, the colour may change and shiftfrom one solvent to the other, but will not be h)....................

The yield of Ethylene from petroleum is greatly increasedby the process of �“i)............................................�” in whichlong-chain alkanes are broken into smaller fragments byeither j).................................. or ........................................ Thisincreases the yield of valuable fuel fractions such ask)....................................... and increases the yield of ethylenewhich is extracted from the l).......................... fraction.

The major use of ethylene is the manufacture ofm)............................................... Thousands of ethylenemonomers join together by n).................................. reactionsto form o)........................................................... If the reactionis carried out at high p).......................... and .............................with an �“initiator�” chemical, the result is q)...................-density polyethylene. The long chain molecules have manyr).......................................... and cannot pack close together,so the plastic is soft and s)........................................, ideal forsoft plastic bags and t)............................................... film.

If the reaction is carried out at lower pressure andtemperature with a u)................................................., thepolymer molecules lack branches and can v).............................................................. to form w)......................-densitypolyethylene, used (for example) in �“crinckly�” x)...................................................... from shops.

Other important polymers are:�• P.V.C. which stands for y).......................................................The monomer is commonly called z).......................................,but its correct chemical name is aa)...........................................The added chlorine atom makes the molecular mass muchhigher, so that the ab).......................................... forcesbetween molecules are stronger. The plastic isac)............................... and more ad)............................... so it isused for ae)....................................................................................

�• Polystyrene is made from the monomer af)..........................for which the correct systematic name is ag)............................................................. The �“side group�” on this molecule isthe ring-shaped ah)................................... group. Thisincreases the molecular mass so that the ai).............................forces hold the polymer molecules even more strongly sothe plastic is aj)....................................... and ..............................

Polymers can also form by a ak)........................................reaction. This occurs when 2 monomer molecules jointogether by elimination of a al)..................................................Examples of condensation polymers are nylon,am)........................................ and .................................... Allbiological polymers, such as an)..................................... and............................................... are condensation polymers.

One important biological polymer is ao).................................which is a polymer of ap)................................. and is foundin large amounts in all plants, where it forms the cellaq)................................ which strengthens and protects allplant tissues. We already use cellulose for fabrics such asar)................................... and ................................. and processit to make as)....................................... When the petroleumsupplies run out, cellulose has great potential to supply ourneeds.

Its monomer at)............................... can easily be turned intothe alcohol au).................................... which can be used as afuel, or chemically converted to av).........................................to feed the plastics industry. Unfortunately, we have not yetdeveloped a simple, efficient and economical way toconvert cellulose to aw)................................... to begin theprocess.

Research is also progressing in the use of engineered�“Biopolymers�” such as ax)...................... (abbreviation). Thispolymer has properties similar to some petrochemicalplastics, but is made naturally by microbes such as thebacterium ay)........................ ................................ (scientificname). The Monsanto company has used az).......................................................... techniques to transfer the genes forPHB into ba)................................. plants. After normalgrowth and harvesting, PHB can be extracted from the�“waste�” leaves and stems of the crop.

Although this is very promising, it is unlikely to be used ona large scale while cheaper petrochemicals are still available.

9





WHEN COMPLETED, WORKSHEETSBECOME SECTION SUMMARIES

The Alkanols (Alcohols)You should recall that the Alkanes and Alkenes are 2�“Homologous Series�” of compounds. In each series, thecompounds follow a pattern of having the same basicstructure, and are able to be described by a generalmolecular formula.

Series General Structure Formula

Alkanes all single C-C bonds CnH2n+2

Alkenes one C=C double bond CnH2n

Now you are introduced to another importantHomologous Series... the Alkanols, also known as�“Alcohols�”.

The alkanols contain all C-C single bonds, but on one ofthe carbon atoms there is an -OH group... an oxygen atomand hydrogen atom.

Methanol CH3OH(Formula could be written CH4O,but it is usual to emphasize the -OH group)

Ethanol C2H5OH

This is by far, the most importantmember of the series.

Condensed StructuralFormula

CH3CH2OH

Propanol C3H7OH

CH3CH2CH2OH

and then...Butanol C4H9OH CH3(CH2)2CH2OHPentanol C5H11OH CH3(CH2)3CH2OHHexanol C6H13OH CH3(CH2)4CH2OHHeptanol C7H15OH CH3(CH2)5CH2OHOctanol C8H17OH CH3(CH2)6CH2OH

Properties of the AlkanolsWhat a difference that oxygen atom makes!

The polar covalent bond in the -OH group creates a chargedipole, and strong hydrogen bonding exists between themolecules.

This results in:�• mp�’s and b.p�’s being much higher than the correspondingalkanes. The first 8 alkanols are all liquids at roomtemperature.

�• smaller alkanols are soluble and fully miscible in water,because they can form hydrogen bonds with watermolecules. The larger ones become less soluble as the non-polar hydrocarbon chain grows longer.

�• the alkanols (especially ethanol) are excellent solvents,able to dissolve many water-soluble (polar) solutes, but alsoable to dissolve many non-polar substances which do notdissolve well in water. This is why ethanol is widely used inindustry to dissolve reagents, pharmaceuticals and foodchemicals. Around the home �“methylated spirit�” is used asa cleaning agent... it dissolves things well.

(Methylated Spirit, or �“metho�” is about 95% ethanol withwater and small amounts of additives to make it distastefulto discourage anyone from drinking it)

�• alkanols are inflammable, and can be used as fuels,although their energy content is not as high as thecorresponding alkanes.

Ethanol is, of course, the alcohol in beer, wine and spirits.These are made by the process of fermentation carriedout by living microbes, especially yeast, which is a single-celled fungus organism.

You should be aware that, despite our society�’s acceptanceof the consumption of alcohol as a social drug, all thealcohols are toxic. Our bodies can tolerate ethanol in smalldoses, but others such as methanol or propanol, are quitedeadly.

10


2. ALTERNATIVE FUELS - ETHANOL & THE ALKANOLS




To name any ALKANOLadd �“-ANOL�” to the appropriate prefix.

General Formula CnH2n+1OH

O-HH

HH

H

C

H O-HH

H

H

H

H

C C

H H O-HH

HHH

H

H

C C C

""+""-

Polar Covalent BondNon-PPolar CovalentBonds creates

electricchargedipole

Ethanol




11

Ethylene to EthanolEthylene can readily be converted to ethanol by anAddition Reaction across the double bond. You may haveused molecular model kits to help visualize this reaction.

The reaction is facilitated by dilute sulfuric acid, which actsas a catalyst.

CH2=CH2 + H2O CH3-CH2-OH

Ethanol to EthyleneThe reverse reaction is also possible:

CH3-CH2-OH CH2=CH2 + H2O

Once again a catalyst is need to make the reaction run at apractical rate for an industrial process. The same catalyst,sulfuric acid, is used but in concentrated (not dilute) form.

Since water is produced as a product, it is reasonable todescribe the reaction as a �“Condensation�”, but it is alsoknown as a �“Dehydration�”, meaning to �“take water from�”.

The significance of this reaction is that ethanol can bemade from plant materials, by processes that are renewableand sustainable. Making ethylene from ethanol would resultin a major chemical resource being available without theuse of petrochemicals.

Model of Ethanol Dehydration

Fermentation of Sugar to EthanolThe fermentation process is the oldest known chemicalprocess used by humans. We don�’t really know when it wasdiscovered by ancient peoples, but the brewing of beer andwine was practiced by all the early civilizations of theMiddle East, Europe and Asia.

The overall chemical reaction is very simple:

Glucose Ethanol + Carbon dioxide

C6H12O6(aq) 2 C2H5OH(aq) + 2 CO2(g)

It looks simple enough, but the actual chemistry is verycomplicated, involving many separate steps, each catalysedby a different enzyme produced by the living yeast cells.

However, you don�’t need to know all those details, and justlike any maker of home-brew beer soon finds out, it reallyis simple as long as you provide certain conditions. Forfermentation to work there must be:

�• a suitable carbohydrate source. This can be sugar fromfruit, starch from wheat, corn, potatoes, etc. (Note that theyeast is able to digest starch and other carbohydrates toglucose, so it is not necessary to actually start with glucose.)�• live yeast.�• a temperature kept fairly constant around 22-25oC.�• anaerobic conditions (i.e. no oxygen available). If oxygenis available, the yeast will produce only CO2 and H2O, butno alcohol.

dilute H2SO4 catalyst

+

conc. H2SO4 catalyst

+Ethanol

WaterEthylene

yeast

Practical Work FermentationYou may have carried out an experiment with fermentationwhich is essentially a little �“home-brew�” exercise.

The photo shows a typical laboratory set-up.

Sealed flaskcontainssugar &yeast.

Temp. keptat about25ooC

You may have weighed the flask before, and after, severaldays of fermentation. It will have lost mass due to the lossof gas.

You would also observe bubbling in the flask over severaldays, and the limewater would rapidly go �“milky�” provingthat the gas produced is CO2.

When the bubbling subsides, the contents of the flask mayhave the yeasty, alcohol smell of beer.

You may have even distilled your brew to collect ethanol, asdescribed at left.

Any gas producedbubbles through abeaker of limewater

Fractional Distillation of Your �“Home-Brew�”

Heat gently and monitor the vapour temp.Collect the fraction produced at about 80oC.

To test your distillate: pour into a watch glassand ignite carefully in a darkened room orfume-cupboard. If it burns with a blue flame,your distillate is 80-90% ethanol.



12

Getting Pure EthanolEven under ideal conditions the fermentation of sugar toethanol by yeast can only produce a �“brew�” with about15% ethanol. At about this level, the yeast is killed by thealcohol, and no further fermentation takes place.

To get close to pure ethanol, the fermented liquor must bedistilled. In the making of brandy, whiskey, rum, etc, the�“spirit�” is usually around 40% ethanol.

Fractional distillation will yield a distillate which is about95% ethanol, which is quite suitable as a fuel.

The Industrial Process TodayDue to the cheap availability of petrochemicals, most ofthe ethanol used as an industrial solvent or for cleaning (i.e. non-drinking purposes) is made from ethene by theaddition reaction with water, and NOT from thefermentation of sugar.

The only industrial-scale use of fermentation to makehigh-purity ethanol is in the sugar industry. A major wasteproduct from sugar refining is �“molasses�” which contains alarge amount of sugar. Rather than waste it, molasses isused as the sugar source for yeast fermentation, and thefermented liquor is distilled for the ethanol.

In Australia, the sugar industry is based in Queensland, andthis is where the sugar-to-ethanol production takes place.Apart from producing the famous �“Bundy�” rum, theethanol produced is used for:

�• manufacture of vinegar.�• �“extending�” petrol by adding 10% ethanol. (more later)�• industrial and pharmaceutical solvent.�• domestic cleaner, in the form of �“metho�”.

Combustion of the AlkanolsEthanol has been mentioned as a possible fuel, so what isthe chemistry of the combustion?

Basically it is the same as combustion of the alkanes:

alkanol + oxygen carbon dioxide + water

Example: Combustion of Ethanol

C2H5OH(g) + 3O2(g) 2CO2(g) + 3H2O(g)

The only tricky part is balancing... be careful balancing theoxygen atoms, noting that there is already 1 oxygen atomon the left side in the alkanol molecule.

Heat of Combustion of a FuelHow much energy is actually released when a fuel burns?

All combustion reactions are exothermic, so the energyprofile is

Although technically the value for #H is a negative quantity,for �“Heat of Combustion�” the value is usually written as apositive quantity because the formal definition is:

The Molar Heat of Combustion is the heat given outwhen 1 mole of a fuel is burned completely, with allreactants and products in their �“standard states�” at SLC.

Notes:1. Since the definition is the �“heat given out�”, it follows that thevalue is expressed as a positive quantity. You must remember thatcombustion is exothermic, and technically it has a negative value,for example when using an equation such as #H = -mC#T.2. You learned previously that fuels generally burn only after beingvaporized, and that the water forms in the gas state, as shown inthe equation above. However, the definition demands that allsubstances are in their �“standard states�” at SLC, so both ethanoland water must be in the liquid state.

So, the Molar Heat of Combustion (##Hc) of ethanol would bethe (positive) quantity of heat released when 1 mole of ethanol(=46.1g) burns as follows: (note the states)

C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l)



Try the worksheet at the end of this section

Reactants

Ener

gy C

onte

nt

Products

##H negative

EaEaa = Activation

Energy

Read the labels



13

Prac Work Measuring ##Hc of AlkanolsYou may have carried out experiments to measure andcalculate values for the Heat of Combustion of severalalkanol fuels. A typical school experimental set-up is shown:

Thermometer measures temp.change in water.

Metal can holds a measuredquantity of water. It acts as acalorimeter, absorbing heatreleased by the fuel.

�“Spirit burner�” burns analkanol fuel using a wick.Burner is weighed before andafter to measure the mass offuel used.

Typical results using Ethanol:

Mass of ethanol burnt = 0.80g

Mass of water in metal can = 100g

Starting temperature of water = 16oCFinal temperature of water = 42oC

#T = 26oC

Analysis of Results:Heat absorbed by water in the calorimeter:

##H = -mC##T (C = Specific Heat Capacity of= - 100 x 4.18 x 26 water = 4.18 J/oC/g)= - 10,868 J$ 11 kJ of heat released.

This is the heat released for 0.80g of ethanol burnt.

% Heat of Combustion per gram = 11/0.80 = 13.75 kJ/g

MM(ethanol) = 46.1g

% Molar Heat of Combustion = 13.75 x 46.1 $ 630 kJmol-1.

Discussion:The �“text book value�” of #Hc (ethanol) = 1367 kJmol-1.Typically, in a school experiment, values of only about half, orless, are obtained. Why?

The analysis of results assumes that all the heat released by theburning fuel is absorbed by the water in the �“calorimeter�” can.However, this calorimeter is very primitive and inefficient. A lotof (most of?) the heat of the fuel can escape into thesurroundings, and therefore does not get measured.

The set-up can be improved by using a larger can, wind baffles,insulation, etc., but will always give results well below �“text�”values.

Comparing ##Hc of FuelsThe syllabus requires that you measure and compare theHeat of Combustion for at least 3 different alkanols, on aper gram, and per mole basis.

Hopefully you�’ve done exactly that. To help you understandthe figures, here is a summary of typical results. Forcomparison purposes, values for an alkane fuel (octane is atypical component of petrol) are included.

Heat of Combustion ValuesFuel School Experiment �“Text�”

kJ/gram kJmol-1 kJ/gram kJmol-1

Methanol 10 350 22.7 726

Ethanol 11 630 29.7 1367

Propanol 12 720 33.6 2021

Butanol 14 1040 36.1 2676

Octane - - 47.9 5470

Although the values that are typically obtained in a simpleschool experiment are well below the accepted �“text�”values, the trends are the same: the Heat of combustionof the alkanols increases steadily (on both per gram and permole basis) with increasing molecule size.

It is notable also, that ethanol�’s #Hc is much lower than thetypical value for the compounds found in petrol. Thismeans that ethanol, a candidate to replace petroleum fuels,is a much lower-energy fuel.

Ethanol as a Renewable FuelThe use of ethanol as a fuel to eventually replace petrol, asthe petroleum supplies run out, has been proposedbecause:

�• the technology to make ethanol from the fermentation ofsugar (followed by distillation) is a well known and provenprocess... we know it can be done.

�• sugar for ethanol production can be harvested fromplants, so it is a renewable, and sustainable energy source.

�• when ethanol from plants is burnt, the carbon dioxidereleased is exactly the same amount that was absorbed bythe plants during photosynthesis to make the sugar.Therefore, the use of plant-derived ethanol does notcontribute to the �“Greenhouse Effect�”.

There is no doubt that ethanol can be considered as arenewable fuel.

However, that�’s not the whole story...





14

Using Ethanol as an Alternative to PetrolEthanol can be added to petrol in mixtures up to about 10-20% and burnt in car engines without any modificationsneeded, and with only a slight loss of engine performance.

This use of ethanol as an �“extender�”, to conserve petroland help reduce Greenhouse emissions has been aroundfor years on a small scale. Following the fuel price crisis of2005, the Australian Government has proposed making ithappen on a very large scale.

As long as the ethanol is being made from the wastes ofthe sugar industry, and used only at about the 10-20% levelwith petrol, this strategy seems both economical andscientifically sound.

To run vehicles on pure ethanol fuel however, requires atotal new engine design to allow for the fact that ethanoltends to be corrosive, has a different energy content,ignition temperature and burn characteristics.

The cost of setting up factories to make a totally newengine design is such that it is very unlikely that ethanol willbe used as any more than a 20% fuel-extender anytimesoon.

Advantages & Disadvantages of Ethanol Fuel

Some of the Advantages have already been discussed:

�• Ethanol is a renewable fuel, when made from sugar.

�• The technology is already known and proven.

�• It is �“Greenhouse-friendly�”.

�• It can be mixed with petrol up to about 20% and usedwithout any modifications to existing engines.

This, however, is only part of the story...

Disadvantages and Difficulties�• To totally replace petrol with ethanol, the use of sugarindustry wastes would be nowhere near enough. Hugetracts of land would have to be dedicated to growing sugarcane (or other crops) to supply the ethanol industry. Theattempt by Brazil to do exactly this in the 1980�’s was aneconomic failure, and disrupted a lot of their foodproduction farming to make way for �“ethanol farming�”.

�• The current technology for ethanol production requiresmassive amounts of energy for the distillation process.Currently, fossil fuels are used for the heating, and so theprocess is not as renewable nor �“Greenhouse-friendly�” asfirst thought.

�• As mentioned at left, entirely new engines are needed torun on pure ethanol. The cost of the change-over, to bothmanufacturers and car-owners is too high to be feasible.

AssessmentWeighing up advantages and disadvantages, the followingconclusions seem realistic:

�• The use of about 10-20% ethanol (derived from sugarindustry wastes) to extend petrol seems likely to continueand even become more widespread.

�• The use of pure plant-derived ethanol fuel seems veryunlikely until one or both of these technologies develops;

- efficient production of glucose from cellulose,derived from crop wastes, so that no crops haveto be grown just for ethanol production.

- renewable energy sources (e.g. solar power) tooperate the distillation process for ethanol.



Sugar Cane Harvesting

Photo ©Robert Lincolne 2006Used with permission

Worksheet 2

Part A Fill in the Blank Spaces

The Alkanols are an a)....................................... series ofcarbon compounds with general formula b)..........................They are also known as the �“c)................................�” Eachalkanol has an d)................... group attached to one of thecarbon atoms. This group contains a e)................................covalent bond which creates an electric f)............................on the molecule. This causes quite strong g)..........................bonds between the molecules, which result in the followingproperties:

�• m.p.�’s & b.p.�’s are much h)..................................... than thecorresponding alkanes.�• alkanols are generally i)............................... in water.�• they are excellent j).............................., because they candissolve both k)............................... and ...................................(opposites) solutes.�• they are inflammable, and can be used as l).......................,although their m).................................................. is lower thanthe alkanes.

Ethylene can be converted to ethanol by an n)........................reaction, adding o).............................. across the doublebond. Dilute p)................................................... acts as acatalyst for this reaction. The reverse reaction, convertingq)...................................... to ........................................ is alsopossible if r).................................. H2SO4 is the catalyst. Thisreaction could be considered as a �“condensation�”, but isusually referred to as �“s)..........................................�”

Biologically, ethanol can be made from t)...............................by the process of u)............................................ The catalystsare the v)..................................... in living w)..............................cells. The requirements for the reaction are:�• a suitable source of x).................................... from fruits orgrains.�• live y)............................�• at temperature maintained around z)..................oC�• aa)............................................ conditions (no oxygen).

Fermentation can produce a mixture containing amaximum ab)..................% ethanol. This can be purified byac).................................................................... to obtain aboutad)...................% purity. Industrial scale fermentation (apartfrom beer & wine production) uses wastes from theae)........................................ industry, and then fractionalaf)..................................... to obtain near-pure ethanol formanufacturing ag).................................... (food use) or forsolvent and cleaning purposes.

When alkanols burn, the products of complete combustionare ah)............................................. and ..................................The �“Molar Heat of Combustion�” is defined as ai)......................................................................................................................with all reactant & products in their aj)...................................

Although the reaction is always ak)..............-thermic andshould have a al)............................. value for #H, the value isstated as a am).................................... quantity because of thedefinition.

Generally, the values for #Hc for the alkanolsan)................................ with increasing molecular size, butare much lower than the values for an ao)...............................

The advantages of using ethanol as a fuel are�• it is a ap).......................................... resource�• the aq)................................................ is known & proven�• it is �“ar)......................................-friendly�”�• it can be mixed with petrol to about as)..............% withoutany modifications to existing car engines.

Disadvantages include:�• to totally replace petrol, vast areas of land would have tobe at)..............................................................................................�• large amounts of energy are needed for the au)........................................................ process, and we cannot yet do this ina renewable and eco-friendly way.�• vehicle av).............................. would have to be totally re-designed and replaced to run on pure ethanol.

Part B Practice Problems

1. Combustion Equations for AlkanolsWrite a balance equation for the complete combustion ofa) methanol b) propanolc) hexanol d) octanol

2. Heat of Combustion Problemsa) In an experiment, 1.4g of butanol was burnt and the heatcollected by a metal can containing 200g of water. Thewater temperature rose by 23oC.

i) Write a balanced equation for the combustion,showing all chemicals in their standard states.

ii) Calculate the value of #Hc per gram & per mole.

b) In a similar experiment using pentanol, 0.50g of fuel wasburnt, which raised the temperature of 150g of water from18 to 30oC.

i) Write a balanced equation for the combustionshowing all chemicals in their standard states.

ii) Calculate the value of #Hc per gram & per mole

c) The accepted value for #Hc(ethanol) = 1367 kJmol-1.If 2.80g of ethanol was burnt in a �“perfect�” calorimetercontaining 500g of water, by how much would thetemperature of the water rise?

d) The accepted value for #Hc(pentanol) = 3330 kJmol-1.If 0.50g of pentanol was burnt in a �“perfect�” calorimetercontaining 150g of water, by how much would thetemperature of the water rise?Compare your answer to the data in Q(b) and comment.

15





Displacement of Metals From SolutionAnd now for something completely different, we go back tosome Chemistry you learned in Preliminary topic 2�“Metals�”. Remember the Activity Series of the Metals?

One of the best �“hands-on�” ways to see the Activity Seriesin action is to place a piece of metal into a solutioncontaining the ions of a less-active metal. This experimentis not actually specified by the syllabus, but hopefully youhave seen what happens.

Example:Drop a piece of zinc into copper(II)sulfate solution.

A reaction occurs which slowly�“eats away�” the zinc, and a soliddeposit forms at the bottom. Later,the deposit is seen to be orange-coloured... it is copper metal.

The zinc has dissolved, anddisplaced the copper ions fromsolution.

The reaction is

copper(II) + zinc zinc + coppersulfate sulfate

CuSO4(aq) + Zn(s) ZnSO4(aq) + Cu(s)

This is a �“Metal Displacement�”. It will occur whenever ametal is placed into a solution containing ions of a less-active metal. The reverse will not react.

Transfer of ElectronsThe equation above can be re-written in ionic form:

Cu2+(aq)+SO4

2-(aq)+Zn(s) Zn2+

(aq)+ SO42-

(aq)+Cu(s)

Look carefully and you will see that the sulfate ions (SO4

2-) have not changed at all... they are �“spectators�” andcan be left out, to form the �“net ionic equation�”:

Cu2+(aq) + Zn(s) Zn2+

(aq) + Cu(s)

Now you can see what really happened; copper ions turnedinto copper atoms, and zinc atoms turned into zinc ions.This can only happen if:

each copper ion gains 2 electrons

Cu2+(aq) + 2e- Cu(s)

and each zinc atom loses 2 electrons

Zn(s) Zn2+(aq)+ 2e-

This is one of the most common and importantgeneral types of chemical reaction; when electrons aretransferred from one chemical species to another.

Note that neither part can occur alone. To lose electrons,there must be another species to accept them, and to gainelectrons, there must be another species to give them.

16


3. REDOX CHEMISTRY & BATTERIES




K

Na

Li

Ba

Ca

Mg

Al

Zn

Fe

Sn

Pb

Cu

Ag

Au

MostActive

LeastActive

React readily with

�• oxygen�• water�• acid

Dec

reas

ing

reac

tivity

No reaction, or very slow

Electrons transferred

Loss of Electrons = �“OXIDATION�”

Gain of Electrons = �“REDUCTION�”

Reactions where this occurs are called�“OXIDATION-REDUCTION�”

or simply

�“REDOX�”




17

REDOX and the Activity SeriesNow the Activity Series of the metals can be seen in a newway.

�• Metals higher up the Activity Series have a greatertendency to be oxidized (= lose electrons) and so theiratoms readily form ions by reacting with acids, oxygen,water, or the ions of less active metals.

�• Metals lower down the Activity Series have a greatertendency to be reduced (= gain electrons). Their atoms areless likely to react with acids or oxygen, and their ions aremore likely to be displaced from solution by more activemetals.

You should recall also, that less active metals are easier toextract from their ores, (or may even be found uncombinedin nature) while more active metals require more and moreenergy to extract from their ores. Extracting any metalfrom its ore involves reducing the metal�’s ions, so this idealinks to that above.

Galvanic CellsJust because Oxidation & Reduction must always occurtogether doesn�’t mean that they must occur in the samecontainer.

It was discovered about 200 years ago that the 2 processescan be separated to 2 different locations, so long as there isa conducting wire to allow the flow of electrons from thesite of oxidation to the site of reduction.

This forms a �“Galvanic Cell�” which is the basis of all ourelectric cells and batteries.

�“Galvanic�” isnamed for one ofthe pioneeringscientists, theItalian LuigiGalvani who lived200 years ago. Atthat time, electrontransfer and REDOX chemistry was NOT understood.

Prac Work: Galvanic CellsYou may have done several experiments to investigate theconstruction of simple Galvanic Cells, and to measure thevoltage (�“potential difference�”) produced by differentcombinations of metals.

A typical experimental set-up is shown.

Zinc electrode Copper electrodein solution of in solution ofzinc ions copper ions

TThheeyy mmuusstt bbee ccoonnnneecctteedd bbyy aa �“�“ssaalltt bbrriiddggee�”�” ffoorr iioonn ttrraannssffeerr

Each beaker is a �“half-ccell�”, containing ametal electrode dipping into a solutionof ions of the same metal.

What You May Have Discovered

Conditions under which a Galvanic Cell works�• Half-cells must be connected by a wire to allow electronflow from one to the other.�• Half-cells must be connected by a �“salt-bridge�”

(explanation next page)�• Electrodes must be 2 different metals.�• Electrodes must dip into an

�“electrolyte�” solution containing ions.

Which Electrode is Which?You will quickly find that if you connectthe voltmeter the wrong way around,that the needle deflects backwards.

To make it read correctly, the moreactive metal is always connected to thenegative connection.

This is because the more active metalalways oxidizes (loses electrons).Therefore, electrons flow from the moreactive metal.

The Size of the Potential DifferenceIf you test various combinations of metals (but always usethe same concentration of solutions) you will find that...

...the further apart the metals are inthe Activity Series, the higher the cellvoltage (potential difference).

Connecting wiresallow electrons toflow from one half-cell to the other

Voltmeter




18

A Typical Galvanic Cell

VVoltmeter

Salt Bridge

eelleeccttrr

oonn ffll

oowwiinn

wwiirreeeelleeccttrroonn ffllooww

ANODEHalf-ccell where

OXIDATION occurs

If both electrodes are metals,this will be the

more active metal

CATHODEHalf-ccell where

REDUCTION occurs

If both electrodes are metals,this will be the

less active metal

Typical Anode Reaction

Metal Metal + electronsatoms ions

example

Zn((ss)) Zn22++((aaqq)) + 2e-

The zinc electrode would dissolve,as zinc ions go into solution

Typical Cathode Reaction

Metal + electrons Metalions atoms

example

Cu22++((aaqq)) + 2e- Cu((ss))

Solid copper deposits onto the electrode

+ve

+ve

-vve

-vve

EElleeccttrroollyytteessoolluuttiioonne.g.ZnCl22 solution

An �“Electrolyte�” is a substance which willconduct electricity whenmolten, or in solution.

Generally, it refers toionic solutions

The Salt Bridge can be just afilter paper soaked in

electrolyte, or a tube ofelectrolyte jelly, or even justthe electrolyte solution itself.

It must allow diffusion ofions from one half-ccell to the

other

Electrons always flow from ANODEto CATHODE in the external circuit

Spectator IonsBe aware that there must beother ions in the solutions as

well. For example, thesolutions shown contain Cl-and SO44

22- ions as well as themetal ions. They take nopart, except to migratethrough the Salt Bridge.

An �“Electrode�” is a conductor placed in each

half-ccell to pick up orrelease electrons.

Sometimes the electrode isinvolved in the reaction; inother cases it can be �“inert�”.

Zn Cu

EElleeccttrroollyyttee ssoolluuttiioonne.g.CuSO44solution

Ions migrate throughthe Salt Bridge to keep

the total charge ineach half-ccell neutral

Definitions&

Things To Know...

Each cell can be described bya �“short-hhand�”. The cell above

would be described by

Zn|Zn22++ || Cu22++|Cu

aannooddee ssaalltt ccaatthhooddeessppeecciieess bbrriiddggee ssppeecciieess




19

Standard Electrode PotentialsThe actual voltage reading you get when you set up anelectrochemical cell depends on many factors:

�• the metals used at the electrodes (in particular, how far apart the 2 metals are in the Activity Series)

�• the concentration of electrolyte solutions�• the temperature�• the gas pressure, if any gases are involved

Therefore, to make comparisons and predictions, it isnecessary to specify a set of standard conditions formeasuring the voltage of any cell.

The standard conditions are (predictably) �• all solutions are 1.0 molL-1

�• temperature and gas pressure at SLC (25oC & 1 atmos)

Under these conditions, each half-cell has a �“StandardElectrode Potential�” when measured against a �“ReferenceHalf-Cell�”. The reference used is the reaction

2H+(aq) + 2e- H2(g) Eo = 0.0 V

This half-cell has been assigned a Standard ElectrodePotential (Eo) of zero volts, and all other half-cells aremeasured from this.

You may have been given a �“Chemistry Data Sheet�”containing a list of standard electrode potentials. Here is ashorter version for quick reference, which will be usedthroughout these notes and exercises.

Some Standard Potentials Eo (V)

Ca2+ + 2e- Ca(s) -2.87

Mg2+ + 2e- Mg(s) -2.36

Zn2+ + 2e- Zn(s) -0.76

Fe2+ + 2e- Fe(s) -0.44

2H+ + 2e- H2(g) 0.00

Cu2+ + 2e- Cu(s) +0.34

I2(aq) + 2e- 2I-(aq) +0.62

Fe3+ + e- Fe2+(s) +0.77

O2(g)+ 4H+(aq) + 4e- 2H2O(l) +1.23

Cl2(aq) + 2e- 2Cl-(aq) +1.36

Notice that each half-equation is written as a reduction. Ifyou need to write it backwards as an oxidation, then simplyreverse the sign of the Eo value.

Using Electrochemical DataConsider the cell described previously, which containedzinc and copper electrodes in solutions of matching ions.

The Half-Cell reactions, with Eo values are:Eo

Zn(s) Zn2+(aq) + 2e- +0.76 V

Cu2+(aq) + 2e- Cu(s) +0.34 V

__________Total Cell Voltage = +1.10 V

This means that, under standard conditions, this cell willproduce a voltage (technically, an �“Electromotive Force�”(EMF), or �“Potential Difference�”) of 1.10 volts.

Notes:1. The zinc reaction was written as an oxidation, the reverseof the half-cell equation given in the table at left. Since theequation was reversed, the sign of the Eo value wasreversed also.

2. The total cell voltage is simply the sum of the half-cellEo values.

3. The overall equation for the reaction can be found bysimply adding together the 2 half-equations, being sure thatthe same number of electrons are on each side andtherefore, �“cancel-out�” as follows:

Zn(s) + Cu2+(aq)+ 2e- Cu(s) + Zn2+

(aq)+ 2e-

Any 2 half-equations can be combined this way, butsometimes it may be necessary to multiply one or both bya factor so that the electrons will cancel.

Example:Cl2(aq) + 2e- 2Cl-(aq)

combined withFe2+ Fe3+

(s) + e-

You need to multiply everything in the 2nd equation x2before combining them

Cl2(aq)+ 2e- + 2Fe2+ 2Fe3+(s)+ 2e- + 2Cl-(aq)

However, when you do this, the Eo values DO NOT CHANGE

V

Zn

e-

Zn22++ Cu22++

Cu

Short-HHand

Zn|Zn22++ || Cu22++|Cu




20

Using Electrochemical Data (continued)So, how do you know which half-equation to reverse andwrite as an oxidation?

Simple! In all �“Galvanic Cells�” the sum of the Eo values must be apositive voltage. THE HALF-EQUATION HIGHERUP THE �“STANDARD POTENTIALS�” TABLEMUST ALWAYS BE REVERSED AND WRITTENAS AN OXIDATION.

Study this example:

Note: this electrode isnot involved in thechemistry of the cell.It simply serves as �“pick-up�” for electrons.

From the table, the half-cell reactions involved must be:Eo

Cu2+ + 2e- Cu(s) +0.34and

I2(aq) + 2e- 2I-(aq) +0.62

The copper equation is higher up the Standard Potentialstable, so it must run in reverse as an oxidation. Don�’t forgetto reverse the sign of the Eo value too.

Cu(s) Cu2+ + 2e- -0.34

Now combine the half-equations to form the overallequation, and add the Eo�’s to get the total cell EMF.

I2(aq)+ 2e-+ Cu(s) Cu2++ 2e-+ 2I-(aq) +0.62

-0.34Total Cell EMF = +0.28 V

In the diagram above, the Copper half-cell is the ANODE(oxidation) and the Iodine half-cell is the CATHODE(reduction). Electrons would flow from the copperelectrode towards the graphite (carbon) electrode.

The �“Shorthand�” description for this cell is:

Cu|Cu2+ || I2|I- (C)

Notes1. There would also be �“spectator ions�” in each half-cell.They have been totally ignored above.

2. Inert electrodes are used whenever a metal is notinvolved in one of the half-reactions. Compressed graphite(carbon) is commonly used. Platinum (Pt) is the best, butvery expensive.

V

Cu22++

CuInert graphiteelectrode

Inert electrodein brackets

Oxidation States & NumbersWe use a simple number system to describe the �“oxidationstate�” of any chemical species.

�• neutral elements, in their normal state,have oxidation number = zero

�• simple ions, oxidation number = charge on ion

Examples: Species Oxidation numberiron atom Fe(s) 0

iron(II) ion Fe2+(aq) +2

iron(III) ion Fe3+(aq) +3

chloride ion Cl-(aq) -1

chlorine molecule Cl2(aq) or (g) 0

If, during a REDOX reaction the oxidation number of aspecies increases, then it has been OXIDIZED.

If, during a REDOX reaction the oxidation number of aspecies decreases, then it has been REDUCED.

Examples of Half-Equations with Oxidation Numbers

Fe(s) Fe2+(aq)

ox�’d no. 0 +2Ox�’d number has increased, % Oxidation has occurred.

2Cl-(aq) Cl2(g)ox�’d no. -1 0Ox�’d number has increased, % Oxidation has occurred.

Fe3+(aq) Fe2+

(aq)ox�’d no. +3 +2Ox�’d number has decreased, % Reduction has occurred.

2H+(aq) H2(g)

ox�’d no. +1 0Ox�’d number has decreased, % Reduction has occurred.

Wherever an oxidation has occurred, electrons have beenlost. If you add electron(s) to the RIGHT side of the half-equation, the charges will balance.

e.g. from above, Fe(s) Fe2+(aq) + 2e-

For reductions, add electron(s) to the LEFT side.

e.g. from above, 2H+(aq)+ 2e- H2(g)

Try the WORKSHEET at the end of section

I22((aaqq))

andI-((aaqq))



21

More on Galvanic Cells (Optional)Galvanic Cells are those which run spontaneously, andproduce energy, in the form of electricity.

This means that the reactions involved are Exothermic.

The size of #H in the energy profile is related to the cellEMF (voltage) produced by a Galvanic Cell. Confusingly,for exothermic reactions #H is defined to be negative,while the cell voltage must be positive. This is entirely dueto the definitions involved, and is not really a contradiction.

What if the Cell Voltage is Negative?Lets take the same cell that has previously been used as theexample, and write both half-equations in reverse:

Eo

Zn2+ + 2e- Zn(s) -0.76 V

Cu(s) Cu2+ + 2e- -0.34 VCell EMF = -1.10 V

What does this mean?

The cell is NOT �“Galvanic�”. It will NOT runspontaneously. Instead of producing electricity, you wouldhave to put electricity INTO the cell (minimum 1.10 Volts)to make these reactions run.

The overall reaction is Endothermic.

To make this cell, you could use exactly the same half-cells,but instead of connecting a voltmeter in the circuit, youwould need to place an electrical source, such as a batteryor �“power pack�” to provide energy.

Notice that all the half-equations in the �“StandardPotentials�” table are shown with double arrows.This is to indicate that each reaction is reversible, and canrun in either direction, depending on the energy situation.



Reactants

Ener

gy C

onte

nt

Products

##H

Ea Eaa = Activation Energy

For ions in solutionin a galvanic cell,the Ea is very low

Energy is releasedby the reaction

Reactants

Ener

gy C

onte

nt

Products

##Hpositive

Ea

Eaa = Activation Energy

Energymust be putIN, to makethis reactiongo.

Electricalsource

Zn Cu

Cu22++Zn22++

Electron flow

The material on this page is NOT requiredlearning according to the Syllabus.

It has been included in the interests of better understanding.

Endothermic Cellslike this are called�“Electrolytic�”

All Dry Cells & Batteries

are Galvanic Cells......spontaneous, Exothermic,

with positive cell voltage

�“Battery�”

�“Cell�”

(The difference is explainedsoon)



22

Cells & BatteriesFirstly, what�’s the difference?

A cell is an electrochemical unit with just one anode andone cathode. A �“battery�” is 2 or more cells linked togetherto provide more power. When you place 2 or more cellsinto a flashlight you are making a battery. A car battery ismade of six cells connected together. Each cell provides 2volts, and the entire battery gives 12 volts.

In everyday usage, this is called a �“battery�”,but in fact it is a cell.

This �“battery�” really is a battery.Inside are 4 connected cells,each 1.5 volts.

The entire device gives 6 volts.

The �“Ordinary�” Dry Cell (Leclanche Cell)The original cells and batteries were all �“wet cells�”, in thatthey contained liquid solutions which had to be keptupright and tended to be large, messy and not easilytransported. A vital use was the Morse Code Telegraph.

The first �“dry cell�” was invented by Leclanche in 1866, anddeveloped to commercial standard by Gassner in 1881. Theelectrolyte solution is a thick �“paste�”, and the entire cell issealed against spillage, and easily transported.

Structure of a Dry Cell

Chemistry of the Leclanche CellOxidation at the Anode:

Zn(s) Zn2+(aq) + 2e-

Reduction at the Cathode:NH4

+ + MnO2 + H2O + e- Mn(OH)3 + NH3

To get the overall cell reaction, you need to firstly multiplythe cathode equation x2, so the electrons will cancel.

2NH4++ 2MnO2 + 2H2O +2 e- + Zn

2Mn(OH)3 + 2NH3 + Zn2+ + 2e-

Cost, Practicality and Impact on SocietyThe standard dry cell is very cheap to produce, and can bemade in a variety of sizes so it is very practical as a powersource for flashlights, remote controls, portable radios,many toys, calculators, etc.

For more power, multi-cell batteries (photo at left) can bemade to power larger flashlights or other devices.

In fact, the dry cell encouraged the development of allthese devices. Small portable electrical devices would neverhave been invented if cells and batteries had not beenavailable to power them.

Environmental Impactof this technology is minimal, since the chemicals involveddo not cause any significant problems when disposed ofinto landfill rubbish dumps.

The Silver Oxide �“Button Cell�”There is a limit to how small you can make a standard drycell and still get a practical amount of electricity from it.

The development of really small electrical devices such ashearing aids, digital watches and remote-locking devices forcars, was made possible by the invention of the �“Button Cell�”. Structure

ChemistryOxidation at the Anode

Zn(s) Zn2+(aq) + 2e-

Reduction at the Cathode:Ag2O + H2O + 2e- 2Ag + 2OH-

So, overall reaction is:

Ag2O+ H2O + 2e-+ Zn 2Ag + 2OH-+ Zn2++2e-

Button Cells are relatively expensive, but last a long timein miniature, low-energy devices. Their tiny size and goodperformance are worth the expense.

Environmental Impact is low because these cellscontain so little material,and the relatively inertstainless steel and silvermetal inside them is not asignificant environmentalhazard.



Positive Terminal

Insulating seal

Graphite rod (CATHODE)Electrolyte paste containing

NH4Cl and MnO2

Zinc canister is the ANODEas well as the cell container

Negative Terminal

+ve

-vve

+ve

-vveZinc (ANODE)

Insulating sealant

KOH electrolyte paste

Ag2O + water paste(CATHODE)

Stainless steel casing

1100ccppiieeccee

ffoorr ssccaallee

Silver oxideButtonCells, and thedevicestheypower

Worksheet 3

Part A Fill in the Blank Spaces

The �“a)....................................... Series�” of Metals contolswhat happens when a metal reacts with the b)....................of another metal in solution. If the metal isc).......................................... the Series, it willd)......................................... the lower-activity ion from thesolution. In this process, the atoms of the higher-activitymetal e)............................... electrons, and become ions inthe solution. The process of losing electrons is called�“f)..........................................�” Meanwhile, the ions of theless-active metal g)............................. electrons and formatoms, which form a solid precipitate. The process ofgaining electrons is called h).................................................

Neither process can occur alone; each can only happenwith the other, so the entire reaction is calledi)..................................... - .......................................... or simply�“j)...............................�”

Although oxidation and reduction must occur together,they can be separated as long as k)..................................... canflow from the site of l).......................................... to the siteof m)...................................... through a wire. This is thebasis of all electrical n)...................................... and.................................................

A typical electric cell consists of 2 o)........................................In one, called the p)....................................., oxidation occurs,while reduction occurs in the q)............................. half-cell.The 2 half-cells must be connected by a conducting circuitso that r).......................... can flow from the s).........................to the t)...................................... Half-cells must also beconnected by a �“u)....................... Bridge�” to allow v)..............to diffuse between half-cells, so that the total w)...................................................... remains balanced.

The voltage (or x)............................) of a cell can bedetermined from a table of �“y)..................................................Potentials�”. Each half-reaction has been measured (underz)...................................... conditions) against a �“referencehalf-cell�”. The reference used is the aa)..................................

............................. half-reaction which has been givena value of ab).................... volts, and all other half-cellsmeasured against it.

For Galvanic Cells, when combining any 2 half-equationsfrom the table, the one ac).................................... the tablemust always by written as an ad)...............................................,and its Eo value ae)................................................... You canthen af)............................. the 2 Eo values to get the total cellag).................................. under standard conditions.

A Galvanic Cell is one which has a ah)....................... cellEMF and will run ai)............................................. whenconnected. The chemical reaction is aj)................-thermic.

The original �“ak)................... cell�” allowed the invention anddevelopment of many small, portable, electrical devices.�“al).......................................... cells�” have allowed evenfurther miniaturization.

Part B Practice problems

1. Metal Displacement ReactionsFor each combination below, firstly use the �“Activity Series�”to decide whether or not a reaction would occur.If not, write �“no reaction�”. If so,�• write half-equations for the change occurring to eachspecies. Label each half-reaction as �“oxidn.�” or �“reduction�”�• write a balanced, net ionic equation for the overallreaction.

a) Magnesium metal placed in a solution of Pb2+ ions.b) Lead metal placed in a solution of Mg2+ ions.c) Aluminium metal placed in a solution of Cu2+ ions.d) Copper metal placed in a solution of Ag+ ions.e) Iron metal placed in a solution of Ba2+ ions.f) Calcium metal placed in a solution of Sn2+ ions.

2. Galvanic CellsFor each cell diagram or description, below:i) Write half-equations for each half-cell. Label each as�“Anode reaction�” or �“Cathode reaction�”ii) Find the cell EMF under standard conditions.iii) Write an overall, balanced, net ionic equation for the cell

b) One half cell comprises an iron electrode in a solutionof Fe2+ ions. The other has a magnesium electrode in Mg2+

c) Ca|Ca2+ || Cu2+|Cu

d) An inert graphite electrode is in contact with an acid(contains H+) in a stream of H2(g). This is connected to aZn /Zn2+ half-cell.

e) The same H+/H2 half cell is connected to onecontaining a graphite electrode in a solution containing Cl-ions, and dissolved Cl2(aq)

f) (C) I-(aq)|I2 || O2, H+|H2O (C)

23






Va)

Mg

Mg22++ Cu22++

Cu

Atomic Mass Number and �“Atomic Weight�”You should recall that the mass of an atom:

Mass = sum of (protons + neutrons)Number

The mass number is always a whole number.

Any atom can be described this way:

However, on the Periodic Table, elements are described likethis:

... and the �“Atomic Weight�” is usually NOT awhole number. Now (finally) the explanation:

IsotopesYou already know that each element is composed of atomswhich are all the same as each other. Well, that�’s almost true!

All the atoms of an element have exactly the same �• number of protons�• number of electrons

It is the number of electrons, and their arrangement in theirorbits which gives each atom its chemical properties, anddefines it as a particular element.

However, the number of neutrons can vary:

Example: the Isotopes of Hydrogen

0 neutrons 1 neutron 2 neutrons

These atoms all have the same chemistry, because theelectrons are the same in each; so they are all Hydrogen.However, their Mass Numbers are different.

Most elements exist in nature as a mixture of 2 or moreisotopes. The �“Atomic Mass�” shown on the PeriodicTable is the weighted average of the mixture ofisotopes that occurs on Earth.

Example: Chlorine exists as 2 isotopes:

17 protons 17 protons17 electrons 17 electrons18 neutrons 20 neutrons

On Earth, there is a mixture of these 2 isotopes in such aproportion so that the �“average�” atomic mass is 35.45. Thisis the value of Atomic Weight shown in the Periodic Table.

Isotopes are commonly described by their individual massnumbers. The isotopes above are called �“Chlorine-35�” and�“Chlorine-37�”, or simply Cl-35 and Cl-37.

Below left are Hydrogen-1, Hydrogen-2 and Hydrogen-3.

24


4. RADIOACTIVITY & ITS USES




} = �“Atomic Number�”

+- - -nn nn

nn+ +

1111H 22

11H 3311H

Br8035

Mass Number

Atomic Number

Cl3517 Cl37

1718

ArArgon

39.95

Atomic NumberEqual to the number of electronsand the number of protons ineach atom

Chemical Symbol

Element Name

�“Atomic Weight�”NOT the �“Mass Number�”

ISOTOPESare atoms of the same element

(same Atomic Number)but with different numbers of neutrons

and different MASS NUMBERS

RadioactivityIn 1896, the French scientist Henri Becquerel discoveredthat certain minerals, containing uranium, were emitting amysterious, invisible radiation.

It was then discovered that there were, in fact, 3 differentradiations that were soon called alpha (!!), beta (&&) andgamma ('') rays, and that these were coming from thenucleus of atoms.

Alpha Radiationis a stream of particles. An alpha particle is a �“chunk�” of nucleus, made up of2 protons and 2 neutrons.

Beta Radiationis also a stream of particles,this time high-speed electrons ejected from an atomic nucleus.

Gamma Radiationis very high frequencyelectromagnetic waves, similar toX-rays, but carrying even moreenergy. Gamma radiation is often associated with theemission of alpha and beta particles.

+ nn +

e-



25

Radioactivity and Nuclear StabilityIt turns out that you can�’t have any old combination ofprotons and neutrons in an atomic nucleus... the nucleuscan only be stable if the proton-neutron ratio is withincertain, very narrow limits.

This is best seen if all the known isotopes of all theelements are plotted on a graph, as follows.

As an example, consider the isotopes of carbon:

Carbon-12, if plotted on thegraph, lies exactly on the

�“Line of Stability�”

Carbon-14 lies just above the�“Line of Stability�”, inside the�“dotted-line zone�”.

The nucleus is unstable because it has toomany neutrons, (or not enough protons) in itsneutron:proton ratio.

To achieve stability, it undergoes a Radioactive Decay toget rid of some electric charge and some energy.

In the case of Carbon-14, it emits a Beta particle andGamma energy and transmutes into a stable nitrogen atom.(Details are NOT required by the Syllabus)

Transuranic ElementsAs the graph shows, once a nucleus has more than about 80protons (and about 120 neutrons) it becomes too large tobe fully stable. There are naturally occurring elements withlarger nuclei, but they are all unstable and radioactive.

The largest naturally occuring atoms are isotopes ofuranium (Atomic Number 92), and in early text books youwill see that the Periodic Table ended at uranium. However,over the past 50 years or so, it has become possible toartificially manufacture atoms of elements larger thanuranium. These are called the �“Transuranic Elements�”.

Most Periodic Tables now list transuranic elements as far asAtomic Number 110 or even to No.118, although thenames for some of these have not been agreed upon, andin some cases only tiny quantities have ever been made, andthey are so unstable that their existence is fleeting.

Making Transuranic AtomsThe elements immediately after uranium can be made inrelatively large quantities in a nuclear reactor, by a processof neutron bombardment.

Example:If the isotope uranium-238 is placed in a nuclear reactor, itwill be bombarded by neutrons (released by the nuclearfission occurring in the reactor). A neutron will eventuallystrike the nucleus and cause the following nuclear reactions:

Uranium + neutron Neptuniumatom atom

Beyond element number 95, it is only possible to makesmall numbers of new atoms in a Particle Accelerator.Atomic nuclei are accelerated up to very high speeds bypowerful magnetic fields, and then collided so thatsometimes 2 nuclei will fuse together, such as:

Lead + Calcium Nobeliumnucleus nucleus nucleus

Recent DiscoveriesA 1999 claim for the production of element 118 has notbeen confirmed by other scientists.

In 2004, a few atoms of element 115 (temporarily namedUnunpentium) were apparently made by the reaction:



20 40 60 80 100 number of Protons

num

ber

of N

eutr

ons

20

40

60

80

100

120

14

0

lliinnee ww

hheerree

nn == pp

�“Line ofStability�”These atomsare stable

IInn tthhiiss zzoonnee,, nnuucclleeii aarree ttoooo bbiiggttoo bbee ssttaabbllee,, aannddaarree rraaddiiooaaccttiivvee

WWiitthhiinn tthhee ddootttteedd lliinnee zzoonnee,,nnuucclleeii ccaann eexxiisstt,, bbuutt hhaavvee tthheewwrroonngg bbaallaannccee ooff nneeuuttrroonnss &&pprroottoonnss,, aanndd aarree uunnssttaabbllee,,rraaddiiooaaccttiivvee iissoottooppeess

BBeeyyoonndd tthhee ddootttteedd lliinneezzoonnee,, nnoo aattoommiicc nnuucclleeuussccaann eevveenn eexxiisstt..

66pp+

66nn0

66pp+

88nn0

C126

C146

92238 U 0

1 n 93239 Np

92239 U +

&& decay

01 n + 4

82206 Pb

2048 Ca

102254 No +

95243 Am

2048 Ca

115287 Uup +



26

Commercial RadioisotopesAlthough making a few atoms of a new Transuranicelement might capture the scientific headlines, theimportant routine job of making useful, radioactivematerials goes on every day.

Australia is a non-nuclear country, but we do have onesmall nuclear reactor at Lucas Heights in Sydney. Itspurpose is research, and to prepare useful radioisotopes formedical and industrial use.

Production of Commercial RadioisotopesGenerally, the production of useful radioactive materials isachieved by placing the appropriate �“target�” atoms inside anuclear reactor and allowing neutron bombardment tooccur.

One of the most important and commonly usedradioisotopes produced is Cobalt-60. It is produced when�“ordinary�”, stable Cobalt-59 absorbs a neutron:

Uses of RadioisotopesCobalt-60 is unstable and undergoes Beta Decay:

It is the gamma radiation which makes Cobalt-60 veryuseful in a variety of roles in both medicine and industry.

By enclosing the radioactive material inside a heavilyshielded container with a narrow aperture, a narrow beamof gamma rays can be produced.

The energy carried by gamma rays can vary considerably.The radiation from Cobalt-60 is ideal for certain industrialapplications and in the medical treatment of some cancers.

Industrial Uses of Cobalt-60The gamma rays from Cobalt-60 are very penetrating, andvery destructive to living cells.

In the production of medical supplies, such as bandagesand dressings, it is vital that the product is totally sterile(germ-free). This is achieved by irradiating the productswith doses of gamma radiation high enough to destroy anybacteria or fungi spores which might be present.

In aircraft manufacture, the airplane parts may be weldedtogether. It is essential that the welded joints are totallystrong and free of defects. (Having a wing fall off in flightis not a good look this season!) To �“see�” inside the weld,gamma rays are used like X-rays; they are beamed throughthe welded joint and an image captured by a �“gamma-raycamera�”. Analysis of the image allows engineers to be sureof the quality of the welding.

Medical Uses of Cobalt-60Some forms of cancer can be treated by beaming thegamma rays into the tumour. Cancer cells are activelygrowing and this makes their DNA more susceptible togamma ray damage than healthy cells.

By focusing the beam into the tumour, and using carefullycontrolled doses of radiation, it is possible to destroycancer cells with minimal damage to healthy tissue.

Why is Cobalt-60 Ideal for These Uses?

�• Cobalt-60 has a half-life of 5.3 years, so once a cannisteris prepared, it will have a useful life of about 6-10 yearsbefore it needs to be replaced. This is convenient forindustrial and medical uses.

�• The energy of the gamma rays emitted by Cobalt-60 isideal for the imaging of welded metal joints, and for killingliving cells, whether tumour cells or bacteria on a bandage.

�• It is relatively cheap and easy to prepare Cobalt-60 byinserting �“ordinary�” Cobalt-59 into a nuclear reactor andallowing neutron-bombardment to occur.



In a nuclear reactor there isa constant �“flux�” ofneutrons.When one collides with thenucleus it may �“stick�” andcreate a new isotope of thatelement

2759 Co 0

1 n 2760 Co +

2760 Co 0

-11 e 2860 Ni + + ''

&& particle gammaelectron ray

''




27

Detection of RadiationThe Alpha, Beta and Gamma radiations from radioisotopescan be detected in various ways.

�• Photographic Film is �“exposed�” by these radiations, andcan be used to detect it. (This was how radioactivity wasfirst discovered.)

�• The �“Geiger-Counter�”, or Geiger-Muller Tube is anelectronic device which detects radiation because of theionization it causes.

Radiation causes electrons to be knocked out of theirorbits, so the atom becomes an ion. One alpha paticle canionize thousands of atoms, causing a tube of non-conducting gas (Argon is often used) to becomemomentarily conductive.

An electronic circuit detects the change and �“counts�” theionization events occurring when radiation is present.

�• A Scintillation Counter detects radiation by the flash oflight which some chemicals emit when struck by radiation.Light-sensitive detectors pick up each tiny flash of lightand an electronic circuit counts and records the events.

Benefits and Problems of the Use of Radioisotopes

Some practical uses of radioisotopes were described on theprevious page.

Benefits�• Using gamma rays to check the quality of a welded jointis the only way to ensure quality, without breaking the jointopen to inspect it visually. X-rays will not penetrate themetal well enough; only the penetrating nature of thegamma rays makes this possible.

The benefits to air safety should be obvious.

�• Using gamma rays to sterilize bandages is cheaper andmore effective and reliable than the alternatives whichinclude heat treatments and/or chemical antiseptics.

�• The use of gamma ray therapy for certain cancers issometimes the best option in cases where surgery and/orchemotherapy are not appropriate. Medical professionalshave found that there are positive benefits in terms oftreating the disease.

ProblemsThe problems associated with the use of radioisotopes,centre mainly around the safety of the people who workwith the radioactive materials.

All radiations are dangerous to living cells, and even low-level exposure is known to increase the risk of geneticmutations and development of cancers.

From the workers at the nuclear reactor, to those whohandle and transport the isotopes, to the professional end-users in hospitals or industry, there are risks of dangerousexposure to radiation.

The key to safety is effective packaging and shielding of thematerial, and constant monitoring for escaped radiation.For example, all personnel in �“at-risk�” jobs andenvironments must wear small �“tell-tale�” detectors to warnof radiation exposure.

Use of a Radioisotope Related to ChemistryThe syllabus requires that you are able to explain the use ofradioisotopes in terms of their chemical properties.

A good example is the use of Iodine-131 in the medicaltreatment of thyroid cancer. The thyroid gland is located inthe throat, and produces a vital hormone which has iodineatoms in it.

This gland is the only part of the body which uses iodine,and enzymes in the gland are able to chemically �“recognize�”iodine ions and very efficiently �“harvest�” iodine from theblood stream.

Iodine-131 is radioactive and emits beta and gamma rays.

ThyroidGland

If a small amount of I-131 isinjected into a patient who has atumour in the thyroid gland, theradiation level is so low that thereis little risk to their healthy tissue.

However, due to the chemistry ofthe iodine, the thyroid glandrapidly absorbs the isotope andconcentrates it. The radiation isconcentrated in the �“targetorgan�” and is very effective indestroying the tumour.

I-131 has a short half-life and theradiation disappears rapidly.

ElectronicCounter

GeigerTube

Worksheet 4

Fill in the blanks

Isotopes are atoms of the samea)........................................ which have the sameatomic b)..................................., but differentc)............................................... because they have adifferent number of d).................................. in thenucleus. Most elements occur in nature as amixture of 2 or more e)...........................................

The �“Atomic Weight�” shown on the periodictable is the �“weighted f).........................................�”of the masses of the mix of isotopes in nature.

Isotopes of an element show exactly the sameg)..................................... properties, but some maybe unstable and h).....................................................There are 3 different radiations that might beemitted:

�• i).............................. (!) radiation is a stream ofparticles. Each particle is composed ofj)................................... and ........................................�• Beta radiation (symbol, k).................) is a streamof l)...........................................�• m).................................. (') radiation isn)....................-frequency waves.

Whether or not any isotope is stable orradioactive is mainly determined by the ratio ofo).............................. to ..................................... inthe nucleus, and also how large the nucleus is. Allatoms with more than about p).............. protonsare too big to be stable.

The largest naturally-occurring atoms are of theelement q).................................... which has atomicnumber r)............. Atoms larger than this arecalled �“s)........................................ Elements�” andare all made artificially by either t)............................- bombardment in a nuclear reactor, or bycolliding different nuclei in au).................................... .........................................

Commercial Radioisotopes can also be preparedby neutron- v)........................................ in aw).............................. .................................... One ofthe most commonly used radioisotopes is Cobalt-x)...................., which is unstable and decays byemitting y)................... and ........................ rays.

It is used in industry forz).......................................... medical bandages anddressings, and for checking the quality ofaa)................................................. in aircraftmanufacture. In medicine, it is used to treatab)...................................... by killing the tumourcells with ac)............................ rays.

The radiations from radioactive substances canbe detected and measured byad)....................................... film, as well as the�“ae).................................-Counter�” whichelectronically registers the af)....................................effects of the radiation. Another method ofdetection, called a �“ag............................. -Counter�”,detects the ah)..........................................................which some chemicals emit when struck byradiations.

The benefits of using radioisotopes are related toeach specific use. The problems associated withradioactive materials are mainly linked to theai)............................... of personnel who work withthem.

28








29 www.keepitsimplescience.com.au


PPRROODDUUCCTTIIOONNooff

MMAATTEERRIIAALLSS

CONCEPT DIAGRAM (�“Mind Map�”) OF TOPICSome students find that memorizing the OUTLINE of a topic

helps them learn and remember the concepts and important facts.Practise on this blank version.

Practice QuestionsThese are not intended to be "HSC style" questions, but tochallenge your basic knowledge and understanding of thetopic, and remind you of what you NEED to know at theK.I.S.S. Principle level.

When you have confidently mastered this level, it isstrongly recommended you work on questions from pastexam papers.

Part A Multiple Choice

1.If propene (C3H6) underwent an addition reaction withwater, the correct structural formula for the product wouldbe

2.Alkenes can be identified by their reaction with brominewater, in which the bromine:A. moves from one liquid layer to the other.B. changes colour from brown to purple.C. completely loses its colour.D. changes from colourless to purple.

3.In the �“Catalytic Cracking�” of the alkane C20H42, themolecule happened to break up into 4 pieces; 1 molecule ofethylene, one of octane, 1 of hexene, and anotherhydrocarbon molecule. The formula for the 4th fragmentwould be:

A. C4H8 B. C6H12 C. C2H4 D. C3H8

4.An �“addition polymer�” is formed when:A. long-chain alkane molecules combine.B. C=C double bonds are formed in monomer molecules.C. molecules join by removing atoms to create bonds.D. monomers join by splitting C=C double bonds.

5.In general terms, increasing the size and mass of any �“sidegroups�” in an ethylene-based plastic, will probably result inthe plastic beingA. softer and more flexible.B. less soluble in water.C. a better conductor of electricity.D. harder and more rigid.

6.Cellulose is:A. an addition polymer of ethylene.B. a condensation polymer of glucose.C. an addition polymer of glucose.D. a monomer which can be polymerized.

7.Theoretically, we should be able to use cellulose as a rawmaterial to replace petroleum compounds. However, thereis one technology lacking which prevents this becoming aneconomically viable process. The step missing is a cheapefficient way to convert:A. cellulose into glucose.B. glucose into ethanol.C. ethanol into ethylene.D. ethylene into plastics.

8.The alkanol with condensed structural formulaCH3(CH2)4CH2OH would be called:A. butanol B. pentanol C. hexanol D. heptanol

9.The alkanols have much higher m.p.�’s & b.p�’s compared tothe corresponding alkanes, because:A. the mass of the OH group increases dispersion forces.B. the intra-molecular covalent bonds are stronger.C. the O-H bond is polar, creating a dipole.D. the C=C double bond is much stronger than C-C bonds.

10.As well as a source of carbohydrates and some live yeast,the other necessary conditions for the production ofethanol by fermentation are:A. temperature above 40oC and plenty of oxygen.B. anaerobic conditions and temperature below 20oC.C. temperature around 25oC and plenty of oxygen.D. anaerobic conditions and temperatures about 25oC.

11.Which equation for the combustion of methanol is the onefor which the energy released would be equal to #Hc ?

A. CH3OH(g) + 2O2(g) CO2(g) + 2H2O(g)

B. CH3OH(l) + 3O2(g) CO2(g) + 2H2O(l)2C. 2CH3OH(l) + 3O2(g) 2CO2(g) + 4H2O(l)

D. CH3OH(g) + 3O2(g) CO2(g) + 2H2O(g)2

30





A. B.

C. D.

H H HH

HHHH CC C

H HH

HHHH CC C

O-HH

H HH

HHH CC C

O-HH

O-HH

H HH

HHH CC C

O-HH




12.Which of the following is NOT a reason to considerethanol as a fuel to replace petrol?A. Ethanol is a higher energy fuel than petrol.B. Ethanol is a renewable and sustainable resource.C. Ethanol is potentially �“Greenhouse friendly�”.D. The technology to produce ethanol is already known.

13.If each of the following metals were placed into a solutionof copper(II) sulfate, which one would NOT react?A. silver B. zincC. iron D. magnesium

14.

In the cell shown:A. electrons would flow towards the Mg half-cell.B. zinc would be oxidized by the reaction.C. positive ions would flow out of the Mg half-cell.D. the zinc half-cell is the anode.

15.The Galvanic Cell shown in Q14 uses a metal and ions ofthe same metal in each half-cell. If you built a series ofsimilar cells, but used different metal combinations in eachcase, which of the following would give the highest cellvoltage? (Assuming all other variables were kept the same.)A. iron & zinc B. copper and silverC. copper and magnesium D. magnesium and zinc

16.In the following equation, which species has undergonereduction?

Cl2(aq) + 2Br-(aq) Br2(aq) + 2Cl-(aq)

A. Cl2(aq) B. Br-(aq)

C. Br2(aq) D. Cl-(aq)

17.Isotopes haveA. the same mass number as each other.B. different atomic numbers.C. different electron configurations.D. the same chemical properties as each other.

18.In order to manufacture atoms of Meitnerium (elementnumber 109) a suitable method might be:A. neutron bombardment of uranium atoms.B. allow radioactive decay of element No.110.C. collision of lead & cobalt atoms in a particle accelerator.D. chemical addition reaction of uranium & chlorine.

Longer Response QuestionsMark values shown are suggestions only, and are to give youan idea of how detailed an answer is appropriate.

19. (3 marks)Using structural formulas, show the addition reactionbetween ethylene and hydrogen bromide (HBr). Show thereactants and product(s). You do not need to name anycompounds.

20. (4 marks)Explain, using chemical equation(s) when needed, whyliquid hexene will de-colourize a bromine solution, butliquid hexane will not.

21. (6 marks)The main industrial source of ethylene is �“Cat-Cracking�” ofcertain molecules in petroleum.a) Outline the general process of �“Cat-Cracking�”, includingthe meaning of the term.b) Outline the process of �“Addition Polymerization�” ofethylene.c) Draw a structural formula for a section of a polyethylenemolecule containing 3 monomer units.

22. (7 marks)A common plastic is known as P.V.C.a) Draw a structural formula for the monomer from whichPVC is made, and give both its common name andsystematic chemical name.b) Account for the differences in properties and typicaluses of PVC compared to polyethylene.

23. (4 marks)The amino acid �“Glycine�” has the following structure:

The condensation polymer �“polyglycine�” can be formed byjoining together many glycine molecules.

a) Use structural diagrams to show the 2 products formedwhen two glycine monomers join together.

b) Explain why this is called �“condensation�”polymerization.

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V

Mg

Mg22++ Zn22++

Zn

O-HH

O

CH

H

H H

N C

24. (9 marks)a) Describe the structure of the cellulose molecule,including the name of the monomer.b) Explain why cellulose can be considered a �“renewable�”resource.c) Write symbol equations (including catalysts) tosummarize the reaction

i) of glucose to form ethanol.ii) of ethanol to form ethylene.

25. (5 marks)a) Describe in general terms, the differences in theproperties of solubility in water, and m.p. & b.p., betweenthe alkanes and the alkanols.

b) Account for these differences in terms of the intra-molecular and inter-molecular bonds in each type.

26. (6 marks)As part of your studies you have carried out an experimentto produce ethanol by fermentation.

a) List the chemical substances placed in the reaction flask.b) Describe the conditions used to promote the reaction.c) List the significant observations made over several daysof the reaction occurring.d) As part of the experiment, you will have monitored anymass change. State the result, and explain the change.e) What process was (or may have been) used to collectrelatively pure ethanol.

27. (8 marks)Using the equipment shown, the �“Heat of Combustion�”of methanol was measured experimentally.

Results�• Mass of methanol burnt = 0.58g�• Mass of water in can = 100g�• Change in temperature ofwater in can = 14oC

a) Write a balanced, symbolequation for the completecombustion of methanol.b) Calculate the amount of heatenergy captured by the water inthe can.c) Assuming 100% efficiency inthis �“calorimeter�”, calculate theHeat of Combustion for methanol

i) per gram. ii) per mole.d) Explain why this value is unlikely to agree closely withthe �“text-book value�”.

28. (6 marks)Assess the potential of ethanol as an alternative fuel,including discussion of the advantages and disadvantagesof its use.

29. (10 marks)a) Write a net ionic equation for the reaction which occurswhen a piece of magnsium metal is dropped into a solutionof lead(II) nitrate.b) Write 2 separate �“half-equations�” for the reaction, andlabel each as either �“oxidation�” or �“reduction�”.c) Sketch a galvanic cell which could be set up (using simplelaboratory equipment and appropriate chemicals) whichwould use the same reactions described in part (a) & (b).Label the �“anode�”, �“cathode�” and �“salt bridge�” and showthe direction of electron flow in the external circuit.d) Determine the value of the cell voltage under standardconditions.

30. (6 marks)Solid copper metal reacts with a solution containingmolecular chlorine (Cl2(aq)) to form chloride ions andcopper(II) ions, both in solution.a) Write a balanced equation (including states) for thereaction described.b) State the �“oxidation number�” for each species in theequation, and hence state which species has been oxidizedand which has been reduced.c) Write half-equations for the reaction, and calculate thecell voltage which would be produced if this reaction wasused in a Galvanic cell under standard conditions.

31. (6 marks)The ordinary dry cell (Leclanche cell) and the silver oxide�“button cell�” both use exactly the same anode reaction, butdifferent cathode reactions.a) Write a half-equation for the anode reaction of bothcells.b) Choose either of the cells mentioned above and write

i) the cathode half-equation.ii) the overall cell equation.

c) Discuss the impact of each of these cells on society, andtheir relative cost and practicality.

32. (10 marks)a) What are �“isotopes�”?b) What, in general terms, determines whether an isotope isstable or radioactive?c) List the 3 types of radioactive emissions, and for eachstate what it is.d) Describe a method for making �“Transuranic�” elements.

33. (3 marks)Identify 3 different instruments or processes that can beused to detect nuclear radiations.

34. (5 marks)a) Indentify one use of a named radioisotope in industry.

b) Identify one use of a named radioisotope in medicine,and explain how its use is related to its chemical properties.

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