Production of Materials - AceHSC · Production of Materials 1. Fossil fuels provide both energy and raw materials such as ethylene, for the production of other substances 1.1.2 Identify

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Production of Materials

1. Fossil fuels provide both energy and raw materials such as ethylene, for the

production of other substances 1.1.2 Identify the industrial source of ethylene from the cracking of some of the fractions from the

refining of petroleum

- Crude oil is a form of a fossil fuel. It is a complex mixture of hydrocarbons consisting mainly of alkanes and

smaller quantities of other hydrocarbons such as alkenes.

- The fractions of petroleum can be separated through a process called FRACTIONAL DISTILLATION.

- In this process the crude oil is heated which results in the weak dispersion forces between hydrocarbon

molecules to be broken. Light fractions with lower boiling points (weak rise higher in the fractionating

column. Heavier fractions with higher boiling points are collected from lower in the column.

- The larger and less useful products of the fractional distilling process can be broken into smaller and more

useful molecules (smaller length chains) through a process referred to as CRACKING.

- Two types:

1. It is a process in which the higher molecular weight (high boiling point) fractions from crude oil are broken down

into lower molecular weight (lower boiling point) hydrocarbons (just 2 molecules, an alkene and alkane).

2. This process usually occurs under high temperatures and pressures (slightly above atmospheric pressure) and

in the absence of air.

3. Catalysts known as zeolites (fine

porous, aluminosilicates) are used

which allow slightly lower

temperatures (5000C) and pressures

to be used.

4. Process occurs in a cat cracker.

5. This process uses less heat than

THERMAL cracking, but it cannot

decompose large molecules completely

into ethylene, so it is insufficient in meeting the demands of the industry. E.g. Cracking of pentane into

ethylene and propane:

Used mostly in Aus and USA where natural gas is used

1. It is the main method of ethylene production and does not use a catalyst only very high temperatures.

2. In this process low economic hydrocarbons such as ethane (C2H6), which is obtained from natural gas, is mixed

with steam and passed through hot (700°C to 1000°C) metal coils at pressure above atmospheric.

3. The alkanes are decomposed completely into ethylene and other short chains.

4. The steam removes carbon deposits from the metal coils. The heat from the coils breaks bonds to change the

ethane or larger hydrocarbons to ethylene.

5. Steam is used as it allows for easy flow of hydrocarbon gasses and it dilutes the mixture to create smooth

reactions

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

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1.1.3 Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into

many useful products

- Ethylene contains a double bond in its structure

- The high reactivity of this double covalent bond allows ethylene to be chemically transformed into a wide

variety of useful products.

- Halogens or compounds containing highly electronegative

elements(such as chlorine, bromine and oxygen) are attracted to

the double bond and electrons are transferred as they react.

- They react with the double bonds due to the high electron cloud

density at this site.

- The electron density of a double bond makes ethylene very

reactive.

- The most characteristic reaction with ethylene is the addition reaction where one of the bonds in the double

bond breaks open and an atom is ‘added’ or bonded with each of the carbon atoms

- Some products formed from ethylene include

o Polyethylene (CH2) – used as a plastic

o Ethanol (C2H5OH) – used as a disinfectant

o Ethanoic Acid (CH3COOH) – used as a food preservative

1.1.4 Identify that ethylene serves as a monomer from which polymers are made

- Polymerisation is the chemical reaction in which many identical small molecules (MONOMERS) combine to

form one very large molecule (POLYMERS).

- Due to the presence of a very reactive double bond in ethylene, it can be readily involved in polymerisation

- During the reaction the double bond of the monomer is broken in order to form the polymer chain.

- It is the starting material for many important polymers

CH2 = CH2 CH2 = CH2 CH2 = CH2 CH2 = CH2 CH2 = CH2

- CH2 - CH2 - CH2 - CH2-

1.1.5 Identify polyethylene as an addition polymer and explain the meaning of this term

- Polyethylene is an ADDITION POLYMER

- An Additional Polymer forms when small molecules (monomers such as ethylene) adding together without

the loss of any atoms to form large molecules (polymers)

- In an addition polymerisation reaction, no additional molecules (e.g. water) are produced – there is no gain

or loss of atoms, the double bond simply ‘opens’ and monomers attach.

- The double bond ‘opens up’ to form single bonds with neighbouring molecules

- The monomers simply add to the growing polymer so that all the atoms present in the monomer are also

present In the polymer

Double bond in ethylene opens

up in addition polymerisation

to allow monomers to join with

each other

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LDPE

•Extensive Branching disrupt regular, linear packaging of chains - soft

•Low MP compared to other macromolecules due to weak dispersion forces

• Produced under high temp 300C. and pressure 1000-3000 atm

•Small amount of oxygen peroxide required as intiator

HDPE

•Reduced branching allows linear packaging which increases dispersion forces resulting high MP - hard

• Produced under low temp 60oC. and pressures 1000atm

•Process occurs in Hydrocrabon solvent

•Uses an ionic catalyst, the Ziegler-Natta catalyst, a mixture of compounds such as TiCl4 and Al(C2H5)3.

1.1.6 Outline the steps in the production of polyethylene as an example of a commercially and

industrially important polymer

Polyethylene is an example of a commercially and industrially important polymer. There are 2 main types: Low

Density Polyethylene (LDPE) and High Density Polyethylene (HDPE).

There are 3 main steps in the production of Polyethylene and they are the same for both LDPE and HDPE.

1. Initiation

In this first or radical formation step, the initiator molecule is decomposed by heat into an active species which is a

free radical (a molecule with one unpaired electron). The initiator molecule is added to the ethylene container; in

the diagram below, it is usually peroxide molecule as it contains an easily breakable O – O bond which is usually

degraded by heat. E.g. degradation of benzoyl peroxide

The initiator reacts with one ethylene molecule, breaking its double bond, and attaches to only ONE bonding site,

creating an ethylene-initiator RADICAL. The “dot” represents a free, highly reactive, electron. Radicalised initiator

may also be called In.

Heat

Where n is a very large

number

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2. Propagation

Another ethylene monomer attaches to this radical, opening another bonding site, then another attaches, and so on,

rapidly increasing the length of the chain creating a larger free radical chain. One of these reactions:

Repeating this reaction many times gives a general formula:

3. Termination

The reaction stops (terminates) when two such chains collide and the two radicals react, forming a longer chain. This

is a random process, so the length of polyethylene chains can vary greatly. (The peroxide initiator is eventually

engulfed by the reaction, and so is no longer present at termination). Chemists have also developed techniques to

halt the growth of a chain at particular lengths.

1.1.7 Identify the following as commercially significant monomers (vinyl chloride and styrene) by both

their common and systematic name:

Vinyl Chloride:

It is a very commercially significant monomer

– SYSTEMATIC NAME: Chloroethene

– COMMON NAME: Vinyl Chloride

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– FORMULA: C2H3Cl or CH2=CHCl

– It is an ethylene molecule with one of its hydrogen atoms substituted with a chlorine atom.

– It can form polyvinyl chloride (PVC), a very important polymer.

– Diagram of polyvinyl chloride:

Styrene:

SYSTEMATIC NAME: Phenylethene, Ethenyl benzene

COMMON NAME: Styrene

FORMULA: C8H8 or CH2= CHC6H5

Styrene is an ethylene molecule with one of its hydrogen atoms replaced

by a benzene ring.

o A benzene ring is a six-carbon ring with alternating double-bonds.

The double bonds within benzene are not reactive; but the double

bonds in alkenes are reactive.

It forms polystyrene which is a polymer

Diagram of polystyrene:

1.1.8 Describe the uses of the polymers made from the above monomers in terms of their properties

Polystyrene

2 main types of polystyrene are commercially manufactured: crystal polystyrene and expanded polystyrene. Crystal

polystyrene is a clear amorphous polymer that exhibits high stiffness and good electrical insulation properties.

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– Crystal Polystyrene:

Uses Related to Properties:

o CD cases and cassette tapes; used because polystyrene is clear, hard, rigid, easily shaped, and is a

good insulator.

o Screw driver handles and kitchen cupboard handles; very durable and strong, hard and inflexible.

o The stiffness results from the presence of the large benzene rings that are attached along the

polymer chains. This high stiffness makes the polymer suitable for rigid items like car battery cases

and handles for screwdrivers and other tools.

– Expanded Polystyrene:

Expanded polystyrene is white and has good heat and sound insulation properties. It can be produced by blowing

gases through molten polystyrene and then allowing it to cool.

Uses Related to Properties:

o Packaging, and disposable cups and eskies; it is light (full of air), cheap, and it is a thermal insulator

o Rigid polystyrene foam is an important product in protective packaging, which accounts for up to 15%

of its use.

o Sound-proofing; it is a shock absorbent material, light, easily shaped

o Low Density nature allows it to be used in surf boards

– Polyvinyl Chloride (PVC):

Uses Related to Properties:

o Garden hoses; since pure PVC breaks down in ultraviolet light it contains UV absorbers (e.g. titanium

oxide) which prevents UV decomposition allowing it to be used outdoors; it is relatively un-reactive,

flexible, and durable.

o Can be softened with plasticisers which decreases the dispersion forces between the polymer chains

and thus making the polymer more flexible allowing it to be used for surgeon gloves

o Pipes and guttering; it is very rigid and hard, and un-reactive. It is also easily shaped.

o PVC is impervious to oils and most organic materials and so can be used to make bottles and other

packaging to hold these materials

1.2.2 Identify data, plan and perform a first-hand investigation to compare the reactivities of

appropriate alkenes with the corresponding alkanes in bromine water

AIM: To perform a firsthand investigation to compare the reactivities of appropriate alkenes with the corresponding

alkanes in bromine water

EQUIPMENT:

Hexane, 1-Hexane, Cyclohexane and cyclohexane in dropper bottles

5 clean, dry, medium sized test tubes

5 test tube stoppers

Test tube rack

Bromine water (BrOH) in dropper bottles

Safety goggles

VARIABLES

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Controlled: Size of test tube – Amount of hydrocarbon and bromine water used – shaking of test tubes in same way

– corresponding alkanes – Corresponding alkane and alkene used with similar structure differing only in

absence/presence C=C double bond.

Independent: Alkane or alkene added

Dependent: Reactivity of alkane/alkene, colour change during the experiment

SAFETY:

Wear safety goggles to avoid Hexane, 1-Hexane, Cyclohexane , cyclohexane and bromine water from splashing

into eyes as they are corrosive and mildly poisonous. Can also cause eye damage (bromine water)

Hydrocarbons and bromine water must be kept away from sparks and flames as they are flammable

Due to the corrosive properties of the chemicals being used, gloves should be worn to prevent burns resulting

from prolonged skin contact.

Bromine fumes are very poisonous and are able to cause eye and throat irritations. The experiment should be

conducted in a fume cupboard or test tubes must be stopped

METHOD:

1. Conduct in the absence of UV lights

2. Place 4/5 medium sized test tubes, precleaned into a test tube rack

3. Using a clean measuring cylinder, add 5ml of bromine water into each of the test tubes and record initial

colour

4. Add 5ml of hexane using a clean 10ml measuring cylinder into one of the bromine water test tubes.

5. Stopper the test tubes with a test tube stopper

6. Gently shake the test tube and record the colour change in the test tube

7. Repeat steps 4-6 with 5ml of hexane, cyclohexane and cyclohexene with the remaining bromine water test

tubes

8. 1 bromine water test tube should be left and this will act as the control

9. Repeat the experiment 10 times and if similar results are obtained then the experiment can be deemed

reliable

RESULTS

Alkene decolourised the bromine water, changing it from to colourless. Alkanes however did not decolourise

the water the bromine water.

Hexene – C6H12 (l) + Br2 (aq) C6H12Br2 (aq) 1, 2 – dibromohexane

Cyclohexene – C6H10 (l) + Br2 (aq) C6H10Br2 (aq) - 1, 2 – dibromocyclohexane

This is because the double bond in the alkene is able to undergo an addition reaction with the bromine water to

decolourise it from to colourless. Alkanes however cannot undergo an addition reaction as they are saturated

and do not contain a double bond. They can undertake a substitution reaction which in the presence of UV light can

take days to complete.

DISCUSSION

Validity – There was an independent and dependant variable being tested. The quantities were constant and the

equipment was similar. It could be improved by using more and a wider range of alkanes and alkenes

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Reliability – The experiment can be deemed reliable as the experiment was repeated by other class members and

similar results were obtained

Accuracy – The results were qualitative rather than quantitative, however a measuring cylinder was used

CONCLUSION

The reactivities of appropriate alkenes were much higher than those of the corresponding alkanes as shown by their

tests in bromine water using cyclohexane, cyclohexene, hexane and hexene.

1.2.3 Analyse information from secondary sources such as computer simulations, molecular model kits

or multimedia resources to model the polymerisation process

MODELLING POLYMERISATION

METHOD

1. Construct one initiator molecule (containing an O – O bond in R – O – O – R)

2. Construct 10 monomer units (CH2 = CH2 )

3. Decompose the initiator molecule (by breaking the O – O bond to create two free radicals (R-O.)

4. React one of the free radicals with the first monomer. The double bond is broken as the free radical initiator

adds onto the molecule. An activated monomer forms ROCHCH.

5. The activated monomer then combines with a further ethylene molecule and the process continues until it

has attached to 5 monomer units

6. Use the other RO. Radical to repeat steps 4-6 with the other monomers

7. Using the two polymer chains, react their free ends to make one long chain with the RO groups at either end,

modelling termination

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2. Some scientists research the extraction of materials from biomass to reduce our

dependence on fossil fuels 2.1.1 Discuss the need for alternative sources of the compounds presently obtained from the

petrochemical industry

There is a strong need for alternative sources of compounds presently obtained from the petrochemical industry.

The petrochemical industry refers to all the chemicals derived from the components of crude oil. Two of the major

products of the petrochemical industry are fuels and polymers. Humans have used petroleum in many areas,

including fuel.

2C8H18 (l) + 25O2 (g) 16CO2 (g) + 18H2O (l)

Furthermore the petrochemical industry includes all commercial polymers, such as PVC. Polyethylene is created from

the addition polymerisation of ethylene (ethene). The double bond of ethene is opened by an initiator radical

allowing the radical to join to the ethylene molecule. This then creates a monomer radical which then combines with

other ethylene monomers creating a chain. When two chains collide into each other the radicals react stopping

further addition of monomers as there are no free bonding sites. This process can be summarised by: where n is a

large

number

Polyethylene is a very tough, flexible and durable polymer used for sandwich bags, cling wrap, car covers, squeeze

bottles, freezer bags, water pipes, wire and cable insulation. Similarly polyvinylchloride is created from the addition

polymerisation of vinyl chloride molecules. An initiator molecule breaks open the double bond present between the

carbon atoms allowing the radical to bond with the monomer. This radical monomer then bonds with other

monomers creating a chain. When to chains collide into each other the radicals react stopping further addition of

monomers as there is no free bonding sites. This process is summarised in: where n is a very large number

Uses of PVC include pipes and clothing. The world’s crude oil sources are unfortunately finite and are expected to

last another 50 – 100 years.

There is a great need for alternative sources of compounds presently obtained from the petrochemical industry

POINTS FOR POINTS AGAINST

1. World’s crude oil supplies are expected to last another 50 – 100 years after which they will run out. Crude oil is also a fossil fuel, and thus they are non-renewable.

1. Alternative sources such as biomass may be used however they are more expensive than crude oil to use as a source in production of materials

2. Particular petrochemical products such as petrol lead to the formation of pollutants such as CO (through incomplete combustion) which have negative impacts on the respiratory health of the population.

2. New infrastructure needs to be constructed (such as fermentation plants for ethanol), a process which takes time and money.

3. If crude oil runs out before alternative sources are developed then there will be less plastics, food will be more expensive, conflict and countries dependent on crude oil may possibly collapse.

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2.1.2 Explain what is meant by a condensation polymer

1. Condensation polymer’s form through condensation polymerisation.

2. Condensation polymerisation is the process in which two monomers (of different functional groups) combine

(link together) with the elimination of a smaller molecule such as water.

3. It is also called Step growth polymerisation. Often one monomer is a dicarboxylic acid and the other monomer is

a diamine or a diol.

4. E.g. Cellulose, Rayon, Nylon

2.1.3 Describe the reaction involved when a condensation polymer is formed

1. Condensation polymerisation involves a reaction between two functional groups in which a molecule of water

(or some other small molecule) is eliminated and the two functional groups become linked together.

2. Condensation polymerisation usually involves a reaction between two different monomers, but can occur

where a molecule contains two different functional groups.

3. The most common type of condensation polymerisation occurs between monomers containing a carboxylic acid

group (–COOH) and either an alcohol (–OH) or an amine group (–NH2). Many natural polymers such as cellulose,

starch, glycogen, silk, wool and proteins, and synthetic polymers such as nylon, polyethylene terephthalate

(PET) and Kevlar, are formed by condensation polymerisation.

Cellulose (C6H10O5) is a natural polymer formed through the polymerisation of a monomer; glucose, which can be

written as OH - C6H12O6 – OH. When two glucose monomers join through hydroxyl groups (-OH), an H-OH molecule is

condensed out, leaving an -O- linking the two molecules

As can be seen, the reaction sites are the hydroxyl (OH-) groups on the first and fourth carbons (C-1 and C-4). Each

glucose molecule has 2 reaction sites; that is why it can polymerise.

One C-OH bonds to another C-OH, forming a C-O-C bond (glycosidic bond).The left over H+ and OH- combine, forming

water.

The glucose monomers join to form a cellulose molecule after losing water in the condensation polymerisation

process.

C6H12O6 + C6H12O6 2C6H10O5 + H2O

n(C6H10O5) n(C6H1206) + n-1(H2O)

2.1.4 Describe the structure of cellulose and identify it as an example of a condensation polymer found

as a major component of biomass.

Cellulose is a naturally occurring condensation polymer (a biopolymer) made of the

monosaccharide monomer glucose.

It is the single most abundant polymer on Earth, making up about 50% of the total

biomass of the planet (biomass is the mass of all organisms in a given area).

CONDENSATION REACTIONS ADDITION REACTIONS

Both involve monomers bonding together to form a long chain molecule

No double bonds necessary Monomer has a double bond which breaks during polymerisation

Polymer forms and also another smaller molecule No small molecule produced

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There are two structural forms of glucose called alpha-glucose and beta-glucose. It is the beta form that leads to

cellulose formation.

Cellulose is a very long polymer containing about 2000 to 8000 glucose molecules in long chains. These

glucose molecules are strongly linked together by covalent bonds.

Hydrogen bonding between the chains as well as strong dispersion forces, due to their large molecular

weight makes cellulose chains linear, rigid, strong and resistant to chemical attack. The glucose molecules

alternate in the chain and every alternate one is inverted

The close packaging of these strands/ribbons and the strong hydrogen bonding and dispersion forces

between them give cellulose its strength and rigid structure.

Contains 1,4 β linkages resulting in the formation of flat ribbon like strands. Beta-glucose monomers link

together by a beta 1,4-glycosidic bond

Cellulose is also insoluble in water because its structure exposes few OH (hydroxy) groups to the water

molecules. These properties are why plant cell walls are made of cellulose and this is why cellulose is found

as a major component of biomass.

2.1.5 Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals

and discuss its potential as a raw material

The BASIC carbon-chain structures that are used to make petrochemicals are carbon-hydrogen bonds such as those

present in ethylene (2C), propene (3C) and butene (4C). Glucose, the basic structure in cellulose, is a 6C molecule.

Hence it has to potential to be transformed into the above compounds. Also being a major component of biomass, it

is readily available, renewable, and environmentally viable. Cellulose structure has three carbon-chain and four

carbon-chains present with glucose monomer units and attached hydrogen and hydroxy groups. These basic carbon-

chain structures can be changed to be a raw material for production of petrochemicals.

IDENTIFY: Cellulose has a strong potential as a raw material.

DESCRIBE: The petrochemical industry consists mostly of polymers and fuels. These substances contain basic carbon-

chains which are also present in cellulose. How cellulose is made (draw it and possible equation), describe current

petrochemicals and how they are used (fuels and polymers) and how cellulose contains basic carbon structures to

allow it to be used for these purposes

ADVANTAGES DISADVANTAGES

1. More environmentally viable as the source is

renewable and easily available

1. Conversion of cellulose to ethylene is very expensive

2. The basic C structures are in cellulose which are

required to make petrochemicals

2. Large amounts of fertile land would be required to

produce quantities of cellulose to meet the needs of the

population

3. Cellulose can be used as a raw material by first

converting it to an ethylene

3. Fossil fuels are currently much cheaper to produce

that biomass fuels. Considerable energy is needed to

plant, fertilise, harvest and process energy crops.

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4. Cellulose also exists in waste plant matter from

agricultural matters and products. Disposing these

wastes creates problems and is expensive. Using them

to form petrochemicals would be ideal

4. Deforestation of land must take place, and that land

would not be used for food production increasing food

prices.

5. Cellulose can be converted into ethanol which can then be used as fuel

5. Converting cellulose to glucose is difficult

2.2.1 Use available evidence to gather and present data from secondary sources and analyse progress in

the recent development and use of a named biopolymer. This analysis should name the specific

enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential

use of the polymer produced related to its properties.

IDENTIFY

Has a strong potential use

DESCRIBE

What is a biopolymer:

Biopolymers are polymers which are produced by living organisms or are produced using chemical reactions to

process a starting material which has been produced by a living organism. E.g. starch and proteins

Name of the biopolymer:

BiopolTM

Name of the organism:

Ralstonia eutrophus (formerly Alcaligenes Eutrophus)

Production of the biopolymer

Polyhydroxybutytrate (PHB) is a type of biopolymer. PHB combines with polyhydroxyvalerate (PHV) to form

polyhydroxyalkanoate (PHA); biopol. It is a co polymer, as it consists of 2 monomers, 3 – hydroxybutytrate, 3 –

hydroxyvalerate.

Biopol is produced by placing Alcaligenes Eutrophus in a medium in which it can multiply (excess carbon in the form

of glucose). A nutrient is then restricted (nitrogen) and the microorganism no longer multiplies but produces the

biopolymer to be stored and used for energy. From here the biopol can amount to half the dry weight of the

bacteria. The biopolymer is then purified by dissolving it in a chlorinated hydrocarbon (trichloromethane)

centrifuging to remove solid waste and precipitating the final product solution and drying it to form powder.

Properties

Biopol is tough, semicrystalline with a tensile strength similar to propylene, resistant to acids and bases and insoluble

to water allowing it to be used for shampoo and cosmetic package and garbage bags It is also nontoxic and

biodegradable allowing for use in disposable nappies, golf tees, razors and mulch mats. Has a high melting point of

175OC and its density is higher than that of water

Disposable containers for shampoo, cosmetics, milk bottles, etc., as it only takes 2 years to decompose back

into natural components.

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High grade biopol is also being developed for use as woven patches to prevent tissue scarring after surgery.

This is because it is biocompatible (does not cause adverse reactions in the body) and biodegradable (will be

absorbed into the body), nontoxic and has a high tensile strength

ADVANTAGES DISADVANTAGES 1. Biodegradable decomposes into smaller and

simpler substances naturally over time; unlike

polyethylene and other petroleum derived plastics,

and so will help to reduce levels of rubbish in land fills

1. 5 to 10 times more expensive than current polymers

2. Biopol also lacks the ability to withstand high impact

and high temperatures rendering it unusable in some

cases

2. Renewable

3. It is compatible with organisms (biocompatible); it is

not rejected by the body’s immune system and so can

be used safely

4. Non - toxic

Criteria:

The criterion for assessing biopol is the economic cost, range of use and properties, environmental reliability and

cost to the economy of a transition.

Judgement:

Biopol has a strong potential for widespread usage, due to it being renewable, biocompatible and biodegradable.

This makes is suited for use in medicine and everyday disposable materials. However continued research to

overcome economic disadvantages and improve the properties of Biopol

Analyse progress in the recent development:

There have been many recent developments in biopol> Biopol is produced from the bacterium Alcaligenes

Eutrophus. However recent genetic engineering developments have allowed bacterium such as genetically modified

E.coli to be used. This would have various advantages such as:

1. Better yield of the product

2. Faster growth

3. Easier extraction

4. Reduced production of waste biomass

5. It also meant that the bacteria can be extracted from more cost effective sources. This is mainly from whey,

molasses and common agricultural wastes. This would in effect lower the commercial cost biopol.

The first biopol produced in industry was significantly brittle. This hampered its usage in common disposable

materials and medicine. It was simply not strong enough. However it was found that an introduction of propanoic

acid into the diet of the bacteria (CH3CH2COOH) would produce a much more flexible and widely used polymer. That

is why currently the diet of the biopol producing bacteria is excessive carbon, less nitrogen and propanoic acid

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3. Other resources, such as ethanol, are readily available from renewable resources

such as plants. 3.1.1 Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process

and the catalyst used

Ethanol has an OH group meaning it can be classified as an alkanol. A dehydration

reaction is one in which water is released/ removed. The dehydration of ethanol is the

chemical process whereby a water molecule is removed from ethanol, forming

ethylene. Industrially this involved heating ethanol vapour over a catalyst at 350ºC

ethanol → ethylene + water

C2H5OH (l) → C2H4 (g) + H2O (g)

However it would usually occur as a very slow reaction, by using a catalyst we can

ensure that the yield is achieved much faster allowing for economic viability

An acid catalyst (CONCENTRATED SULFURIC ACID) is needed because the acid breaks the C-OH and C-H bonds,

allowing the formation of a double-bond and water. A catalyst increases the rate of reaction by providing an

alternate path with lower activation energy for the reaction to occur. Other catalysts include phosphoric acid or

heated ceramic solids.

1. C2H5OH + H2SO4 C2H5HSO4 + H2O

2. C2H5H2SO4 C2H4 + H2SO4

Overall dehydration: C2H5OH C2H4 + H2O

3.1.2 Describe the addition of water to ethylene resulting in the production of ethanol and identify the

need for a catalyst in this process and the catalyst used

The hydration of ethylene is the chemical process whereby a water molecule is added to ethylene, forming ethanol.

This reaction occurs in 2 stages:

1. The DILUTE SULFURIC ACID adds onto the ethylene to produce ethyl hydrogen sulfate.

C2H4 + H2SO4 C2H5HSO4 2. The ethyl hydrogen sulfate reacts with water generating ethanol; sulfuric acid is reformed.

C2H5HSO4 + H2O C2H5OH + H2SO4

Overall addition: C2H4 (g) + H2O (g) CH3CH2OH (l) ∆H = –46 kJ/mol

Basically ethylene has reacted with water to form ethanol. This reaction is carried out at 300ºC

3.1.3 Describe and account for the many uses of ethanol as a solvent for polar and non-polar substances

Ethanol is a very important industrial solvent. It is actually a polar molecule and

a polar solvent. The polar part of the molecule; the hydroxyl group (the –OH

group) forms strong hydrogen bonds and dipole- dipole interactions with

other polar molecules due to the difference in polarity. The slightly positive H

end can form weak hydrogen bonds with slightly negative oxygen, nitrogen and

flourine of an adjacent molecule. Hydrogen bonds can also form between O

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and H atoms with water allowing water to dissolve in ethanol

The ethanol molecule also contains a non-polar part, the ethyl group CH3-CH2 which assists some low molecular

weight non-polar solutes to dissolve in ethanol, allowing it to act as a solvent for non – polar molecules. This is

because of the dispersion forces ethanol can form with molecules of non-polar substances.

This is important in chemistry and pharmacy where alcohol–water mixtures are often used to dissolve various

natural oils and organic substances that are normally insoluble in water. E.g.:

This is useful in industry where often the active ingredient of cough mixtures is dissolved in ethanol, then in

water. It is also used in production of perfume.

Iodine solutions in ethanol–water mixtures have antiseptic properties. The solvent used is a mixture of

ethanol and water as non-polar iodine has only a limited solubility in water.

Ethanol or ethanol–water mixtures are also used as solvents in cosmetics and toiletries, medications, antiseptics and

perfumes. In addition, ethanol is an industrial solvent for lacquers, paints, resins, oils and fatty acids.

NOTE: IN SUCH QUESTIONS DRAW THE HYDROGEN BONDING BETWEEN ETHANOL MOLECULES

3.1.4 Outline the use of ethanol as a fuel and explain why it can be called a renewable resource

As a renewable resource:

Ethanol can be a renewable resource because it can be derived from non-fossil fuel sources, such as the

fermentation of glucose

This glucose can be derived from bacterial decomposition of cellulose (a renewable very abundant

material) or from starch (mainly from corn crops)

Ethanol is able to be used as a petrol supplement as it releases heat once combusted. Brazil uses pure ethanol in

3.5 million cars, 85%, 20% and 90% concentrations are used in other countries. Sweden has 85% ethanol. Australia,

USA and Denmark have introduced blends of 10% ethanol and 90% petrol.

Despite its short chain, ethanol is a liquid (due to strong polar bonds). This makes it an easily transportable fuel, and

thus has been used for many years for outdoor camping, hikers, etc. Due to its ability to be combusted it can be used

as a fuel.

It can be considered renewable because when it

combusts it forms CO2 and H2O.

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

The CO2 and H2O is used in plants to form

glucose through photosynthesis which can be

fermented using yeast to reform ethanol; and

as plants can be continuously regrown, ethanol

can be produced as part of this cycle. As a result

of all this ethanol is a renewable fuel as plants

can be continuously grown to produce ethanol

and so it can be continuously produced

therefore it is renewable.

However when ethanol is produced, at the end

of the process it must be distilled which

16

requires large amounts of heat which usually comes from hydrocarbons and non-renewable resources; so ethanol

cannot be considered completely renewable. Also consumption of fuel by machinery used to harvest is not taken

into consideration

Give equations of photosynthesis, fermentation and respiration

3.1.5 Describe conditions under which fermentation of sugars is promoted

Fermentation is the biochemical process in which glucose is turned into ethanol and carbon dioxide by the action of

enzymes produced by microbes (esp. yeast). The production of ethanol is promoted by certain conditions such as:

I - Inorganic nutrients such as nitrogen or phosphorus

G - Grain or fruit (sugars) to provide the glucose (must)

O - Once ethanol % reaches 15% the process stops due to alcohol poisoning of the fermenting bacteria

W - Warm temperatures between 25OC – 37OC, preferably 37OC (must)

E - Anaerobic environment exclusion of air to prevent oxidation of ethanol to Ethanoic acid

W - distilled water is optional (ideal)

E - Enzyme or catalyst such as yeast to promote the reaction (must)

P - 3.7–4.6 (low pH prevents pathogens from growing)

3.1.6 Summarise the chemistry of the fermentation process

Yeast is added to mashed grain and water.

The yeast and other microbes break down the large carbohydrates (e.g. starch or sucrose) into simple sugars

(glucose or fructose) which are then fermented.

sucrose + water glucose + fructose

C12H22O11 (aq) + H2O (l) C6H12O6 (aq) + C6H12O6 (aq)

– In an oxygen-free atmosphere, the yeast use their enzymes to break down the sugars, forming ethanol and

CO2 as products.

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

– When ethanol concentration reaches 15%, the yeast die and fermentation STOPS.

– Distillation is used to obtain higher ethanol concentrations (95-100%).

3.1.7 Define the molar heat of combustion of a compound and calculate the value for ethanol from first-

hand data

Molar heat of combustion is the amount of energy in the form of heat that is released through the complete

combustion of one mole of a substance under standard conditions (25OC and 100kPa)

First Hand Example

Initial temp of 100mL of water = 22.6 OC

17

Final temp of 100mL of water = 35.9 OC

Initial mass of spirit burner + ethanol – 235.56g

Final mass of spirit burner + ethanol = 234.23g

Specific heat capacity of water = 4.18x103JKg-1K-1

Mass of water = 100g

Molar heat of combusting 1.33g of ethanol = 100 X 4.18 X 13.3

= 5559.4 J

No. of moles in 1.33g of ethanol =

= 0.028870365

Convert to one mole =

= 192.564.24J

=193 Kj

REASONS FOR DIFFERENCE BETWEEN THEORETICAL AND DETERMINED VALUES

Heat loss to the surroundings

Conducting vessel absorbs heat

Incomplete combustion

3.1.8 Assess the potential of ethanol as an alternative fuel and discuss the advantages and

disadvantages of its use.

Ethanol has a good potential to be used as an alternative fuel.

80% of the world’s demand for transportation fuels is petroleum derived. However as issues of petroleum such as

price, availability and environmental sustainability continue to rise, the concept of other fuels as alternatives

becomes more attractive. There are many potential uses of ethanol as an alternative fuel. Ethanol is either formed

by hydration of ethane:

C2H4+ H2O CH3CH2OH

Or by the fermentation of sugar cane and other crops:

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

Due to environmental awareness, ethanol has been increasingly used as an alternative fuel either pure or in a

mixture of petroleum. Approximately 8 million vehicles worldwide run on ethanol/petrol blends.30% of Brazilian

automobiles run on at least 25% ethanol fuels. Many other countries such as China and South Africa are investing

money into researching the potential of ethanol as a fuel. The current usage of ethanol as a fuel reflects its increased

potential use as a fuel.

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ADVANTAGE DISADVANTAGE

1. Undergoes complete combustion meaning less hydrocarbons and toxic emissions

1. Up to 24% mixtures of ethanol can be used after which engine modifications must be carried out which are expensive

2. Renewable since it can be made from carbon dioxide, water and sunlight (via glucose) and when it is burnt it returns to carbon dioxide and water which can be converted to ethanol

2. In order to produce ethanol from crops to provide ethanol as an alternative fuel it would require twice the area used for farmland today (arable land).

3. Ethanol blend have increase octane rating of lead free fuels and they also have reduced CO emissions by 25% to 30%

3. In the long term ethanol has a much more aggressive effect on engine tubing and pipes than gasoline which almost acts as a lubricant

4. Returns 139% of energy invested in its production 4.Higher production costs than petroleum with less energy being released

5. Ethanol has a lower ignition temperature than petrol

6. As It burns so completely spark plugs do not have to replaced as quickly as there is less carbon build up.

Ethanol has a strong potential to be used as an alternative fuel due to its renewable nature, complete combustion,

lower ignition temperatures and higher energy returns. However more cost effective means of producing ethanol

must be developed if it is to be widely used as an alternative fuel.

3.1.9 Identify the IUPAC nomenclature for straight-chained alkanols from C1 to C8

Alkanols are a group of alkanes where one or more hydrogens have been replaced by the hydroxyl (–OH) functional

group

When naming alkanols, there are specific rules:

The number of carbons determines the prefix of the name:

#C’s 1 2 3 4 5 6 7 8

Prefix methane- ethane- propane- butane- pentane- hexane- hepane- octane-

If there is only ONE hydroxyl group, the “e” is dropped from the prefix and the suffix “-ol” is added. The

carbon the hydroxyl is on must also be stated; this is written before the prefix with a “dash”. The

carbons, depending on how long the chain is, are numbered from 1 to 8.

o E.G. This alkanol has 5 carbons, but only one hydroxyl, so its prefix is

“pentan-”, and its suffix is “-ol”. Also, the hydroxyl is on the 2nd

carbon (the number is taken either from the left OR the right; the

SMALLER number must be taken). HENCE this alkanol is 2-pentanol

o INCORRECT naming would be 4-pentanol.

If there is more than one hydroxyl group, the suffixes are (1-4):

No. of OH’s 1 2 3 4

Suffix -ol -diol -triol -tetraol

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For more than one carbon, the “e” at the end of the prefix is NOT dropped. The positions of the OH groups must be

stated. If there are 2 hydroxyls on the same carbon, then the number is written twice, with a comma in between:

o E.G. This alkanol has 6 carbons, and 3 hydroxyl groups so its prefix is

“hexane-” and its suffix is “-triol”. Also, one hydroxyl is on the 1st

carbon, while the other 2 are on the 3rd carbon. HENCE, the IUPAC

name for this alkanol is 1,3,3-hexanetriol

o INCORRECT naming would be 4,4,6-hexanetriol

3.2.1 Process information from secondary sources such as molecular model kits, digital technologies

or computer simulations to model:

- the addition of water to ethylene

- the dehydration of ethanol

Hydration Method

1. Use molecular model kits to make models of C2H4, H2O and an acid catalyst (H-OSO3H)

2. Select the ethylene and acid molecules. Break one of the bonds joining the carbon atoms and break the H-OSO3H

bond

3. Join the H atom onto the first carbon and the OSO3H onto the second carbon

4. Select the water group and break it to form a H atom and an –OH group

5. Remove the -OSO3H from the model (step 3) and using the H from the water, reform the acid molecule H-OSO3H

6. Join the –OH group onto the second carbon to form the ethanol molecule

Dehydration method

1. Use molecular model kits to construct ethanol (C2H5OH) and an acid (H-OSO3H)

2. Remove the –OH group from the ethanol molecule and break the H-OSO3H bond. Attach the H atom from the acid

with the OH from the ethanol

3. Attach the OSO3H onto the carbon atom which lost –OH to form CH3CH2HSO4

4. Remove the OSO3H group and a H atom from the molecule and create a double bond between the carbon atoms

to form an ethylene molecule

5. Join the H and the OSO3H to reform the acid catalyst H-OSO3H

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3.2.2 Process information from secondary sources to summarise the processes involved in the

industrial production of ethanol from sugar cane

1. Ca(OH)2 (aq) + H2SO4 (aq) CaSO4 (s) + 2H2O (l)

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

3.2.3 Process information from secondary sources to summarise the use of ethanol as an

alternative car fuel, evaluating the success of current usage

There are 3 main types of ethanol fuels used by countries. They consist of various concentrations of ethanol mixed

with gasoline or water.

Ethanol/Petrol Mixtures: Significant quantities of 10% ethanol are sold in some parts of Australia;

however, there has not been much success as the public holds suspicions about the effect of ethanol on

their engines. However, in other countries, ethanol/petrol mixtures are very successful. In the United

States, many states require a minimum of 10% ethanol in all fuel sold. In Sweden, 85% ethanol mixtures

are common. Brazil requires that ALL car engines are able to accept at least 25% ethanol. Thus in certain

countries, use of ethanol as a fuel is quite successful.

Pure Ethanol Fuels: “Pure” ethanol is ethanol with AT MOST 1% water. It is a very clean fuel. Engines

must be modified to deal with such high levels of ethanol. It is currently being used in Brazil and

Argentina as a complete alternative to gasoline. 4 million Brazilian cars run on pure ethanol. It has

proven to be a very efficient fuel.

Ethanol Fuel-Cells: This is still in an experimental stage; it is the proposition that fuel cells be used to run

cars; success of such a scheme is still not known.

Evaluation

Ethanol is being increasingly used as a current alternate fuel to petroleum. Brazil uses pure ethanol in 3.5 million cars

with the majority running on 25%, 85% and 90% blends. Sweden uses E85 and nations such as Australia, Denmark

and the US use E10. It is able to be produced from the fermentation of glucose:

The sugar-cane crop is harvested; the whole plant is then crushed and grinded to create a cellulose/sugar

pulp.

The pulp is heated to 100°C, and dilute sulfuric acid is

added. This hydrolyses the cellulose and sucrose into

glucose molecules.

The mixture is filtered to separate the glucose

solution from the solid residues of lignin and unbroken cellulose.

The solution is filtered again to remove solid calcium

sulfate particles.

1. Calcium hydroxide is added to the sugar solution remaining to neutralise the sulfuric acid; calcium sulfate

( a precipitate) is formed

The solid residue is further hydrolysed with stronger

acids and filtered again and the sugars are added into

the filtrate

2. The solution is then fermented by being placed

in an oxygen-free tank, warmed to 37°C, and adding

suitable yeast cultures

After 15% concentration is reached, the solution is distilled to produce high concentration industrial

grade ethanol.

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

Or the hydration of ethene:

C2H4+ H2O CH3CH2OH

And can be combusted to release energy in the form of heat:

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

ADVANTAGE DISADVANTAGE

1. Undergoes complete combustion meaning less hydrocarbons and toxic emissions

1. Up to 24% mixtures of ethanol can be used after which engine modifications must be carried out which are expensive

2. Renewable since it can be made from carbon dioxide, water and sunlight (via glucose) and when it is burnt it returns to carbon dioxide and water which can be converted to ethanol

2. In order to produce ethanol from crops to provide ethanol as an alternative fuel it would require twice the area used for farmland today (arable land).

3. Ethanol blend increase octane rating of lead free fuels and they also have reduced CO emissions by 25% to 30%

3. In the long term ethanol has a much more aggressive effect of engine tubing and pipes than gasoline which almost acts as a lubricant

4. Returns 139% of energy invested in its production 4.Higher production costs than petroleum with less energy being released

5. Ethanol has a lower ignition temperature than petrol 6. Flexible fuel vehicles have been developed which are designed to run on blends of up to E85

5. Brazil is a large nation, making it a country where it is sustainable to introduce such an idea, thus not making it practical in all parts of the world

6. As It burns so completely spark plugs do not have to replaced as quickly as there is less carbon build up.

The criteria for this evaluation is the economic aspect, environmental effects, the concentration of ethanol usable

before engine modification must occur and the effect of ethanol on the engine.

Ethanol is becoming very popular as an alternative fuel as it is renewable, completely combusting, and has many

other advantages, however technological advances must be carried out to decrease ethanol production costs and

wear and tear in engines.

3.2.4 Solve problems, plan and perform a first-hand investigation to carry out the fermentation of

glucose and monitor mass changes

Method

1. Using an electronic balance, weigh out 1.0g of yeast and add it to a clean 250mL conical flask

2. Using a mortar and pestle, grind 20g of green grapes and add it to the conical flask

3. Add a tablespoon of vegemite to the mixture and approximately 100mL of distilled water into the 250mL flask

4. Using an electronic balance record the initial mass of the flask containing all reactants

5. Half fill a 250mL beaker (cleaned with distilled water) with limewater. Using the same electronic balance, record

the mass of the beaker

6. Add a gas transferring pipe from the flask to the beaker, where it should enter the limewater beaker, 1cm below

the surface

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7. Record the initial appearance of both containers and place in a warm (27 to 37OC) area. Record the, mass and

appearance of both containers until stable results are achieved.

8. Repeat the entire experiment 10 times

Safety

Wear safety goggles to prevent eye injury from corrosive chemicals such as vegemite.

Results

Carbon dioxide was released as fermentation occurs, and turned the limewater solution hazy. Fermentation occurs

as follows:

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

And the limewater turned milky:

Ca(OH)2(aq) + CO2 (g) CaCO3 (aq) + H2O (l)

The mass of the flask decreased, the mass of the limewater beaker increased.

3.2.5 Present information from secondary sources by writing a balanced equation for the fermentation

of glucose to ethanol

3.2.6 Identify data sources, choose resources and perform a first-hand investigation to determine and

compare heats of combustion of at least three liquid alkanols per gram and per mole

Method

1. Using a 100Ml measuring cylinder, measure 200ML of distilled water

2, Place a 250Ml beaker on an electronic balance and zero the electronic balance after a stable mass is obtained

3. Add the 200mL of distilled water into the beaker and record its mass. Transfer it into a clean, 250mL conical flask

4. Using a thermometer measure and record the initial temperature of the water

5. Using the same electronic balance, find the initial mass of the burners containing ethanol, 1-propanol and 1-

butanol and record each of these masses.

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6. Set up the heating apparatus with a retort stand and a boss head and a clamp holding the conical flask on the

stand

7. Light the Bunsen burner containing the ethanol and place it in the bottom so the bottom of the flask is in contact

with the tip of the flame

8. Stir the water in the flask constantly. When the temperature of the water rises by about 20OC, turn off the Bunsen

burner and record the highest and lowest temperatures achieved by the water

10. Repeat steps 1-4 and 7-9 with the beakers containing 1-propanol and 1-butanol

11. Repeat entire experiment 10 times for more reliable results

Safety

1. Wear safety goggles to protect and prevent eye irritation if splashing of hydrocarbons occurs.

2. The spirit burners must be remained covered as they are volatile

Variables

Independent: The hydrocarbons being tested Dependent: Molar heat of combustion

Discussion

Validity – the experiment was not valid as considerable heat was lost to the surroundings. Complete combustion did

not occur and the extent of the combustion was not similar, seen through the different flame colours.

Reliability – Can be deemed reliable as the experiment was repeated and similar results were obtained

Accuracy – cannot be deemed accurate as a digital thermometer was not used

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Reductant: an electron

donor; also called a

reducing agent

Reduction: the gain of

electrons or decrease in

oxidation state

Oxidant: an electron

acceptor; also called an

oxidising agent

Oxidation: the loss of

electrons or increase in

oxidation state

4. Oxidation-reduction reactions are increasingly important as a source of energy 4.1.1 Explain the displacement of metals from solution in terms of transfer of electrons

The more reactive and active metal loses one or more of it electrons and becomes a positive ion. The electrons lost

are transferred to the ions of the less reactive metal resulting in them becoming metal atoms.

Displacement reactions are actually ELECTRON TRANSFER reactions, where one substance donates electrons to

another.

EG: When zinc metal is placed in copper sulfate solution, the zinc will displace the

copper ions, forming zinc sulfate and solid copper:

Chemical equation: Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)

Ionic equation: Zn + Cu2+ + SO42- Zn2+ + SO4

2- + Cu

Net ionic equation: Zn + Cu2+ Zn2+ + Cu

– Hence, the 2 half-equations above can be labelled as oxidation or reduction

Zn Zn2+ + 2e¯ (Oxidation; zinc LOSES electrons)

Cu2+ + 2e¯ Cu (Reduction; copper GAINS electrons)

– The species that is oxidised is the reductant (thus, zinc is the reductant)

– The species that is reduced is the oxidant (thus, copper is the oxidant)

4.1.2 Identify the relationship between displacement of metal ions in solution by other metals to the

relative activity of metals

Active metals displace less active metals from a solution of their ions. The more active metal will convert the ion of a

less active metal into a neutral atom. Basically the more active metal loses electrons and forms an ion, whereas the

ions of the less active metal gain electrons to form the metal. The greater the difference in reactivity between the

two metals, the more vigorous the reaction.

Thus, a metal on the series can displace out of solution ANY metal below it, but cannot displace any metal on top

of it.

What the ‘metal activity series’ implies:

The metals on the top are very reactive and hence LOSE electrons easily, and are thus likely to be

oxidised; most of the time they are reductants.

The metals on the bottom are very unreactive; but when they are ions, they GAIN electrons very easily,

and thus are easily reduced; most likely oxidants.

4.1.3 Account for changes in the oxidation state of species in terms of their loss or gain of electrons.

The oxidation state of an element is a measure of its degree of oxidation. The oxidation state of an atom is an

arbitrary charge or number assigned to the atom according to a set of rules. These are summarised in the table:

Category Oxidation States Examples

Elements Free 0 copper metal: OS(Cu) = 0 chlorine gas: OS(Cl) = 0

Simple Ions Charge of the ion Cu2+ ion: OS(Cu2+) = +II Cl– ion: OS(Cl–) = –I

Polyatomic Ions Sum of the oxidation states sulfate ion (SO42–):

MORE REACTIVE DISPLACES LESS REACTIVE

25

of each element must sum to the charge on the ion

OS(S) = +VI OS(O) = –II [(+VI) + 4(–II) = 2–]

Molecular Compounds sum of the oxidation states of each element must sum to zero

sulfur dioxide (SO2): OS(S) = +IV OS(O) = –II [(+IV) + 2(–II) = O]

OXIDATION

Zn Zn2+ + 2e¯

An increase in oxidation number (moving towards the positive numbers) means that electrons have been lost

showing oxidation

REDUCTION

Cu2+ + 2e¯ Cu

A decrease in oxidation number (moving towards then negative numbers) means that electrons have been gained

showing reduction

4.1.4 Describe and explain galvanic cells in terms of oxidation/reduction reactions

In a galvanic cell, to utilise the electron flow, the redox reaction is split into its two half-reactions: There are two half-

cells; OXIDATION takes place in one cell and REDUCTION in the other. Oxidation occurs at the anode, releasing

electrons and Reduction occurs at the cathode which gains electrons.

A conducting wire and salt bridge connects the two half-cells and completes

the circuit; as electrons have to flow from the oxidation cell to the reduction

cell, a flow of electrons is produced in the wire, and hence electricity is

produced.

4.1.5 Outline the construction of galvanic cells and trace the direction of electron flow

– GALVANIC CELL SET-UP:

There are two half cells, each containing a solution of the metal-sulfate; one cell contains zinc sulfate,

the other cell copper sulfate.

The ANODE consists of a solid zinc electrode in the zinc sulfate solution. This is connected by a wire to

the CATHODE which consists of solid copper electrode, which is in the copper sulfate solution.

A salt bridge, soaked in potassium nitrate solution, connects the two cells. Usually containing or

saturated in electrolyte solution (e.g. KNO3), made of filter paper or U tube; completes the circuit

allowing ions to move between each half cell

– The CHEMICAL REACTIONS:

Oxygen has an oxidation number of -2 in all compounds, except in peroxides, where it is equal to -1 (peroxide

is the anion O22-).

Hydrogen has an oxidation number of +1, except in metal hydrides, where it has an oxidation number of -1

(e.g. in sodium hydride, NaH).

26

In the zinc-sulfate cell (ANODE), oxidation is occurring, as SOLID zinc is oxidised to zinc IONS, which then

flow into the zinc sulfate solution. The electrons that are released flow into the wire:

o Zn Zn2+ + 2e¯ (Oxidation)

In the copper-sulfate cell (CATHODE), reduction is occurring, as copper IONS are reduced to SOLID

copper, when then build up on the copper electrode. Electrons are received through the wire, which

then reduce the ions:

o Cu2+ + 2e¯ Cu (Reduction)

– NOTE: The oxidation and reduction cells can be on the left OR the right, it does not matter, although

oxidation is conventionally on the right.

– As the zinc is slowly oxidised, and more zinc ions build-up, the zinc sulfate solution builds up in POSITIVE

charge (more Zn2+ than SO42-).

– Similarly, as the copper ions are reduced, the copper sulfate solution builds in NEGATIVE charge (more SO42-

than Cu2+).

– However, this will affect the flow of electrons; electrically neutral solutions are needed for optimal electricity

production. Hence the role of the salt bridge:

The salt bridge completes the circuit, but also has another function.

The salt bridge maintains electrical neutrality; this means that it keeps the charges in both the half-cells

at zero, by allowing the flow of ions.

The salt bridge is soaked in potassium nitrate solution: Thus, as the positive charge builds up in the left

cell, NEGATIVE nitrate ions migrate towards the cell to neutralise the charge; as the negative charge

builds up in the right cell, the POSITIVE potassium ions move towards the cell to neutralise it as well.

Electrons flow from anode to cathode

MUST WRITE 1MOL/LITRE IN THE BEAKER (AKA SOLUTION)

Things in drawing that are necessary

– Electrode

– Electrolyte

– Connecting wire

– Voltmeter symbol

– Flow of electrons

– Salt bridge

– Half cells

– Flow of ions

– Beaker

Reasons for variation between measured potential and

theoretical potential

Impurities in the metal

Solution may not be 1mol/L

Conditions are not the same

Connecting wire may have variable resistance

27

V

4.1.6 Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells

Galvanic cell: an arrangement of electrodes and electrolytes in which a redox reaction causes a flow of electricity;

also called an electrochemical cell half-cell: either the oxidation or reduction half of an electrochemical cell

Electrode: the metallic conducting plates of a galvanic cell, placed in an electrolyte

Anode: the electrode at which oxidation takes place. This electrode is negative in a galvanic cell.

Cathode: the electrode at which reduction takes place. This electrode is positive in a galvanic cell.

Electrolyte: a substance that releases ions when in solution or when melted and that carries an electric current

Salt bridge: an electrolyte or electrolyte gel that joins two half-cells in a galvanic cell and allows movement of ions to

maintain a balance of charges; also called an ion bridge

Half-cell: either the oxidation or reduction half of an electrochemical cell

Cell notation: Zn|Zn2+ | | Cu2+| Cu

Anode species Cathode species

Salt bridge

28

4.2.1 Perform a first-hand investigation to identify the conditions under which a galvanic cell is

produced

Method:

1. Construct a galvanic cell by using 2 different metals dipping into a solution of their own ions (electrolyte). E.g. if

the anode was zinc then the electrolyte could be Zn(NO3)2. If the cathode electrode was copper, the electrolyte could

be Cu(NO3)2.

2. Soak an 8cm strip of filter paper in KNO3 and dip it into both beakers and their electrolytes

3. Connect the anode to the cathode by using a wire from the anode to the voltmeter and then to the cathode.

4. Measure the voltage of the cell and record it as it appears on the volt meter

5. Repeat the experiment 10 times

4.2.2 Perform a first-hand investigation and gather first-hand information to measure the difference in

potential of different combinations of metals in an electrolyte solution.

The same experiment above was performed again, except a range of difference electrode electrolyte couples were

used

RESULTS:

[ Zn | Zn2+ || Cu2+ | Cu ]: TOTAL voltage = 0.4 V

[ Mg | Mg2+ || Cu2+ | Cu ]: TOTAL voltage = 0.95 V

[ Al | Al3+ || Cu2+ | Cu ]: TOTAL voltage = 0.2 V

[ Fe | Fe2+ || Cu2+ | Cu ]: TOTAL voltage = 0.5 V

4.2.3 Gather and present information on the structure and chemistry of a zinc-carbon dry cell and

evaluate it in comparison to a silver-oxide button cell in terms of: 1. Chemistry 2. Cost and practicality

3. Impact on society and 4. Environmental impact:

The Dry Cell and Silver Button Cell are both compact electrochemical cells that supply electrical energy at small

currents. The Dry Cell is composed of a thin zinc cylinder which serves as the anode, a paste of ammonium chloride

and zinc chloride as the electrolyte and a carbon (graphite) rod which serves as a cathode which also contains a

mixture of manganese dioxide. The reaction that occurs at the cathode is:

2MnO2 (s) + 2NH4+

(aq) + 2e- Mn2O3 (s) + H2O(l) + 2NH3 (g)

The reaction at the anode is:

Zn(s) Zn2+ + 2e-

The silver oxide cell however is composed of a zinc and zinc oxide anode, silver oxide cathode and a potassium

hydroxide electrolyte. The reaction that occurs in the silver button cell at the zinc/zinc oxide anode is:

Zn(s) + 2OH- ZnO(s) + H2O(l) + 2e-

The reaction that occurs in this cell at the cathode is:

V

29

Ag2O(s) + H2O(l) + 2e- 2Ag(s) + 2OH-

The dry cell produces 1.5 Volts of electricity whereas the silver oxide cell produces 1.6 Volts.

The dry cell is extremely cost effective and has a low production and consumption cost.

The dry cell is not rechargeable and is actually the lowest cost primary battery. Due to this the dry cell is

used extensively in society to power low drain appliances for eg. torches, toys and portable CD players. The

silver oxide cell actually costs 10 times more than the dry cell, and is also not rechargeable making it very

difficult to replace compared to the dry cell.

However the silver button cell has a higher volumetric

density then the dry cell and is able to deliver constant

voltage over long periods and so is very practical for use in

miniature appliances such as watches and calculators.

The silver oxide cell also has a longer shelf life of 7 years

compared to the 1.5 year shelf life of the dry cell as the dry

cell often leaks.

The silver oxide cell is also much smaller than the dry cell making it practical for use in applications where

constant replacement is not an option such as heart pacemakers.

The dry cell has had a huge impact on society as it has allowed electricity to become “portable” as electricity is

produced in the cell using a chemical reaction. This has allowed the production of low drain electric devices such as

torches and CD players along with toys, clocks and other appliances. The silver button cell has also had a large

impact on society as it has allowed “miniaturized electricity” to be

employed in the running of small appliances such as watches.

The dry cell has little environmental impact as its weak acidic paste

and reaction products are non-toxic and pose little danger when

disposed of in landfills. However in the silver button cell there are

some small environmental impacts, the cell contains expensive silver

which must be recycled after being extracted from the cell itself. The

cell also contains a caustic electrolyte in the form of potassium

hydroxide which can be dangerous to plant and animal life which

comes in contact with it. Apart from this the silver button cell does

not contain any other toxic chemicals to harm the environment.

The criterion for judging the two cells is their chemistry, cost and practicality, impacts on society and environmental

impacts.

The silver button cell and the dry cell are both cells which have problems and benefits in their different uses. They

both have also had significant impacts on society and are practical for their own uses. Both however are beneficial in

their own ways and neither is necessarily better the other as they are used and applied differently.

4.2.4 Solve problems and analyse information to calculate the potential requirement of named

electrochemical processes using tables of standard potentials and half-equations

The (electromotive force) of an electrochemical process is calculated and formed using tables of standard

potentials. If you want the value for the reverse process simply change the sign of the value. In the table of

standard potentials, a metal will displace the ions of any metal below it. Thus iron will displace Cu2+ but not Mg2+

The standard electrode potential ( ) of the standard hydrogen electrode is defined as zero volts. Therefore any

calculation of the of a galvanic cell will just be the of the half cell.

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The above cell can also be represented as: [ Mg(S) | Mg2+ || Pb2+ | Pb(S) ]:

Where Mg | Mg2+ represents a metal/metal ion couple.

The double line || represents the salt bridge

Electrode/electrolyte couples have a FIXED voltage, no matter how many moles of each substance is present.

Worked Examples

Write the net cell reaction and calculate the cell potential for the following standard galvanic cell.

Oxidation reaction: Mg(S) Mg2+ + 2e- value = 2.36 since it reverse of the process

Reduction Reaction: Pb2+ + 2e- Pb (S) value = -0.13

Net cell reaction: Mg(S) + Pb2+ Mg2+ + Pb (S)

EMF = (2.36) + (-0.13) = + 2.33V

A positive cell potential indicates that the reaction occurs spontaneously

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5. Nuclear chemistry provides a range of materials 5.1.1 Distinguish between stable and radioactive isotopes and describe the conditions under which a

nucleus is unstable

Stable isotopes are atoms with the same atomic number but a different mass number. They therefore contain a

different number of neutrons. Stable isotopes do not emit radiation. Radioisotopes (radioactive isotopes) differ from

other isotopes of an element as they have an unstable neutron to proton ratio. Their nuclei are unstable and

attempt to gain stability by emitting radiation in one 3 forms (α,β or γ). The radiation that isotopes emit usually

result in the formation of another element. Radioactive isotopes can be either natural or synthetic. In addition, the

ratio of the neutrons to protons in a radioisotope places that certain isotope outside the band of stable nuclei.

A radioisotope is unstable if its neutron: proton ratio is 1:1 for elements with an atomic weight less than 20 and 1.5:1

for elements with atomic weights greater than 82. Between 20 and 83 the ratio is approximately 1.25:1. Also any

element with an atomic number greater than 83 is unstable.

5.1.2 Describe how transuranic elements are produced

Transuranic elements are elements with atomic numbers greater than uranium; that is Z > 92 (more than 92

protons)

All transuranic elements are artificially produced.

Neutron Bombardment: This process occurs in nuclear reactors in which a specified target atom is bombarded

with neutrons to produce a radioactive species with extra neutrons in the nucleus. Due to its radioactive nature

it quickly decays by emitting mostly beta but sometimes gamma radiation. When this reaches a stable state it is

called a transuranic element. E.g. When uranium-238 is bombarded with neutrons it forms uranium-239, which

however is unstable and thus decays to form Neptunium:

This however is also unstable and spontaneously decays to form plutonium:

Fusion Reactions: This method applies to those transuranic elements with an atomic number greater than or

equal to 96. In this process a small positive nucleus or proton is accelerated in a charged particle accelerator

(also known as a cyclotron) which brings the proton or nucleus to the high speeds required to overcome the

positive repulsive force of the heavy nuclei (often of a previously made transuranic element) and fuse with

them. However through this method large quantities of transuranic elements can be produced. For example the

element hassium is produced by bombarding lead with iron:

5.1.3 Describe how commercial radioisotopes are produced

Nuclear reactors enable uranium chain reactions to occur safely releasing neutrons. These neutrons are then taken

and used to bombard target atoms to producing neutron rick isotopes (cobalt-60 and Strontium-90).Technetium

99m is produced as follows:

Another method is also utilised to commercially produce radioisotopes utilises particle accelerators (which may be

linear or circular) or cyclotrons. In this method an accelerator is utilised to speed up particles and then fire them at

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target atoms at a specified energy level in an attempt to make a radioisotopes such as Iodine-123 and Fluorine-18

which are both neutron deficient isotopes.

Major hospitals in Australia have cyclotrons to produce short lived isotopes used in medical diagnosis, prediction and

treatment or most isotopes cannot be produced to far from where it needs to be used.

5.1.4 Identify instruments and processes that can be used to detect radiation

GEIGER MULLER COUNTER

1. The Geiger Muller counter detects ionising radiation.

2. Ionising energy is high energy radiation that causes ionisation of atoms.

3. It is mostly used to detect beta particles as well as alpha particles if the source is within 2cm of the window.

4. This device consists of a metal tube filled with argon gas, connected to a power supply. As radiation enters

through a mica window, it ionises the argon gas, splitting the atoms into electrons and positive nuclei enabling

the completion of the circuit.

5. This pulse of current is sent to an amplifier which sends a stronger signal to an electronic counter which

releases a number of clicks to signify whether radiation was present and to what intensity.

SCINTILLATION COUNTER

A scintillation counter is able to detect radiation, when an atom is electronically excited by radiation.

It will give off light to return to its normal state.

This flash of light is collected and converted to an electronic pulse by a photomultiplier.

This electric pulse is counted by a counter to determine the level of radiation in an environment

Used to detect Gamma, Beta and Alpha radiation.

PHOTOGRAPHIC FILM

1. Photographic film is a sheet of plastic coated on one side with a silver halide emulsion and on the other a slow

emulsion.

2. It is usually used to monitor beta and gamma rays.

3. The higher doses of radiation will blacken the slow emulsion whereas as low doses will blacken the silver halide

emulsion, as both emulsions are sensitive to electromagnetic radiation.

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4. People whose work brings them into contact with radiation wear badges containing photographic film to

monitor their exposure to radiation.

CLOUD CHAMBERS

Mainly monitor reactions in nuclear reactors.

In them the radiation is able to interact with a cold supersaturated alcohol vapour

This vapour condenses around ions formed during the ionisation of air

Cloud like wispy trails show the path of this radiation

It works best for alpha radiation, however can also be used for beta and gamma radiation.

THERMOLUMINESCANT DOSIMETER

This form of detection usually consists of a badge containing crystals of an inorganic salt.

When these crystals absorb radiation they heat up and release the light in the form of light energy.

The intensity of the light emitted acts as an indicator to represent the intensity of the radiation present.

It is used to detect gamma and strong beta rays.

5.1.5 Identify one use of a named radioisotope in industry and medicine

- Industry: Sodium-24 is used to detect leaks in oil and water pipes

- Medicine: Technetium-99m is used to detect blood clots, constrictions and other circulation disorders as well as

detecting brain tumours and heart conditions

5.1.6 Describe the way in which the above named industrial and medical radioisotopes are used and

explain their use in terms of their properties

Sodium-24

It is added to the liquid which it flows with through the pipe.

No radiation is detected from the isotope inside the pipe however when it leaks into the surrounding soil, its

radiation may be detected.

The leak is then identified and repaired.

There are a variety of properties which make it useful for this particular use.

It has a half-life of only 15hours and so after the leak has identified, it rapidly decays leaving the liquid in the

pipe safe to use again.

It is also soluble in water, which means it dissolves in the water in the pipe, allowing it be used more

effectively

Technetium-99m

Is usually mixed with some blood serum and injected into the patients blood stream. It circulates around the

body developing higher concentrations at locations of tumours, blood clots and constrictions.

Using a gamma ray camera we are able to see this build up

It can also be used to see heart condition after a heart attack

There are a variety of properties which make it useful for this particular use.

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Technetium-99m actually has a half-life of 6 hours and so rapidly decays after use causing minimal harm to

the patient

It is also low energy gamma emitting which means it does not damage the surrounding cells

It is also able to attach onto a variety compounds in the blood enabling efficient transport around the body

It is also produced from molybdenum-99 in a transportable generator enabling use in emergencies

5.2.2 Use available evidence to analyse benefits and problems associated with the use of radioactive

isotopes in identified industries and medicine

There are many industrial and medical uses of radioactive isotopes each with a number of benefits and problems.

In industry radioisotopes such as Cobalt – 60 are used in industrial radiography to inspect metal parts and welds for

defects. There are many benefits and problems when radioisotopes used in industrial radiography.

Benefits

For example cobalt – 60 is a gamma ray emitter making it useful in the area of metals as gamma rays are the

best radiation to penetrate metals which is required in industrial radiography.

It is also low energy emitting radioisotope which makes the work environment safer for the workers who

have daily exposure to the equipment reducing radiation exposure related illnesses occurring.

Problems

However despite being low energy emitting, radiation emission still poses health risk for workers in the

vicinity of the experiment. This is a problem as it costs companies involved in industrial radioisotopes large

amounts of money to ensure safety measures are established.

Cobalt - 60’s half-life of 5.3 years also poses a problem as replacement of equipment is required more

frequently and thus causes an economical problem.

There are also other industrial uses of radioisotopes. Radioisotopes such as strontium – 90 are used in thickness

gauges to monitor thickness of sheeting such as steel.

Benefits

Isotopes such as strontium – 90 are very beneficial in that they are fairly low energy emitting which enables

thin sheets of material to absorb most of the radiation providing more accuracy in the measurement and

monitoring process.

The radioisotopes used for this purpose have fairly long half-lives. For example strontium – 90 which has a

half-life of 28 years making it beneficial economically as equipment does not have to be replaced frequently.

Problems

But despite being low energy emitting, radiation emission still poses health risk for workers in the vicinity of

the radiation. This is because radioisotopes such as strontium-90 are similar to calcium and can therefore be

incorporated into bone tissue in place of calcium thus causing cancer or leukaemia due to the radiation.

From this an economic problem arises since it costs companies involved in industry large amounts of money

to ensure safety measures are established.

There are also many different advantages and disadvantages of using radioisotopes in medicine. There are many

radioisotopes used in medicine such as Technetium - 99m used to image skeleton and heart muscle but also the

brain, lungs and numerous specialised studies.

Benefits

Technetium-99m has half-life of 6 hours which is long enough to examine metabolic processes yet short

enough to limit problems to the patient.

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Technetium – 99m is also quickly eliminated from the body and emits low energy gamma radiation that

minimises damage to tissues but can still be detected by a gamma ray sensitive camera.

Problems

Technetium- 99m must be produced in portable generator when removed from nuclear reactor which is

expensive. This means many under funded clinics and hospitals end up with no means to access such

diagnostic tools as they cannot afford it.

There is also always the problem of radiation effects on body even if there is low radiation being emitted.

For example radiation may alter structure of DNA causing problems in cell division.

5.2.1 Process information from secondary sources to describe recent discoveries of elements

In February 2004 element 115, known as Ununpentium was produced in a particle accelerator after the fusion of

Americium-243 and Calcium-48.

In 1998 German Scientists at GSI in Germany isolated a few atoms of hassium, element 108 which had a half-life of

2milliseconds and decayed rapidly. It was formed in a particle accelerator following the fusion of iron-58 and lead-

208.

On November 9th 1994 German scientists at Gesellschaft für Schwerionenforschung; GSI in Germany isolated a few

atoms of element 110, Darmstadtium, which had a half-life of 180 microseconds and so decayed rapidly. It was

formed in a particle accelerator following the fusion of lead-208 and nickel-62.

Also elements with atomic number 104, 112, 114, 116, and 118 were isolated in nuclear reactors and particle

accelerators in USA, Russia and Germany. None existed for more than a few seconds.