William Kuang

Production of Materials 1. Fossil fuels provide both energy and raw materials such as ethylene, for theproduction of other substances

• Construct word and balanced formulae equations of chemical reactions asthey are encountered

Gather and present information from first-hand or secondary sources to write equationsto represent all chemical reactions encountered in the HSC course

• Identify the industrial source of ethylene from the cracking of some of thefractions from the refining of petroleum

Industrially, ethylene is produced by the cracking [both thermal and catalytic] of variousfractions (usually naptha and LPG) from the refining of petroleum. These fractions aregenerally long chain alkanes which are unreactive. In the cracking process, ethylene isconsidered a by-product as the purpose is to produce more quantities of petrol ratherthan produce ethylene specifically. In this way ethylene is produced in large quantities. Thermal cracking and catalytic cracking are two procedures used to produce shorterchain hydrocarbons from longer chain hydrocarbons. Thermal cracking involves hightemperatures (450°-750°C) and pressures (~700kPa) without a catalyst. Whilst catalyticcracking involves lower temperatures (~500°C) and pressures in the presence of acatalyst (usually zeolites)

• Identify that ethylene, because of the high reactivity of its double bond, isreadily transformed into many useful products

Due to the high electron density of its double bond, ethylene is readily transformed intomany useful products via the addition reaction; where new atoms are ‘added’ across theopened up double bond resulting in a saturated molecule e.g. ethylene + HCl =chloroethane. Ethylene is also used to make various monomers via the substitutionreaction, which can then be used to make the corresponding polymer, e.g. ethylene intochloroethene into polychloroethene (PVC). Identify data, plan and perform a first-hand investigation to compare the reactivities ofappropriate alkenes with the corresponding alkanes in bromine water [provide a briefsummary later] Aim: To compare the reactivity of hexane with 1-hexene, and cyclohexane withcyclohexene using bromine water. Safety: Wear safety glasses. Br water is corrosive (avoid contact and use droppers,clean up spills immediately). Do not pour any of the liquids down the drain (collect inorganic waste bottle to await disposal by authorised personnel). Equipment: cyclohexane, cyclohexene, hexane, 1-hexene, bromine water, droppers,test tubes, test tube rack, plastic film Method:

1. Block out all sources of light. (Controlled variable)2. Place 4 test tubes in test tube rack.3. Add 4 drops bromine water in 1 test tube. Add 8 drops cyclohexane.

Stopper test tube with plastic film. 4. Shake test tube for 1 minute (Controlled variable). Place back in test tube

Equipment: cyclohexane, cyclohexene, hexane, 1-hexene, bromine water, droppers,test tubes, test tube rack, plastic film Method:

1. Block out all sources of light. (Controlled variable)2. Place 4 test tubes in test tube rack.3. Add 4 drops bromine water in 1 test tube. Add 8 drops cyclohexane.

Stopper test tube with plastic film. 4. Shake test tube for 1 minute (Controlled variable). Place back in test tube

rack and allow layers to separate. Record observations (Dependantvariable).

5. Repeat steps 3-4 with cyclohexene, hexane, 1-hexene (Independentvariable-saturation)

Results:CACWBW = Colour After Contact With Bromine WaterCyclohexane (Colourless)-CACWBW: brown/red (a physical reaction; Br dissolving in cyclohexane)-Decolourises amber bromine water: no-2 distinct layers-No chemical reaction Cyclohexene (Colourless)-CACWBW: colourless-Decolourises amber bromine water: yes-2 distinct layers

(1,2 – dibromocyclohexane) Hexane (Colourless)-CACWBW: brown/red (a physical reaction; Br dissolving in hexane)-Decolourises amber bromine water: no-2 distinct layers-No chemical reaction 1- Hexene (Colourless)-CACWBW: colourless-Decolourises amber bromine water: yes-2 distinct layers C6H12 (l) + Br2 (aq) ® C6H12Br2 (aq) 1,2 – dibromohexane ===================================================================

- Bromine molecules are more soluble in hexane/cyclohexane than water bythe observation that the clear hexane/cyclohexane turned a red/browncolour when in contact with the amber coloured bromine water, which alsoturned a lighter shade of amber. This is due to the non-polar nature of thebromine which is more soluble in non-polar cyclohexane and hexane thanpolar water.

- Alkanes react slowly by the process of substitution- Alkenes react readily by the process of addition- In this experiment, a positive reaction is indicated by the bromine solution

turning colourless- This experiment is destructive as double bonds are broken in a chemical

reaction and products cannot be easily converted back into reactants. Controls: Blocking out sources of light (alkanes don’t react in the absence of UV light,with UV light they form free radicals), using the same equipment, quantities, temperatureand degree and period of agitation. Validity of Method: In distinguishing between alkanes and alkene, the method is validso long as it was carried out in the absence of UV light and results were recorded andcompared after a short time interval. Conclusion: 1-hexene is more reactive than hexane and cyclohexene is more reactivethan cyclohexane. (Alkene is more reactive than the corresponding alkane)

with UV light they form free radicals), using the same equipment, quantities, temperatureand degree and period of agitation. Validity of Method: In distinguishing between alkanes and alkene, the method is validso long as it was carried out in the absence of UV light and results were recorded andcompared after a short time interval. Conclusion: 1-hexene is more reactive than hexane and cyclohexene is more reactivethan cyclohexane. (Alkene is more reactive than the corresponding alkane)

• Identify that ethylene serves as a monomer from which polymers are made Ethylene serves as a monomer (a molecule that joins up with others to form a polymer)for the formation of the polymer polyethylene via the addition polymerisation process. Analyse information from secondary sources such as computer simulations, molecularmodel kits or multimedia resources to model the polymerisation process

• Identify polyethylene as an addition polymer and explain the meaning of thisterm

Polyethylene is an addition polymer – a polymer formed by the addition polymerisationprocess in which unsaturated monomers combine via addition reactions (the opening upof the double bond) to form the polymer without losing any atoms or forming any otherproducts.

• Outline the steps in the production of polyethylene as an example of a

commercially and industrially important polymer [POSSIBLE FIX] LDPE is produced using high temperatures (~ 300°C) and pressures (1000 – 3000atmospheres) with an initiator (such as peroxide) During the initiation step, the initiator is decomposed into free radicals (with U.V light orheat). These free radicals add across the double bond of an ethylene monomer viaaddition reactions to create a monomer free radical. The monomer free radical continues to react with ethylene monomers during thepropagation step. This process continues until it is stopped with another initiator molecule duringtermination.

• identify the following as commercially significant monomers:-vinyl chloride-styreneby both their systematic and common names

Vinyl chloride (common name), chloroethene (systematic name) (C2H3Cl)

Styrene (common name), ethenyl benzene (systematic name) (C8H8)

• Describe the uses of the polymers made from the above monomers in

• Describe the uses of the polymers made from the above monomers in

terms of their properties Polyvinylchloride (PVC)

- Pipes / guttering / credit cards: (hard, brittle/non-flexible, water resistant,UV absorber additive needed as PVC breaks down in UV light, pigmentcan be added to make visually appealing, heat stabiliser additive as PVChas low M.P)

- Electrical conduit / electrical coating: (electrical insulator, hard,

brittle/non-flexible, UV absorber additive) - Food packaging: (moderately resistant to chemical attack, UV absorber

additive) - Flexible hoses / gloves: (plasticiser additive needed to increase flexibility,

UV absorber additive, pigment additive) Polystyrene (PS)

- Car battery cases / tool handles: (high stiffness, lightweight, electricalinsulator, butadiene monomer can be added to increase impactresistance) [crystal form]

- Insulated food packaging: (moderately resistant to chemical attack,

good heat insulation, lightweight) [expanded form]

- CD packaging / drinking glasses: (high refractive index, high stiffness,lightweight) [crystal form]

- Protective packaging: (soft, flexible, lightweight) [expanded form -

formed by blowing gases into molten PS] PVC and PS are stiffer than PE because a chlorine atom and benzene ring are present. 2. Some scientists research the extraction of materials from biomass to reduceour dependence on fossil fuels.

• Discuss the need for alternative sources of the compoundspresently obtained from the petrochemical industry

ISSUE- Currently, deriving plastics and fuels from crude oil provides a cheap and

abundant source.- Reliance on fuel and plastics has grown. Current source is from crude

oil/petroleum. This gives power to nations that have an abundance (e.g.Iraq).

- Non-renewable. Millions of years are required to form petroleum products.In the last few decades the rate of consumption has increased dramatically.Some predict oil supplies to run out within a few decades.

- Rising cost of fuels (petrol, diesel)- Pollutants. The production of plastics and the burning of fuels contribute to

the greenhouse effect. A decreased quality of air.- Need to look for alternatives such as biomass/organic matter to reduce these

effects. Currently the compounds obtained from the petrochemical industry, namely plastics andfuels, come mainly from crude oil. This has the advantage of providing a cheap and abundant

Some predict oil supplies to run out within a few decades.- Rising cost of fuels (petrol, diesel)- Pollutants. The production of plastics and the burning of fuels contribute to

the greenhouse effect. A decreased quality of air.- Need to look for alternatives such as biomass/organic matter to reduce these

effects. Currently the compounds obtained from the petrochemical industry, namely plastics andfuels, come mainly from crude oil. This has the advantage of providing a cheap and abundantsource of useful products. However there is a need to find alternative sources as the relianceon fuels and plastics in our everyday life has grown and created a host of problems. The overreliance on crude oil has placed nations such as Iraq in a position of power and conflict.Crude oil itself is non-renewable, taking millions of years to form, and as such is in limitedsupply. With the increased rate of consumption in the past few decades, some predict oilsupplied to run out within 2-3 decades. As supplies dwindle, cost dramatically increases asseen in the early stages of rising fuel prices (petrol, diesel). The production of these products(fuels and plastics) also significantly contributes to greenhouse emissions and so does theburning of fuels. Thus the need to develop alternative sources is brought about by the overreliance on finite crude oil and the need to lessen these problems. Such alternative sourcesinclude ethanol and biomass/organic matter.

• Explain what is meant by a condensation polymer A condensation polymer is a polymer (long chain molecule) formed by a reactionbetween two functional groups of adjacent monomers, where a small molecule iseliminated (e.g. water) and the two functional groups link together. A condensation polymer is a polymer formed by the elimination of a small molecule (e.g.water) when pairs of monomer molecules join together.

• Describe the reaction involved when a condensation polymer isformed

In the formation of a condensation polymer, adjacent pairs of monomers undergo achemical reaction whereby the functional groups of the two monomers eliminate a smallmolecule (e.g. water) and the two monomers make a chemical bond in place of thefunctional groups. *NOTE: Thus in order to form a polymer in this way, each monomer must have at least 2functional groups. –COOH (carboxylic acid group), -OH (alcohol group), -NH2 (aminegroup)

• Describe the structure of cellulose and identify it as an exampleof a condensation polymer found as a major component of biomass

Cellulose is a condensation biopolymer formed by β-glucose monomers. It is a long, flat,rigid, and linear molecule, up to 10 000 glucose units long. During condensationpolymerisation, water is condensed and β-glucose monomers are linked. It is the majorcomponent of biomass (organic plant matter).

• Identify that cellulose contains the basic carbon-chain structures needed tobuild petrochemicals and discuss its potential as a raw material

In cellulose, each glucose unit has 4 carbon atoms joined together in a chain. Thus itcontains the basic carbon chain structure needed to make starting molecules forpetrochemicals (e.g. ethene, propene, butene). Cellulose has the potential to be a significant raw material in the production ofpetrochemicals. The main advantage of using cellulose is that it is in such large supply(being the major component of biomass and the most abundant polymer in thebiosphere). Also cellulose is a renewable resource and this would reduce the reliance onfinite crude oil. However its main disadvantage is that it is not economically viable to be

In cellulose, each glucose unit has 4 carbon atoms joined together in a chain. Thus itcontains the basic carbon chain structure needed to make starting molecules forpetrochemicals (e.g. ethene, propene, butene). Cellulose has the potential to be a significant raw material in the production ofpetrochemicals. The main advantage of using cellulose is that it is in such large supply(being the major component of biomass and the most abundant polymer in thebiosphere). Also cellulose is a renewable resource and this would reduce the reliance onfinite crude oil. However its main disadvantage is that it is not economically viable to beused in this way. This is because there is no cheap, efficient way to break cellulose intoglucose. Use of cellulose would also require the clearing of the natural environment. Itsuse as a raw material for petrochemicals is possible, however, with current technologies,not economically viable. Use available evidence to gather and present data from secondary sources and analyseprogress in the development and use of a named biopolymer. This analysis should namethe specific enzyme(s) used or organism used to synthesise the material and anevaluation of the use or potential use of the polymer produced related to its properties

Polylactic Acid Progress PLA was initially discovered in the 1890’s, however the first low molecular weightpolymer of lactic acid was only made in 1932. The process for its synthesis waspatented in 1954 however due to the relatively high cost of obtaining the monomer littlefurther research and development was conducted until the 1980’s. It was in 1987-92 thatCargill Inc. (USA) developed a pilot plant for its production later commercializing thepolymer in 1997. By 2002 the Nebraska and Iowa facilities were producing largecommercial quantities of PLA from corn starch. Specific enzymes or organisms used to synthesise. Microorganisms such as Lactobacillus bacteria or certain fungi such as Rhizopus oryzaeare used to produce lactic acid (via fermentation) from sugar. A.eutrophus bacteria areused to convert lactic acid into PLA. Starch (from e.g. corn) ® Dextrose is processed from the starch ® lactic acid viafermentation, Lactobacillus bacteria ® polylactic acid via condensation reactions,A.eutrophus bacteria used as a catalyst

Evaluation of the use or potential use related to its properties. PLA is currently used for a various number of applications. Being biodegradable it isused in the preparation of bioplastic, which is used in compost bags and disposabletableware. Being oil and grease resistant, it is used for loose-fill packaging as well asfood packaging. Also possessing a high tensile strength, it finds current use in numerousbiomedical applications, such as sutures, stents, dialysis media and drug deliverydevices. Also as PLA is produced from renewable resources (e.g. corn, starch) it itself isrenewable. Being biodegradable it does not remain in landfills for extended periods (e.g.centuries) like other plastics (e.g. polyethylene).

food packaging. Also possessing a high tensile strength, it finds current use in numerousbiomedical applications, such as sutures, stents, dialysis media and drug deliverydevices. Also as PLA is produced from renewable resources (e.g. corn, starch) it itself isrenewable. Being biodegradable it does not remain in landfills for extended periods (e.g.centuries) like other plastics (e.g. polyethylene). 3. Other resources, such as ethanol, are readily available from renewableresources such as plants

• Describe the dehydration of ethanol to ethylene and identify theneed for a catalyst in this process and the catalyst used

C2H5OH(g) ® C2H4(g) + H2O(g) Ethanol is converted to ethylene by a chemical reaction known as dehydration. Thereaction is carried out at around 180°C and concentrated sulfuric acid (or phosphoricacid) is used as a catalyst (to lower the activation energy) and dehydrating agent.

• Describe the addition of water to ethylene resulting in theproduction of ethanol and identify the need for a catalyst in thisprocess and the catalyst used

C2H4(g) + H2O(g) ® C2H5OH(g) Ethene is converted to ethanol by a chemical reaction known as hydration. In thisprocess ethene and water undergo an addition reaction which is catalysed by dilutesulfuric acid (or phosphoric acid). The catalyst is required as water by itself will not ‘openup’ the double bond of ethene. It is also used to lower the activation energy. Process information from secondary sources such as molecular model kits, digitaltechnologies or computer simulations to model

➢ the addition of water to ethylene➢ the dehydration of ethanol

• Describe and account for the many uses of ethanol as a solventfor polar and non-polar substances

Ethanol is widely used as a solvent in the preparation of food colourings, perfumes andantiseptics.

• Describe and account for the many uses of ethanol as a solventfor polar and non-polar substances

Ethanol is widely used as a solvent in the preparation of food colourings, perfumes andantiseptics. Ethanol is able to act as a solvent for both polar and non-polar substances because ofits molecular structure. Ethanol is soluble in polar substances (e.g. water) due to thepolar nature of its hydroxyl group (-OH). This end of the molecule interacts with otherpolar molecules and forms hydrogen bonds or dipole-dipole forces. Ethanol is also soluble in non-polar substances (e.g. oils, resins) due to the non-polarnature of its ethyl chain (C2H5). This end of the molecule interacts with other non-polarmolecules and forms dispersion forces. Process information from secondary sources to summarise the processes involved in theindustrial production of ethanol from sugar cane Sugar Cane → Crushed and mixed with water → Yeast is added and air excluded → Kept at ~37°C → Enzymes produced by yeast catalyst reactions to turn sugars (starch, sucrose) into glucose → Enzymes (from yeast) catalyze reaction to turn glucose into ethanol and CO2 → 15% ethanol solution is produced → fractionally distilled to produce a 96% ethanol solution

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

Combustion of ethanol in the presence of oxygen is an exothermic reaction. As itreleases energy, it can be used as a fuel source. Petrol containing up to 15 % ethanolcan be used in ordinary petrol engines without any modifications. Ethanol is considered a renewable resource as it can be produced from renewablesources (via fermentation) such as sugar cane. In this process glucose (formed by CO2

and water via photosynthesis) is converted to ethanol and then burnt as a fuel toproduce CO2 and water, which returns to the photosynthesis cycle. Process information from secondary sources to summarise the use of ethanol as analternative car fuel, evaluating the success of current usage As an alternative car fuel, ethanol possesses numerous advantages and disadvantagesin its use. Its advantages include being able to safely use it in up to 15% blends withpetrol in most modern cars without modification. Also as ethanol undergoes morecomplete combustion, it produces less emissions as it is burnt (e.g. CO). Australia’s E10(10% ethanol) also has the benefit of having 97% the energy of petrol alone. Being arenewable resource (via fermentation), it would reduce the dependency of finite crudeoil. However its disadvantages include not being able to use in blends greater than 15%without modification to cars. Being a solvent, it can potentially result in early deteriorationof rubber and metal components. Also by itself, ethanol produces only 30% the energyof petrol which has the added effect of requiring more production and transportation,adding to its economic and environmental impact. The success of current usage is steadily increasing as groups increasingly advocate itsuse, such as Australia’s Canegrowers and as fuel prices continue to rise. As of nowethanol as a fuel is largely limited to use as a petrol extender. However as a fuel byitself, nations such as Brazil has had particular success in introducing it as an alternativefuel, however faced large challenges from its introduction.

• Describe conditions under which fermentation of sugars ispromoted

The success of current usage is steadily increasing as groups increasingly advocate itsuse, such as Australia’s Canegrowers and as fuel prices continue to rise. As of nowethanol as a fuel is largely limited to use as a petrol extender. However as a fuel byitself, nations such as Brazil has had particular success in introducing it as an alternativefuel, however faced large challenges from its introduction.

• Describe conditions under which fermentation of sugars ispromoted

➢ Water provides the moist environment yeast need to

survive➢ Yeast catalyst which contains enzymes (to catalyse the

reaction)➢ Low O2 concentration (as fermentation is an anaerobic

process)➢ Alcohol concentration <15% as greater concentrations

typically kill the yeast➢ A warm temperature (~ 37ºC) to accelerate the

fermentation process. Excess heat needs to be dissipatedin order to prevent yeast from dieing.

• Summarise the chemistry of the fermentation process

Enzymes (biological catalysts) in the mixture convert any starch or sucrose in themixture into glucose, and then other enzymes convert glucose into ethanol and carbondioxide.

Solve problems, plan and perform a first-hand investigation to carry out the fermentationof glucose and monitor mass changes Aim: To monitor mass changes during the fermentation of glucose Safety: Wear safety glasses (to avoid materials coming into contact with the eyes).Handle breakable glass equipment with care by ensuring that a firm hold is on glasswarewhen moving around. Sweep up and dispose of any shattered glass. Method: 1) Place the following into a conical flask: 1g yeast, 20mLglucose solution (10% w/v). Stopper the flask (with rubberstopper and gas delivery tube) and weigh the apparatus(initial mass).2) Prepare a test tube filled with 30mL of limewater and place in a test tube rack. Placethe other end of the gas delivery tube into the test tube so that it is immersed inlimewater.3) Place this set-up in an incubator set at 35°C.4) Reweigh the flask after 2 days. Observe and record any changes to the glucosesolution and the limewater.5) Repeats steps 1-4 without yeast as a control (Independent variable). Compare valuesand observations between the two set-ups (Dependant variable – mass changes).6) Compare results with other groups performing a similar investigation. Results: Analysis: Over the period of the investigation the mass of the apparatus with yeastdecreased. This was due to the chemical reaction taking place where the glucose, withyeast as a catalyst, was converted to ethanol and carbon dioxide. The carbon dioxidegas escaped from the flask resulting in a decrease in mass.

The presence of the carbon dioxide was confirmed by the observation of a milky whiteprecipitate forming in the originally colourless limewater.

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

yeast as a catalyst, was converted to ethanol and carbon dioxide. The carbon dioxidegas escaped from the flask resulting in a decrease in mass.

The presence of the carbon dioxide was confirmed by the observation of a milky whiteprecipitate forming in the originally colourless limewater.

Ca(OH)2(aq) + CO2(g) → CaCO3(s) +H2O(l) In contrast to the apparatus without yeast (the control), the initial and final masses werevery similar (/…..difference). Also in the control the appearance of the mixture did notchange over the two days whereas in the non-control it did; appearance of bubbles, paleyellow colour, odour produced. The appearance of the limewater also remainedcolourless indicating that no carbon dioxide was present and that the glucose solutiondid not undergo fermentation. Conclusion: The mass of the apparatus decreased over time during the fermentationprocess due to the conversion of glucose into CO2 and H2O whereby the CO2 escapedfrom the flask. The enzymes produced by the yeast were determined as beingnecessary in the fermentation process. Present information from secondary sources by writing a balanced equation for thefermentation of glucose to ethanol

• 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 heat liberated when one mole of the substanceundergoes complete combustion with oxygen at 100 kPa and 24.79ºC, with the finalproducts being carbon dioxide (CO2) and water (H2O). The molar heat of combustion is apositive value, whereas the enthalpy of combustion is a negative value.

Molar heat of combustion ( ) was calculated using the following formula:

Where:

- m = mass of H2O- c = Specific heat capacity of H2O- Dt = change in temp of H2O after a known amount of ethanol is burnt.

Ethanol = 1364 kJmol-1

• Assess the potential of ethanol as an alternative fuel and discuss the

advantages and disadvantages of its use Currently, as an alternative fuel by itself, the potential use of ethanol is not good. As analternative fuel it has the advantages of being renewable (being formed from renewablesources) thus reducing the dependence of non-renewable crude oil. As it also undergoesmore complete combustion, its widespread use could slow the increase of air pollutantssuch as CO and SO2. Its production also has the potential to be ‘greenhouse neutral’ ifthe energy used is renewable for distillation and cultivation. However its main disadvantage is that it is not economically viable. Widespread usewould require agricultural land specifically devoted to growing suitable crop whichdramatically increases costs as opposed to using only waste product. Such additionaluse of land would have the additional effect of soil erosion, deforestation, and salinity.Production being ‘greenhouse neutral’ is also unlikely with current technologies as non-renewable resources (e.g. coal) are needed for fertilisation, cultivation and distillation tomeet a growing demand. Also by itself, ethanol produces only 30% the energy of petrolwhich has the added effect of requiring more production and transportation, adding to itseconomic and environmental impact. For these reasons, ethanol is more likely to be used as a ‘petrol extender’ as blends of

dramatically increases costs as opposed to using only waste product. Such additionaluse of land would have the additional effect of soil erosion, deforestation, and salinity.Production being ‘greenhouse neutral’ is also unlikely with current technologies as non-renewable resources (e.g. coal) are needed for fertilisation, cultivation and distillation tomeet a growing demand. Also by itself, ethanol produces only 30% the energy of petrolwhich has the added effect of requiring more production and transportation, adding to itseconomic and environmental impact. For these reasons, ethanol is more likely to be used as a ‘petrol extender’ as blends ofless that 15% can be used in current cars without modification and Australia’s E10 blendpossesses 97% the energy of petrol. However in the more distance future, when crudeoil supplies are reduced to the point that it is no longer economically viable, alternativesources of fuel such as ethanol become favourable.

• Identify the IUPAC nomenclature for straight-chained alkanols from C1 toC8

o locate longest unbranched carbon chaino name ending determined by principle function groupo number the carbons in the longest chain so that the principle function group

gets the lowest numbero Name and number all other functional groups.o For multiples of the same function group use prefixes like di- tri- tetra- etc.

(do no drop the ‘e’, such as in methanediol.)o List other functional groups in alphabetical order

Identify data sources, choose resources and perform a first-hand investigation todetermine and compare heats of combustion of at least three liquid alkanols per gramand per mole

Aim: To determine and compare heat of combustion values ( ) for methanol,ethanol, and 1-propanol by measuring and processing calorimetry data. Safety: Wear safety glasses. Alkanols are flammable fuels – ensure that a fireextinguisher or fire blanket is at hand. Alkanols are toxic – avoid skin contact and cleanup spills and wash hands immediately.

Method:

1) 100ml of water was transferred into the conical flask. A thermometer wasimmersed in the water, and the initial temperature recorded.

2) The methanol spirit burner was weighed and its initial mass recorded3) The equipment was then set up as diagram above with the wick 2cm

below the base of the flask. The wick was then ignited4) The methanol spirit burner was allowed to heat the flask for 5 minutes,

periodically stirring, and then snuffed out. The maximum temperaturereached was recorded. (Dependant variable – temperature change ofwater)

5) The methanol spirit burner was reweighed and its mass change wasrecorded

6) Steps 1-5 were repeated with the ethanol and 1-propanol spiritburner. (Independent variable – the alkanol used)

7) Results from 5 other groups performing a similar investigation werecollected and recorded to strengthen reliability

reached was recorded. (Dependant variable – temperature change ofwater)

5) The methanol spirit burner was reweighed and its mass change wasrecorded

6) Steps 1-5 were repeated with the ethanol and 1-propanol spiritburner. (Independent variable – the alkanol used)

7) Results from 5 other groups performing a similar investigation werecollected and recorded to strengthen reliability

Analysis: The molar heat of combustion values obtained for the 3 alkanols indicatethat 1-propanol releases the most energy per mole of 1-propanol, followed byethanol and then methanol. These results are considered valid on a qualitative scaleas an identical procedure was performed on each alkanol in each group. This

indicates a trend increasing molar heat of combustion ( ) with increasingmolecular mass of the alkanol. In a quantitative sense however the results obtained are considered invalid. This isbecause the investigation does not take into account the specific heat capacity of theglass conical flask or the air within. These are significant values and the investigationcan be improved by taking these into account or by replacing the glass container withone with a known heat capacity, such as copper. The theoretical values indicate thatthe experimental results obtained are invalid (….% difference). Validity can also bestrengthened by performing a similar investigation with a different method andcomparing the two independent results. If results are similar then validity isstrengthened. Also heat escaping into the environment is another factor affecting thevalidity of the results and could have been overcome by the use of an insulatingvessel. If the wick was too close to the conical flask and black soot is observed onthe conical flask, then there was insufficient oxygen supply resulting in incompletecombustion affecting the validity of results, can be overcome by ensuring with a rulerthe distance is always 2cm. In terms of reliability the results can be considered reliable if the results are within10% error of each other. The chemical reactions taking place are:

2CH3OH (l) + 3O2 (g) → 2CO2 (g) + 4H2O (g) C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g) C3H7OH (l) + 5O2 (g) → 3CO2 (g) + 4H2O (g) Conclusion: Out of the 3 alkanols (methanol, ethanol, 1-propanol) 1-propanol had the

greatest molar heat of combustion value ( ), followed by ethanol and thenmethanol. 4. Oxidation-reduction reactions are increasingly important as a source of energy

• Explain the displacement of metals from solution in terms of transfer ofelectrons

- When a more active metal (reductant) is placed in a solution containing ions of a

less active metal (oxidant), the active metal displaces the less active metal fromsolution.

- This occurs because a more active metal atom loses electrons and becomes apositive ion (the metal atoms are oxidised to ions).

- The electrons lost are transferred to the ions of the less active metal, resulting inthem becoming metal atoms (the ions are reduced to atoms).

- Oxidation is a chemical half reaction which involves the loss of electrons (or gainin oxidation number) [OIL]

- Reduction is a chemical half reaction which involves the gain of electrons (or lossin oxidation number) [RIG]

- Oxidation-reduction reactions are also called redox or electron transfer reactions.- Reduction occurs at the cathode [RED CAT]- Oxidation occurs at the anode [AN OX]- Electrons move from the anode to the cathode- Cations move towards the cathode

- Oxidation is a chemical half reaction which involves the loss of electrons (or gainin oxidation number) [OIL]

- Reduction is a chemical half reaction which involves the gain of electrons (or lossin oxidation number) [RIG]

- Oxidation-reduction reactions are also called redox or electron transfer reactions.- Reduction occurs at the cathode [RED CAT]- Oxidation occurs at the anode [AN OX]- Electrons move from the anode to the cathode- Cations move towards the cathode- Anions move towards the anode- A reductant (reducing agent) causes reduction and itself undergoes oxidation- An oxidant (oxidising agent) causes oxidation and itself undergoes reduction

• Identify the relationship between displacement of metal ions in solution by

other metals to the relative activity of metals A more active metal (the stronger reductant) will displace a less active metal fromsolution. The more active metal is oxidised whilst the less active metal is reduced.

(Also the higher the standard potential value, the more likely the substance will bereduced)

• Account for changes in the oxidation state of species in terms of their lossor gain of electrons

Oxidation state: A real or imaginary charge on an atom which indicates its state ofoxidation. During a redox reaction, species undergoing oxidation lose electrons and increase theiroxidation state number. Species undergoing reduction gain electrons and decrease theiroxidation state number. Numbering Rules

- Elements in their elemental state have an oxidation state of 0- For monotomic ions the oxidation state equals the charge of the ion- For combined oxygen the oxidation state is -2 except in peroxides (O2

2-) where it is-1.- Hydrogen in compounds have an oxidation state of +1 when combined with non-

metals, and -1 when combined with metals- The oxidation state of a compound or polyatomic ion is the sum of the oxidation

states of all its atoms.

• Describe and explain galvanic cells in terms oxidation/reduction reactions A Galvanic cell (a.k.a. voltaic cell, electrochemical cell) is a device which is set up sothat the chemical reaction which occurs generates electricity.

- This is done by physically separating the two half reactions so that the electron flowis through an external wire, rather than being transferred through direct contact.

- A salt bridge is used to complete the circuit and to allow the migration of ions inorder to preserve electrical neutrality of the electrolytes. It is impossible to havean imbalance of positive and negative ions in solution

- In the oxidation half-cell, the anode loses electrons (becomes oxidised) and goesinto solution

- The lost electrons are transferred through the external wire towards the cathode- At the cathode, ions in solution gain the electrons and are reduced to atoms- Some cations move towards the cathode whilst some anions move towards the

anode through the salt bridge in order to maintain electrical neutrality.

- In the oxidation half-cell, the anode loses electrons (becomes oxidised) and goesinto solution

- The lost electrons are transferred through the external wire towards the cathode- At the cathode, ions in solution gain the electrons and are reduced to atoms- Some cations move towards the cathode whilst some anions move towards the

anode through the salt bridge in order to maintain electrical neutrality.

• Outline the construction of galvanic cells and trace the direction of electronflow

- Taking the above example, the apparatus is set up so that there are two half cellsphysically separated.- A salt bridge containing an electrolyte (usually KNO3 so that none of the ions insolution react with it) connects the two electrolytes.- An external wire connects the two electrodes. As zinc metal is the stronger reductant, itundergoes oxidation whereby it loses electrons and goes into solution as zinc ions. Thezinc electrode is thus the anode. - The electrons flow through the external wire towards the copper electrode (thecathode) [electron flow – anode to cathode]- At the cathode, copper ions accept the electrons and are reduced to copper atomswhich deposit on the electrode- Some of the zinc cations in the oxidation half cell move towards the cathodewhilst some of the Nitrate anions in the reduction half cell move towards theanode in order to maintain electrical neutrality. [Cations towards the cathode ~Anions towards the anode]

• Define the terms anode, cathode, electrode and electrolyte to describegalvanic cells

Electrode: The conducting terminals of a galvanic cell which connects to theexternal circuit. Anode: The negative electrode of a galvanic cell. It is the site of oxidation in the redoxreaction. Cathode: The positive electrode of a galvanic cell. It is the site of reduction in the redoxreaction. Electrolyte: A liquid that conducts electricity as a result of the presence of positive andnegative ions Perform a first-hand investigation to identify the conditions under which a galvanic cell isproduced Aim: To identify the conditions in which a galvanic cell is produced.

Perform a first-hand investigation to identify the conditions under which a galvanic cell isproduced Aim: To identify the conditions in which a galvanic cell is produced. Safety: Sulfuric acid is corrosive – wear safetyglass to avoid contact with eyes. Avoid skincontact and clean up spills immediately.

Method:

1) Set up the equipment as in thediagram right according to eachrespective trial

2) Perform the following trials:(Independent variables - combination ofelectrodes, different electrolyte)(Dependant variables – occurrence ofreaction, voltage reading)

Trial Electrode A Electrode B Electrolyte C1 Zn Cu Distilled

water2 Zn Cu 1 mole/L

NaCl3 (observechange involtage >5

min)

Zn Cu 1 mole/LH2SO4

4 (Touchbottoms of X

and Ytogether)

Zn Cu 1 mole/L H2SO4

5 Cu Cu 1 mole/L H2SO4

6 Zn C 1 mole/L H2SO4

3) If no reaction is observable, reverse the polarity of the voltmeter connection. Recordall observations. Results: Trial 1: No reactionTrial 2: 0.25V, zinc dissolves, bubbles, odour producedTrial 3: 1V – 0.9V, zinc dissolves, bubbles, odour producedTrial 4: Zinc dissolves, bubbles, odour produced, no voltageTrial 5: Copper dissolves in both electrodes, bubbles, odour produced, no voltage Trial 6: 1V, zinc dissolves, bubbles, odour produced,

3) If no reaction is observable, reverse the polarity of the voltmeter connection. Recordall observations. Results: Trial 1: No reactionTrial 2: 0.25V, zinc dissolves, bubbles, odour producedTrial 3: 1V – 0.9V, zinc dissolves, bubbles, odour producedTrial 4: Zinc dissolves, bubbles, odour produced, no voltageTrial 5: Copper dissolves in both electrodes, bubbles, odour produced, no voltage Trial 6: 1V, zinc dissolves, bubbles, odour produced, Analysis: In Trial 1 no electrolyte was present and as such no ions were present for aredox reaction to take place. Thus it can be deduced that an electrolyte is necessary forwhich the electrodes must be immersed in. Trial 4 didn’t function like trial 3 as the electrodes were touching. This ensured that theelectrons produced from the zinc anode were directly transferred to the copper cathodewhich donated electrons to the hydrogen ions. Thus no electrons flowed through theexternal wire and thus no voltage was produced. Thus it can be deduced that theelectrodes mustn’t be touching for electricity to be produced. Trial 5 consisted of two same metal (copper) electrodes. Thus both electrodes are thesource of oxidation whilst the hydrogen ions are reduced to hydrogen gas. Thus noelectrons passed through the conducting leads and thus no voltage was observable.Thus it can be deduced that two different electrode conductors are necessary. Trial 6 behaved like trial 3 as two different conducting materials were used as theelectrodes and the reduction and oxidation reactions were separated. Thus zinc wasoxidised into zinc ions and the electrons pass through the external wire towards theother electrode which donates the electrons to the hydrogen ions to form hydrogen gas. A salt bridge must connect the two electrolyte solutions. An external conducting wiremust connect the two electrodes. Remember to write chemical equations when talking about these Perform a first-hand investigation and gather first-hand information to measure thedifference in potential of different combinations of metals in an electrolyte solution Aim: To measure the difference in potential of different combinations of metals inelectrolyte solution. Safety: CuSO4, ZnSO4 MgSO4, KNO3, are harmful to the skin and eyes – wear safetyglasses, wash skin immediately if in contact with the skin. Pb(NO3)2, CuSO4, ZnSO4

MgSO4, KNO3 are harmful if ingested – keep away from food, tag all chemical containerswith appropriate identification label. Method:

Method:

1) Rub all electrodes with emery paper, rinse with water, and dry with a cleancloth.

2) Set up the equipment as in the diagram above with 50mL of 1mol/Lelectrolyte solution

3) If no voltage or reaction is observable, reverse the polarity of the voltmeterconnection.

4) Record all observations5) Repeat steps 1-4: with Cu wire as a substitute salt bridge,

with Mg electrode in 1mol/L MgSO4 in beaker 2, with Pb electrode in 1mol/L Pb(NO3)2 in beaker 2, with Mg electrode in 1mol/L MgSO4 in beaker 1 with Pb electrode in 1mol/L Pb(NO3)2 in beaker 1 with Mg electrode in 1mol/L MgSO4 in beaker 1, Pb electrode in 1mol/L Pb(NO3)2

in beaker 2 (Independent variable – metal electrode in electrolyte pair combinations)(Dependant variable – voltage reading)

Results:Trial Beaker 1 Beaker 2 Observations

1 Zn + 1mol/L ZnSO4 Cu + 1mol/L CuSO4 0.3V2 (Cu wire assubstitute salt bridge)

Zn + 1mol/L ZnSO4 Cu + 1mol/L CuSO4 No reaction, novoltage

3 Zn + 1mol/L ZnSO4 Mg + 1mol/L MgSO4 0.25V4 Zn + 1mol/L ZnSO4 Pb+ 1mol/L

Pb(NO3)2

0.5V

5 Mg + 1mol/L MgSO4 Cu + 1mol/L CuSO4 0.7V6 Pb+ 1mol/L

Pb(NO3)2

Cu + 1mol/L CuSO4 0.15V

7 Mg + 1mol/L MgSO4 Pb+ 1mol/LPb(NO3)2

0.45V

Analysis: The greater the difference in reduction potentials the greater the EMF of thecell. Trial 2 did not work as the copper wire was unable to allow the transfer of ions betweenelectrolyte solutions in order to maintain electrical neutrality. Having an imbalance inpositive and negative ions in solution is impossible. All recorded voltages were lower than the theoretical ones due to a number of different

Analysis: The greater the difference in reduction potentials the greater the EMF of thecell. Trial 2 did not work as the copper wire was unable to allow the transfer of ions betweenelectrolyte solutions in order to maintain electrical neutrality. Having an imbalance inpositive and negative ions in solution is impossible. All recorded voltages were lower than the theoretical ones due to a number of differentfactors:

→ Contaminated beakers, making solutions not 1mol/L– use each metal and electrolyte in beaker oncethen replace

→ Experiment not conducted at standard conditions,i.e. not at 25°C – control the temperature with e.g.air conditioner unit

→ Imperfect equipment; resistance from theconducting leads and voltmeter – use new copperconducting leads and a digital voltmeter.

Gather and present information on the structure and chemistry of a dry cell or lead-acidcell and evaluate it in comparison to one of the following:

- button cell- fuel cell- vanadium redox cell- lithium cell- liquid junction photovoltaic device (e.g. the Gratzel cell)

in terms of:- chemistry- cost and practicality- impact on society- environmental impact

Dry Cell Battery (Leclanché cell) Feature CommentVoltage 1.5VAnode (-) Zinc (outer casing)Anode Half Equation Zn(s) → Zn2+(aq) + 2e-

Cathode (+) Carbon (graphite) rod surrounded bysolid MnO2

Cathode Half Reaction 2MnO2(s) + 2H+(aq)+ 2e- → Mn2O3(s) +H2O(l)[The Mn is being reduced from +4 to +3]

Electrolyte NH4Cl (aq) (ammonium chloride paste)Other Information (e.g. Details on howthe battery functions)

The outer Zinc casing is the anode whilst theCarbon (graphite) rod surrounded by solid

Cathode (+) Carbon (graphite) rod surrounded bysolid MnO2

Cathode Half Reaction 2MnO2(s) + 2H+(aq)+ 2e- → Mn2O3(s) +H2O(l)[The Mn is being reduced from +4 to +3]

Electrolyte NH4Cl (aq) (ammonium chloride paste)Other Information (e.g. Details on howthe battery functions)

The outer Zinc casing is the anode whilst theCarbon (graphite) rod surrounded by solidMnO2 acts as the cathode. Zinc atoms areoxidised into ions whilst Manganese ions arereduced from an oxidation state of (+4) to(+3) in an aqueous electrolyte paste ofammonium chloride. MnO2 is mixed withpowdered carbon to increase theconductivity. Reaction occurs once thepositive terminal is connected with thenegative terminal.

Cost and Practicality + Dry cell batteries are cheap to produce+Small in size makes it practical for portabledevices- However it does not produce a very largeamount of electricity for its size.+ It is widely used in portable appliancessuch as calculators, radios, and torcheswhich require only small currents.- It possesses a relatively short shelf-life ofaround 1.5 years- If current is drawn rapidly from the cell, adrop in voltage is caused.- The battery is also prone to leakage as thezinc casing is oxidised during use andthrough reactions with the NH4Cl- Non-rechargeable+ Low cost means they are easily replaced

Effect on Society + Was the first commercialised battery, sohad a massive impact on society; allowingfor electrical goods to be made portable.+ Now used in everyday appliances andis the most prevalent battery in society

Effect on the Environment + Dry cell batteries cause minimalenvironmental problems upon disposal asthe manganese(III) is readily oxidised toinsoluble manganese(IV) oxide, the zinccasing causes no significant problems, andammonium salts and carbon are harmless.(i.e. non-toxic waste products)- Being non-rechargeable means that itcontributes to landfill. The magnitude of itsusage in society means that a very largeamount of these batteries end up in landfill.

Silver Oxide Button cellFeature CommentVoltage 1.6 VAnode (-) ZincAnode Half Equation Zn(s) + 2OH-1(aq) → Zn(OH)2(s) + 2e-

[zinc atoms are being oxidised to zincions]

Cathode (+) Graphite (C) + Silver Oxide (Ag2O) pasteCathode Half Reaction Ag2O(s) +H2O(l) +2e- → 2Ag(s) +2OH-1

(aq)[silver ions are reduced to silver atoms]

Electrolyte Potassium Hydroxide (KOH) pasteOther Information (e.g. Details on Zinc acts as the anode whilst silver oxide acts

Anode Half Equation Zn(s) + 2OH-1(aq) → Zn(OH)2(s) + 2e-

[zinc atoms are being oxidised to zincions]

Cathode (+) Graphite (C) + Silver Oxide (Ag2O) pasteCathode Half Reaction Ag2O(s) +H2O(l) +2e- → 2Ag(s) +2OH-1

(aq)[silver ions are reduced to silver atoms]

Electrolyte Potassium Hydroxide (KOH) pasteOther Information (e.g. Details onhow the battery functions)

Zinc acts as the anode whilst silver oxide actsas the cathode. Zinc atoms are oxidised tozinc ions whilst silver ions are reduced tosilver atoms in a KOH electrolyte. The carbon(graphite) and silver produced assist theconductivity of the cell. Constant OH-1

concentration helps to maintain stable voltage.Cost and Practicality - High cost due to expensive materials (Ag2O)

+ High energy capacity per unit weight+ Long operating life (e.g. will keep a watchrunning non-stop for 3-5 years)+ Long shelf life+ Produces a very steady output of 1.5V+ Widely used in cameras, heart pacemakers,watches, hearing aids- Poor low temperature performance

Effect on Society + Has had a major contribution as a miniaturepower source in providing reliable energyoutput and minimal toxic waste products. Thishas allowed the development of potableminiature devices such as laser pointers,miniature cameras etc. It has also allowed forthe development of medical devices such asheart pacemakers and hearing aids.

Effect on the Environment - Older variations contain trace amounts ofmercury which is a toxic heavy metal.+ Can be recycled due to the value of silver+ Newer variations are mercury free andproduce harmless waste products- KOH is however highly caustic and cancause burns if casing is damaged.

Solve problems and analyse information to calculate the potential requirement ofnamed electrochemical processes using tables of standard potentials and half-equations To deduce what is being oxidised/reduced:

1) List what all possible reactants are (including water)2) Locate all possible reduction reactants (i.e. reactants on the left side of the

reduction table – that is metal ions and non-metal atoms). Now the onefurthest down the table is the one which undergoes reduction (highestreduction potential).

3) Similarly locate all possible oxidation reactants (i.e. reactants on the rightside of the reduction table – that is metal atoms and non-metal ions). Nowthe one closest to the top of the table is the one which undergoesoxidation (highest oxidation potential).

4) Do the equations, calculate the total EMF of the cell, if positive the reactionwill occur, if negative the reaction will occur in the other direction.

reduction table – that is metal ions and non-metal atoms). Now the onefurthest down the table is the one which undergoes reduction (highestreduction potential).

3) Similarly locate all possible oxidation reactants (i.e. reactants on the rightside of the reduction table – that is metal atoms and non-metal ions). Nowthe one closest to the top of the table is the one which undergoesoxidation (highest oxidation potential).

4) Do the equations, calculate the total EMF of the cell, if positive the reactionwill occur, if negative the reaction will occur in the other direction.

EMF(total) = EMF(reduction) + EMF(oxidation)

Some info not associated with a dot pointThe standard hydrogen electrode is the standard in which all reduction potentials aremeasured. It consists of a platinum electrode immersed in a solution containing 1mol/Lhydrogen ions with hydrogen gas bubbled in at 1 atmosphere of pressure. The reductionpotential is by convention zero and is the reference for which all other reductionpotentials are measured by. The redox table has been developed by comparing thestrengths of oxidants and reductants to that of the standard hydrogen electrode. Reduction potentials are measured under standard conditions: solutions containing1mol/L, gases at a pressure of 1 atmosphere, temperature of 25°C. 5. Nuclear chemistry provides a range of materials

• Distinguish between stable and radioactive isotopes and describe theconditions under which a nucleus is unstable

A stable isotope of an element will not emit radiation, whilst a radioactive isotope willemit radiation and decay. The emission of radiation will continue until the nucleusbecomes sable. Elements with atomic numbers greater than 83 are naturally radioactive.The stability of an isotope depends on several factors: Neutron to proton ratio is too high (excess neutrons):When there are too many neutrons compared with protons then a neutron decays toform a proton and a beta particle (an electron) which is emitted from the nucleus. This isbeta negative decay. 10n → 11H + 0–1e

Example: 14

6C → 147N + 0–1e

Stable light elements (Z less than 20) have a n:p ratio of approximately 1.But rememberthe stable n:p ratio increases with atomic number, e.g. at Z=50 the stable ratio is 1.3.There are also exceptions e.g. Cobalt-60 undergoes β decay when we might haveexpected it to undergo positron emission/electron capture. If the n:p ratio lies outside acertain zone of stability it is considered unstable Neutron to proton ratio is too low (excess protons):When there are too many protons compared with neutrons then a proton decays to forma neutron and a positron (same mass as an electron with a positive charge). This is betapositive decay (positron emission/decay). 11H

→ 10n + 01e Example: 38

19K →→ 3818Ar + 01e

Electron Capture has the same effect however in this case an inner-orbital electron iscaptured and reacted with a proton to form a neutron.

11H

→ 10n + 01e Example: 38

19K →→ 3818Ar + 01e

Electron Capture has the same effect however in this case an inner-orbital electron iscaptured and reacted with a proton to form a neutron. 11H

+ 0–1e → 10n Example: 201

80Hg + 0–1e → 20179Au

Too many protons and neutrons (nucleus too heavy):When there are too many nucleons then alpha decay occurs. This involves theemission of an alpha particle 42He from the unstable nucleus. All elements with anatomic number greater than 83 and some lighter nuclides undergo alpha decay.(note: it raises the n:p) Example: 238

92U → 23490Th + 42He

Gamma EmissionGamma rays are a type of electromagnetic radiation. Gamma rays are never emitted ontheir own in radioactive disintegrations, they accompany either alpha or beta emissions.

Alpha particles Beta particles Gamma Rayshelium nuclei (4

2He) electrons (0–1e) electromagnetic radiation

Mass of 4 amu Very small mass(5 x 10-4 amu)

No mass

2+ charge 1- charge No massLeast penetrating type ofradiation, travels though

5cm of air, easily stopped orabsorbed by a thin sheet of

paper or skin

More penetrating, travelsthrough 100cm of air,

stopped by 5mm thick sheetof Al

Most penetrating, can passthrough several cm of lead

or more than 1m of concrete

Deflected by both electricand magnetic fields,

attracted to negative plate

Deflected by both electricand magnetic fields,

attracted to positive plate

Unaffected by electric andmagnetic fields

Moves relatively slowly(5% c)

Moves at almost any speedup to ~ 99% c

Travels at c

• Describe how transuranic elements are produced

Elements beyond uranium (Z=92) are called transuranic elements. They can besynthesised in a number of ways: Neutron bombardment

Neutrons bombard target atoms, Cobalt-59 + 10n ®

Then combine with bigger atomic number, Cobalt - 60 ®(Usually occurs in a nuclear reactor as it is a good source of neutrons.Neutrons are readily absorbed by the nucleus without the need to beaccelerated [no charge]) [note the above example is not transuranic]

Alpha bombardment

Accelerated alpha particles (helium nuclei) bombard target atom,E.g. 27

13Al+ 42He ® 3015P + 10n

Bombardment with Charged Particles

-Transuranic elements with higher atomic numbers (Z>95) are produced by firingaccelerated charged particles (usually nuclei of light elements, e.g. boron, carbon,oxygen) into the target nucleus.

Accelerated alpha particles (helium nuclei) bombard target atom,E.g. 27

13Al+ 42He ® 3015P + 10n

Bombardment with Charged Particles

-Transuranic elements with higher atomic numbers (Z>95) are produced by firingaccelerated charged particles (usually nuclei of light elements, e.g. boron, carbon,oxygen) into the target nucleus.-These particles are accelerated in a particle accelerator (linear accelerators,cyclotrons, synchrotrons)- Done to overcome the electrostatic repulsion between the positively chargedparticle and target nucleus.

E.g. 64

28Ni + 20983Bi ® 272

111Rg + 10n

• Describe how commercial radioisotopes are produced

Commercial radioisotopes are produced using particle accelerators (Z>95) or nuclearreactors (as they are a good source of neutrons). In a nuclear reactor, suitable targetnuclei are placed in the reactor core where they are bombarded by neutrons to producethe required isotope. E.g. Cobalt – 60 is produced by neutron bombardment by placing asample of Cobalt – 59 in a reactor where it captures a neutron. 59

27Co + 10n ® 6027Co

In particle accelerators, positively charged particles (e.g. nuclei of small elements) areaccelerated to very high velocities (in order to overcome the strong electromagneticrepulsion force of positively charged particles to penetrate the target nucleus). The targetnucleus is bombarded with these accelerated particles in order to synthesise a newradioisotope. E.g. 27

13Al+ 42He ® 3015P + 10n

Process information from secondary sources to describe recent discoveries of elements Transuranic elements do not occur naturally, and are all radioactive. Elements Z= 93, 94, 95, all been produced by neutron bombardment of uranium. Any elements Z>95, require high-energy particle accelerators to be produced. 1940’s – First of the transuranic elements made in nuclear reactors1950’s – 1960’s, Transuranic elements up to 105 produced from high speed particles1974 – Element 106 produced1981 – 1984, elements 107, 108, 109 were produced

(Bohrium, Hassium, & Meitnerium)1994 – Elements 110 & 111 were produced1996 – Element 1121999 – Element 114, 116 and 118(memorise 1: e.g. element 112 (Uub) was synthesised in 1996 in the lab by smashingtogether small elements (isotopes of Zn and Pb) at high energies using a heavy particleaccelerator)

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

Photographic film – Darkening of photographic film indicated the presence ofradioactivity. Used today in the form of radiation badges; the amount of darkening of thefilm is a measure of the amount of radiation that the worker has received. Cloud Chamber – Contains a supersaturated vapour of water or alcohol. Radiationionises some of the air molecules around it causing the vapour to condense, producing“cloud tracks”. These tracks are characteristic of the type of radiation ~ alpha particlesform straight, short, thick tracks, beta particles form thinner, longer zig-zag tracks,gamma rays form long faint tracks.

Photographic film – Darkening of photographic film indicated the presence ofradioactivity. Used today in the form of radiation badges; the amount of darkening of thefilm is a measure of the amount of radiation that the worker has received. Cloud Chamber – Contains a supersaturated vapour of water or alcohol. Radiationionises some of the air molecules around it causing the vapour to condense, producing“cloud tracks”. These tracks are characteristic of the type of radiation ~ alpha particlesform straight, short, thick tracks, beta particles form thinner, longer zig-zag tracks,gamma rays form long faint tracks. Geiger-Muller Counter – Again based onthe ionising properties of radiation.Radiation enters through a thin window, hitsa gas molecule (usually argon) and ionisesit by knocking an electron out of it, whichaccelerates due to the strong E fieldcreated by the high voltage applied,causing more gas molecules to ionise. Anelectric pulse is created which is amplifiedand measured to determine radiation exposure. Scintillation Counter – Uses the fact that some substances (e.g. zinc sulfide) producesa flash of light (scintillation) when struck by radiation (excites the electrons to producephotons). This flash of light can be collected and amplified in a photomultiplier tomeasure the amount of radiation.

Use available evidence to analyse benefits and problems associated with the useof radioactive isotopes in identified industries and medicine.

Benefits Problems

• allows treatment and tracingof medical illnesses andproblems (e.g. Technetium– 99m)

• allows development indifferent applications due totheir unique properties suchas…

• allows safer, and longer-lasting foods (e.g. cobalt-60)

• production of materials (withthickness gauges – cobalt -60)

• leak detection tracing (e.g.sodium – 24)

• medical sterilisation (cobalt –60)

• smoke alarms (e.g.Americium – 241)

• requires nuclear reactors:accidents of operation

• Expensive (some)• emissions produced and

disposed radioactive waste• can cause damage to organisms

if not used and stored safely(infection, cancer, tissuedamage)

• α,β and γ radiation can causedisruption to cellularprocesses due to the ionisingability of radiation.Radioactive elements that getincorporated into the bodyare particularly dangerous.

• in medical diagnosis, wasteneeds to be removed quickly,due to chemicals formed

• Identify one use of a named radioisotope:- in industry- in medicine

In industry – Cobalt-60 is used in industry to irradiate food and prolong shelf life bydestroying bacteria. In medicine – Technetium-99m is widely used in medicine for diagnosis such asdetecting brain tumours, blood circulation disorders, and heart damage after a heartattack.

• Identify one use of a named radioisotope:- in industry- in medicine

In industry – Cobalt-60 is used in industry to irradiate food and prolong shelf life bydestroying bacteria. In medicine – Technetium-99m is widely used in medicine for diagnosis such asdetecting brain tumours, blood circulation disorders, and heart damage after a heartattack.

• Describe the way in which the above named industrial and medicalradioisotopes are used and explain their use in terms of their chemicalproperties.

Cobalt-60 in industry – Food irradiation makes use of gamma radiation as it is effectivein destroying certain biological molecules such as bacteria. Benefits associated with using Co-60: By destroying bacteria and moulds, food is made safer and fresher for longer (longershelf life). This would also reduce wastage. The gamma rays emitted by Co-60 provide sufficient energy to destroy bacteria but notenough energy to make the food radioactive. Co-60 also has an appropriately long half life (4-6 years) to minimise replacement butalso short enough to produce a reasonable intensity of radiation. Arguments against

- It does not necessarily kill all dangerous organisms- Some vitamin content is destroyed- May lead to the formation of harmful compounds in the food- Can lead to laxity of hygiene standards by food handlers

Technetium-99m in medicine – Combined with different compounds, such as a tincompound which allows it to become attached to red bloody cells, and used to studydifferent areas of the body. This is made possible as it is a gamma radiation emitterwhich can be detected and traced to indicate abnormalities. Benefits associated with using Tc-99m:

- Due to its short shelf life (6 hours), it rapidly decays and sominimal exposure and damage is caused to the patient

- Can be combined with other substances in order to transportit to the desired location in order to study and diagnosedifferent areas, e.g. the brain, kidneys, bone, liver andspleen

- It emits readily detectable gamma rays (140keV)- Gamma radiation emitted has relatively low energy- Tc-99m can be changed to a number of oxidation states. This

enables production of a wide range of biologically activechemicals.

A minor disadvantage - Due to its short shelf life, it is implausible to be transported directly from a nuclearreactor. It must thus be created on site by the beta decay of Mo – 99 (which has asufficient half life of 67 hours) in packaged Tc-99m generators.- 3 -

sufficient half life of 67 hours) in packaged Tc-99m generators.- 3 -