Hsc Chemistry Module 9.2 Summary 583h5a

HSC Chemistry Module 9.2 Summary 1. Fossil fuels provide both energy and raw materials such as ethylene, for the production of other substances Construct word and balanced formulae equations of chemical reactions as they are encountered Gather and present information from first-hand or secondary sources to write equations to represent all chemical reactions encountered in the HSC course Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum

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Most of the ethylene (C2H4) used in industry is sourced from the cracking of longer hydrocarbon fractions obtained from the fractional distillation of petroleum, where the fractions are separated according to their respective boiling points. Many of the fractions obtained from petroleum refining are not in high commercial demand, and so are cracked into smaller hydrocarbons, such as ethylene, which are in much higher demand. Cracking is the process in which long hydrocarbon chains are essentially broken into smaller chains. For example, the following reaction shows the cracking of pentadecane. Cracking can either be done through thermal cracking or catalytic cracking. Thermal cracking, or steam cracking, involves a mixture of alkanes and steam, which is heated to 700-1000°C at just over one atmospheric pressure, and ed through hot metal coils. As a result, the alkanes are decomposed into small alkenes, including ethylene. In Australia, this process is primarily used today to convert ethane, source from natural gas, into ethylene. Catalytic cracking is a similar process, but carried out at lower temperatures (500°C) at above one atmospheric pressure, in the absence of air, and in a column called a ‘cat cracker’. The catalyst used in the process are called zeolites, which are crystalline compounds containing aluminium, silicon, and oxygen, which are called zeolites (crystalline aluminosilicates). Longer chain alkanes are fed into the cracker, and are cracked into an alkane and alkene, which can be further cracked to obtain the desired products. Specific zeolites can be manufactured to control the products obtained, giving greater control over the process than thermal cracking. Some examples of catalytic cracking are shown below.

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

Ethylene, as an alkene, contains a C=C double bond, which is highly reactive as it has a high electron density. This allows ethylene to react readily and rapidly with other substances, and thus can form a wide variety of useful products. Some of these reactions are listed below: -Hydrogenation => Hydrogen reacts with ethylene with a metal catalyst such as platinum to form ethane -Halogenation => Ethylene reacts with a halogen to form a haloalkane. For example: -Hydrohalogenation => Ethylene reacts with a hydrogen halide to from a haloalkane. For example: -Hydration => Ethylene reacts with water to form ethanol, with an acid as a catalyst

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

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

Polymerisation is a chemical reaction in which many identical small molecules combine to form one large molecule. The small molecules are called monomers, and the large molecule is called a polymer. Ethylene is able to undergo polymerisation due to the high reactivity of its double bond. Ethylene is the monomer of the polymer polyethylene, which is a widely used polymer in society. Ethylene can also be reacted to form other monomers, such as vinyl chloride and styrene. An addition polymer is a polymer that is formed without any loss of any atoms (i.e. the monomers add together to form a polymer, and no other product is produced). Polyethylene is an addition polymer, as the ethylene monomers add

together in the polymerisation process.

Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer

As can be seen from the above reaction, no other products are produced, and thus polyethylene is an addition polymer. Other addition polymers include polyvinylchloride, polystyrene, and Teflon. Polyethylene is an example of a commercially and industrially important polymer. Two types of polyethylene are manufactured from commercial and industrial use: Low Density Polyethylene (LDPE) and High Density Polyethylene (HDPE). The production of LDPE involves the gas phase process, also known as the high pressure method, named as it is conducted at 100-300 MPa times atmospheric, and at 300°C. A molecule called an initiator is also introduced, usually an organic peroxide (an organic molecule containing an O-O bond), such as benzoyl peroxide. The polyethylene produced in this process contains many branches, and hence its name low density polyethylene. The production of LDPE involves three steps: initiation, propagation, and termination. Initiation The organic peroxide molecule splits into two peroxide radicals, which contains an unpaired electron, and is thus highly reactive. The radical then activates an ethylene molecule by reacting with the double bond to form a single bond, and attaching to one end of the ethylene molecule.

Propagation The activated ethylene-radical molecule is also a radical, and so continues to react with other ethylene molecules. This causes a polymer chain to propagate.

In the production of LDPE, the long polymer molecules often curl backwards upon themselves, and remove a hydrogen atom from a CH2 group in the chain. This is called back-biting, and causes the polymer chain to become branched, hence forming a low density polymer. The diagram below shows back-biting occurring in a polyethylene chain.

Termination Eventually two propagating polyethylene chains react in a chain terminating reaction, and thus terminate the polymerisation and from a long chain.

If one chain has x number of monomer units, and the other chain has y number, the polymer chain has x+y number of monomer units. Chain termination occurs randomly, so the length of the polymer chains varies greatly. As a result, polymer chains have an average molecular mass, instead of a discrete mass.

Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process

HDPE is produced in the Ziegler-Natta process, which occurs at only a few times atmospheric and at around 60°C. This process involves an ionic catalyst called the Ziegler-Natta catalyst, usually consisting of titanium chloride and trialkylaluminium compound, such as Al(C2H5)3. The polyethylene produced has less chain branching, and thus is able to pack more tightly together and form crystalline regions, hence the name high density polyethylene. The polymerisation of HDPE is similar to that of LDPE, except that it occurs on the surface of the ionic catalyst. In the process, ethylene molecules are added to the growing molecule on the surface of the catalyst, which significantly reduces chain branching.  Refer to report 9.2.1 k) METHOD  Three ethylene molecules were modelled using a molecular modelling kit, with black balls for carbon and white balls for hydrogen. The double bond in one of the ethylene molecules was broken and added to the second molecule, which was then added to the third molecule, creating a polyethylene chain.

ACCURACY/VALIDITY The model is limited because… o Atoms are not balls, covalent bonds are not sticks o It is a simplified representation of a complex chemical process o The colours are not accurate o Model does not for produced conditions (e.g. temperature, pressure, enthalpy change) of polymerisation  The model is useful however, as it demonstrates polymerisation in a simple and reliable manner Vinyl Chloride Systematic name: chloroethene Formula: C2H3Cl OR CH2=CHCl 

Identify the following as commercially significant monomers:  vinyl chloride  styrene by both their systematic and common names

It is essentially an ethylene molecule with a chlorine atom substituted in place of a hydrogen atom. Polymer formed: Polyvinylchloride (PVC), which is a commercially significant polymer. The diagram below shows a polyvinylchloride chain.

Styrene Systematic name: phenylethene Formula: C8H8 OR CH2=CHC6H5

Styrene is essentially an ethylene molecule with a benzene ring, or a phenyl group, substituted in place of a hydrogen atom. Polymer formed: Polystyrene, which is a commercially significant polymer. The diagram below shows a polystyrene chain.

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

Low Density Polyethylene The polymer chains in LDPE are highly branched, as shown below.

Polyethylene also does not contain side groups that stiffen the chain, or extensive cross-linking. As such, LDPE contains very little crystalline regions, and hence has a low melting and boiling point, is flexible, is transparent, and is not very strong. LDPE is also insoluble in water, and is inert. These properties make LDPE suitable for wrapping materials, disposable shopping bags, flexible toys, milk bottles, and squeeze bottles. High Density Polyethylene The polymer chains in HDPE contain little chain branching, and are thus able to pack tightly together and form crystalline regions with stronger dispersion forces. Hence HDPE has a higher melting and boiling point than LDPE, and is also stronger and harder. HDPE is also similarly insoluble in water and inert. This makes HDPE suitable for kitchen utensils, tougher carry/garbage bags, building products, and ‘wheely’ bins for household waste. HDPE is also used for natural gas pipes, replacing the older steel and copper pipes. Polyvinylchloride PVC in its pure form is not particularly useful, as it is hard and very brittle due to the chain stiffening of the chlorine atom. PVC also decomposes when heated or exposed to UV radiation due to the C-Cl bond. PVC can be made useful however when additives are included, due to its flame-retardant and impervious properties, and its ability to be easily moulded. Additives can be included to produce a rigid PVC, which is lightweight, high strength, relatively unreactive. These properties make

PVC suitable for water pipes, external cladding, guttering, down pipes, electrical conduits, waste water pipes, rigid s, floor tiles, kitchen utensils, and credit cards. PVC can also be made flexible through the use of additives or plasticisers. Flexible PVC is used in electrical insulation, garden hoses, and storage bottles. Polystyrene Polystyrene is a durable, lightweight polymer that is a good insulator and able to keep its shape. Polystyrene also contains the large phenyl group, which stiffens the polymer chain and forms crystalline regions. As such, polystyrene can be produced to be hard, transparent, but brittle plastic. This form of polystyrene is used in CD cases and clear plastic drinking glasses. If hydrocarbon gas is bubbled through polystyrene as it is manufactured, the gas bubbles are trapped, forming a plastic most commonly known as Styrofoam. The gas bubbles cause the polystyrene to be an excellent insulator and a highly spongy material. This form of polystyrene is used in drink cups, bean-bag filler, and packing material. Summary Monomer Polymer Ethyleneethene Low density polyethylene (LDPE)

High density polyethylene (HDPE)

Vinyl chloride chloroethene

Styrene phenylethene

Properties Flexible, clear, non-toxic, relatively strong, inert

Strong, nontoxic, rigid, hard, inert

Polyvinylchloride Flame (PVC), used with retardant, additives flexible, durable, relatively inert Flame retardant, rigid, hard, easily moulded, impervious Polystyrene Durable, strong, transparent, hard Durable,

Uses Plastic bags, plastic bottles, wrapping material Kitchen utensils, rubbish bins, natural gas pipes Garden hoses, electrical wire insulation Pipes, pipe fittings, credit cards, floor tiles CD cases, drinking glasses Packaging

spongy, good insulator, lightweight (when gas bubbled through) Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water

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material, drink cups

Refer to report 9.2.1.j) METHOD In a darkened room, add 1 mL of cyclohexane to two test tubes, and 1mL of cyclohexene to two test tubes. Add three drops of red-brown bromine water to one cyclohexane and one cyclohexene tube each, and shake all test tubes equally. Observe any colour changes. SAFETY Cyclohexane and cyclohexene are moderately toxic (eye and skin irritation) and highly flammable => use small volumes, avoid flame Bromine water is toxic by all routes of exposure => use diluted volumes, place in dark fume cupboard Bromoalkanes => toxic by all routes of exposure => dispose of in organic wastes bottle, handle with gloves RESULTS The cyclohexene and bromine water produced a colourless solution, whilst cyclohexane produced no colour change This is because cyclohexene contains a highly reactive double bond, which can react with the bromine water => cyclohexene is an unsaturated molecule, cyclohexane is saturated

Cyclohexane and bromine water do react if exposed to UV light by a substitution reaction Thus alkenes are MORE REACTIVE than their corresponding alkane RELIABILITY The above observations were checked against others in the class, who obtained similar results VALIDITY Cyclohexane/ene was used because they are more stable than their linear counterparts All other variables were controlled (e.g. UV light, temperature) A control was used (the test tubes with no bromine water) The method tested the aim, as cyclohexene was demonstrated to be more reactive than cyclohexane

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The experiment could have been made more valid if sensors and data loggers were used to provide quantitative analysis

2. Some scientists research the extraction of materials from biomass to reduce our dependence on fossil fuels Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry

Explain what is meant by a condensation polymer

Describe the reaction involved when a condensation polymer is formed

Petrochemicals are chemicals that are obtained from petroleum, which is a fossil fuel. Recall that fossil fuels are a non-renewable resource, which means that they cannot be replaced once used in a reasonable timeframe. The current rate at which society consumes fossil fuels is currently unsustainable, because scientists estimate that oil supplies will run out in the foreseeable future at our current rate of consumption. In addition, scientists argue that petroleum will gradually become more expensive as supplies diminish, meaning that the cost of manufacturing plastics from oil will become prohibitive in the future. The manufacturing of plastics currently only s for 3%-5% of total oil production, with most oil being burnt for energy. Also, only a small percentage of plastic is recycled. Thus if we are going to continue to use materials and compounds presently obtained from the petrochemical industry, we need to find alternative sources for manufacturing to continue in the future. Other sources are currently expensive, but with further research and implementation, the cost of production may reduce, and such sources may become more feasible in the future. Condensation polymers are polymers that release small compounds during the polymerisation process when pairs of monomers react. Whilst this is often water, other compounds such as methanol can be released. These compounds are produced when the functional group from two or more monomers react and . Some examples of condensation polymers include cellulose, starch, protein, silk, and nylon. The polymerisation of a condensation polymer differs from that of an addition polymer. No initiator molecule is required in condensation polymerisation, and no double bond opens up to react. Instead, the functional groups of two monomers react, forming a new bond and a small molecule. For example, the polymerisation of nylon-6 involves the monomer below called 6-aminohexanoic acid: The monomer reacts as a condensation polymer, as it releases water when the amine group (H2N) reacts with the carboxylic acid group (COOH)

Describe the structure of Cellulose is the most abundant polymer on Earth, as it constitutes cellulose and identify it as an around 50% of biomass (organic matter). It is a naturally occurring example of a condensation condensation biopolymer, which is a polymer made mostly by living

polymer found as a major component of biomass

organisms. The monomer of cellulose is β-glucose, shown below.

Note how the hydroxyl group at each end of the molecule are flipped. This differs from α-glucose, where the hydroxyl groups are on the same side of the molecule (α-glucose is the monomer of starch) Cellulose is formed when the C1 and C4 of two β-glucose molecules condense to a disaccharide (two sugar units), forming a glycoside bond between the two molecules, and eliminating a water molecule. The β-glucose monomers flip when they react, so that the CH2OH functional group is on alternate side in a cellulose chain. The polymerisation continues, forming cellulose chains of up to 30004000 β-glucose monomer units.

Identify that cellulose contains the basic carbonchain structures needed to build petrochemicals and discuss its potential as a raw material

to include at least three monomer units when drawing polymers. In order to manufacture petrochemicals, substances containing carbon-chain structures are needed. Whilst short-chain alkenes (e.g. ethylene, propylene) are mostly used, cellulose also contains the required carbon-chain in the 6C β-glucose monomer units. So in addition to cellulose being a raw material for products such as paper and cotton, cellulose could also theoretically be used to obtain petrochemicals. Below is a flow chart depicting the process of obtaining petrochemicals from cellulose:

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

The advantage of using cellulose as a raw material for petrochemicals is that cellulose is a renewable resource, and so we could obtain a theoretically limitless supply of petrochemicals. As oil supplies are predicted to run out in the foreseeable future, developing cellulose as a source of petrochemicals would allow us to continue to use petrochemicals. Additionally, cellulose is widespread across the world, and so sources of petrochemicals would be local, reducing the financial and energy costs of transportation. The disadvantage of cellulose as a raw material is that it is currently too expensive for cellulose to be a practical source of petrochemicals. As the flow chart above shows, the process required is lengthy, and is expensive due to the energy considerations of each of the individual steps. This also raises another issue of using cellulose: the high quantity of energy required in this process would come from oil. Thus more oil would be required to produce ethylene from cellulose than if the oil was simply cracked to ethylene, as well as increased release in greenhouse gases. Scientists however are currently developing more efficient methods of obtaining ethylene from cellulose, and so cellulose does have potential use as a raw material for petrochemicals in the future. Name of biopolymer Biopol™, which is a copolymer of polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV). The systematic name for Biopol is poly-3hydroxybutyrate-poly-3-hydroxyvalerate (PHBV)

Enzyme/organism used in synthesis Ralstonia eutrophus, a bacterium(formerly Alcaligenes eutrophus) Production In industrial production, Ralstonia eutrophus bacteria are grown in a favourable environment (tanks with carbon-based food source, and limited nutrients such as phosphorus and nitrates). When bacteria levels are high enough, the environment is changed so that it is high in glucose and valeric acid, but low in nitrogen. This causes the bacteria to produce the PHBV polymer (Biopol) in their cell walls as granules (small pellets). The extraction of the polymer involves dissolution in hot CHCl3 (trichloromethane), centrifugation to remove solid waste, and then extracting the polymer as a powder, which is then treated further.

Properties  Biodegradable (2 years)  Biocompatible (can exist with other living tissue or organisms without causing harm)  Non-toxic  Insoluble in water  Resistant to UV light, acids and bases  High tensile strength  High melting point These properties are similar to those of polypropylene. Uses in relation to properties  Disposable items, such as razors, rubbish bags, cutlery, nappies, and shampoo bottles => biodegradable, therefore environmentally safe  Surgical applications, such as surgical pins and dissolvable sutures (stiches) => biodegradable, biocompatible, and resistant, so is safe and ideal to use in the body Advantages of use  Biopol is a biodegradable material, so it has a smaller impact on the environment than other polymers such as polyethylene. Its use also reduces rubbish levels in landfills.  It is a biocompatible material which can be dissolved by enzymes in the body. This means that any surgical applications don’t have to be removed from the body  Biopol is a renewable resource Disadvantages  Biopol is currently very expensive to manufacture, and demand at the moment is not high enough to be economically viable. Recent Developments Gene splicing techniques (1980s) have allowed scientists to place the gene from Ralstonia Eutrophus into the E. Coli bacteria, which grow much more quickly than R. Eutrophus, which makes the manufacturing process cheaper and faster. Scientists have recently discovered (1992) that genetically engineered plants such as cress and potatoes can be made to produce biopolymers. Genes can be taken from microorganisms that make PHB naturally, and then inserted into plants, so the production of PHB would be cheaper, though still much more expensive than petrochemical plastics. Judgement Although Biopol currently costs more to produce than products of the petrochemical industry, its biodegradable and biocompatible properties give it advantageous potential uses. Biopol’s environmental impact would be less than non-biodegradable petrochemical plastics, allowing for healthier ecosystems, better waste management, and less waste in landfills. Whilst its current social impact is very minimal due to its lows usage, Biopol has allowed for surgical materials that would be otherwise very difficult to use, and has the potential for widespread future use as a biodegradable plastic with further research.

Information came from Jacaranda Chemistry textbook, and websites from University of Virginia and manufacturers. http://www.wileyvch.de/books/biopoly/pdf_v04/bpol4003_53_68.pdf

3. Other resources, such as ethanol, are readily available from renewable resources such as plants Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used

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

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

The following equation represents the dehydration of ethanol to ethylene:

The catalyst in the dehydration of ethanol is excess concentrated sulfuric acid, though porous ceramic catalysts are used industrially at 350°C. Concentrated sulfuric acid is used as it is an excellent dehydrating agent. The dehydration of ethanol essentially involves removing a water molecule from ethanol to form ethylene. The following equation represents the addition of water to ethylene to produce ethanol:

The catalyst in the addition of water to ethylene is dilute sulfuric acid vapours or phosphorous acid (H3PO4) at 330°C, as the water is not strong enough to attack the electrons in the ethylene double bond.  Refer to report 9.2.3j) METHOD  A molecular model kit was used, with black balls representing carbon, white balls for hydrogen, and red balls for oxygen.  Addition of water to ethylene o An ethylene molecule and a water molecule were modelled. The double bond of the ethylene molecule was broken, and a hydrogen atom from water was removed. The hydroxy group and hydrogen were added to either end of the ethylene molecule to produce ethanol.

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Dehydration of ethanol o An ethanol molecule was modelled, and then the hydroxyl group and one hydrogen atom from the other carbon atom was removed. The double bond in ethylene is then formed, and the hydrogen atom and hydroxyl group are ed to produce water.

ACCURACY/VALIDITY The models are useful to demonstrate the above processes in a simple visual representation, allowing for a greater understanding of the reactions  The models are limited because… o Atoms are not balls, covalent bonds are not sticks o The proportions of size are not accurate o The above processes involve H2SO4 or other substances as catalysts, which are not represented. o The reactions are more complex than the above models, and involve multiple steps Describe and for the Ethanol is a widely used solvent for its ability to dissolve a wide

many uses of ethanol as a solvent for polar and nonpolar substances

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

variety of substances, both polar and non-polar. This is due to the molecular structure of ethanol.

Ethanol consists of a hydroxyl group (-OH) at one end of the molecule, which is polar, and can form dipole-dipole, dipole-ion, and hydrogen bonds. The alkyl group (CH3) at the other end of the molecule is non-polar and hydrophobic, and can share dispersion forces with other non-polar molecules such as hexane, and oils. Thus many non-polar substances that are not soluble in water are soluble in ethanol, which is why ethanol is a widely used solvent. Once a nonpolar substance is dissolved in ethanol, water can be added to prepare a solution that is mostly water, as ethanol is miscible with water. Ethanol is also used as a solvent as it is the least toxic alkanol. In addition, ethanol has a lower boiling point than water (~78.5°C), and thus evaporates more quickly than water, which is suitable for use in cosmetics. Some of the products in which ethanol is used as a solvent include:  Cosmetics (perfume, deodorant, after-shaves)  Varnishes  Food colourings and flavourings (vanilla essence)  Medical preparations (antiseptics)  Cleaning agents  Methylated spirits (95% ethanol, 5% methanol, plus foultasting chemicals) Ethanol is a liquid fuel that easily combusts: Ethanol is easily transportable, and is widely used as a fuel for hikers and campers. Ethanol has been widely advocated as a fuel for automobiles, as ethanol is considered a renewable resource. Ethanol is considered a renewable resource because it can be derived from biomass sources (e.g. corn, straw) through fermentation. These sources are non-fossil fuel sources, and can be replaced within a short-term timeframe, and hence ethanol can be a renewable resource. Currently ethanol is mainly used as a fuel additive, such as E10 (10% ethanol, 90% petrol). Ethanol fuels >90% can also be used, but they require engine modifications for ethanol blends above 24%.

Present information from secondary sources by writing a balanced equation for the fermentation of glucose to ethanol

Describe conditions under which fermentation of sugars is promoted

Summarise the chemistry of the fermentation process

This information was source from Conquering Chemistry textbook and the University of Virginia website. Fermentation is the process in which glucose is decomposed to ethanol and carbon dioxide by the action of enzymes present in microbes (especially yeast) The following are the conditions under which fermentation of sugars is promoted  Glucose-rich substance  Alcohol-tolerant yeast (Saccharomyces ellipsoideus)  pH of 3.7-4.6 (an acidic environment prevents pathogens from growing)  Temperature of 37°C (around blood temperature) => yeast is a living organism, so works best at around this temperature. Above 37°C the yeast dies, and below the yeast works less efficiently  Mashed up grain of fruit mixed with water => food for yeast, such as diammonium phosphate  Anaerobic conditions (absence of oxygen) to prevent oxidation of ethanol to ethanoic acid  Aqueous environment  <15% ethanol concentration, as the yeast is killed above these temperatures The steps of the fermentation process are the following: 1. Yeast and mashed up grain and water. 2. The enzymes in yeast break down the larger carbohydrates (e.g. starch and sucrose from cane sugar waste or molasses) into simple carbohydrates (glucose and fructose).

3. In an oxygen-free environment (see above for the other conditions), the enzymes in yeast break down glucose into ethanol and carbon dioxide.

Process information from secondary sources to summarise the processes

4. The fermentation process stops at around 15% ethanol concentration, as the ethanol starts killing the yeast. Fractional distillation of the mixture can achieve higher ethanol concentrations (up to 96%). The industrial production of ethanol is similar to the production of ethanol for food and drinks, though uses a few more chemicals. In Northern Queensland, the carbohydrate source for the industrial

involved in the industrial production of ethanol from sugar cane

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

Assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of its use

fermentation is sugar cane waste, or molasses, which is high in sucrose. The steps involved are summarised below.  The harvested sugarcane is crushed to create a pulp of cellulose and sucrose  The pulp is heated to 100°C, and dilute sulfuric acid is added. This hydrolyses the cellulose and sucrose molecules into glucose.  The mixture is filtered to remove the solid residues of lignin and unbroken cellulose from the glucose solution.  The glucose is further hydrolysed with stronger acids and filtered again.  Calcium hydroxide is added to slightly neutralise the sulfuric acid, forming an insoluble calcium sulfate salt. The solution is filtered again to remove the calcium sulfate and other remaining solids.  Water is added to reduce the concentration of glucose to around 40%. Acid is then added to achieve the acidic environment required for fermentation (pH 4-5)  The solution is placed in an oxygen-free tank at the right temperature (around 37°C). Suitable yeast cultures are added to start the fermentation process.  The CO2 that evolves in the fermentation process is captured and purified to sell to other industries (e.g. soft drink companies)  After 2 days the mixture reaches around 10-12% ethanol concentration. The mixture is then distilled to achieve higher concentrations of ethanol. The molar heat of combustion of a compound is the quantity of heat energy released per mole of the complete combustion of a fuel under standard laboratory conditions. Molar heat of combustion is measured in kilojoules per mole (kJmol-1) Recall that enthalpy change (ΔH) is assigned negative values for exothermic reactions. Thus molar heat of combustion is the negative of the enthalpy change for a combustion process. The theoretical value for the heat of combustion of ethanol is 1371 kJmol-1. See below for the first-hand value obtained, and the method used. Ethanol has a significant potential for use as a replacement fuel for petroleum, as crude oil production is predicted to peak and decline in the foreseeable future. Ethanol is currently used in fuel blends such as E10, but in Brazil more than 30% of cars run on >25% ethanol blends, and countries such are China and South Africa are investigating greater use of ethanol fuels. The benefits of using ethanol as a fuel include the following:  Ethanol is a renewable resource, and can theoretically be used indefinitely. One of the major drawbacks of petroleum fuels is that they are non-renewable, and so ethanol fuels are more sustainable than petroleum fuels.  Ethanol that is sourced from biomass is theoretically carbonneutral, as the carbon released in the combustion of ethanol is absorbed during the photosynthesis of the biomass source.

Using carbon-neutral fuels limits the increase of greenhouse gases in the atmosphere as no net carbon dioxide is released into the atmosphere, which is desirable.

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Ethanol requires less oxygen to completely combust than octane, as ethanol contains less carbon atoms. This reduces the production of undesirable products such as carbon and carbon monoxide (which is toxic), thus ethanol is a cleaner and more efficient fuel than octane. Spark plugs also don’t have to be replaced as often, as less carbon is deposited.  Ethanol fuels are less likely to lead to photochemical smog, which is of major concern in urban environments.  Ethanol has a lower ignition temperature than octane, thus more readily ignites.  Ethanol can be produced from local biomass production, which can be locally sourced. Conversely petroleum sources often have to be imported. Local sources of fuel reduce transportation costs (both financial and environmental), improve the local employment, and increase the stability of the supply of fuels. The disadvantages of using ethanol as a fuel include the following:  Existing car engines would need costly modifications to run on hydrous ethanol blends. Anhydrous ethanol can be blended with fuel only up to 24% ethanol without requiring engine modifications. Greater engine wear occurs with high ethanol-petrol blends, as ethanol fuels require a higher engine compression ratio.  Large areas of arable land would be require to grow the crops required to produce renewable ethanol fuel, which would lead to greater environmental problems, such as soil erosion and deforestation. In addition, the land used for ethanol production would reduce the land available for food supplies, which is problematic considering the food shortage.  The disposal of the waste liquors of fermentation would also cause environmental problems.  The fermentation process is currently too expensive to operate on the large scale required for fuel use.  Ethanol releases less heat per gram than octane, so ethanol is less energy-efficient than octane. Therefore ethanol has a significant potential as a fuel, but is currently not a viable alternative. With further research into ethanol

Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

Identify the IUPAC nomenclature for straightchained alkanols from C1 to C8

Solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes

production however, ethanol could become a commercially viable fuel in the future, and has the potential to become a more attractive fuel than petroleum fuels. Ethanol fuel is predominately used in fuel blends with petroleum, although hydrous ethanol blends of over 99% are available. In Australia, ethanol is subsidised by the government, and significant quantities of fuel consist of 10% ethanol blends sourced from cane in northern Queensland. The success of ethanol blends in Australia has been limited however, as the public is suspicious of the damage that ethanol can cause to engines. Brazil and the US currently have the highest use of ethanol in fuels, ing for 89% of production worldwide. In the 1970s and 80s, the Brazilian government started subsidising the cost of the fermentation of biomass to ethanol for use in car fuels, but this proved to be prohibitively expensive. Brazil has moved back to ethanol fuels recently, with the government in 2007 legislating that all fuels sold must consist of 25% ethanol. Hydrous ethanol fuels are also widely available in Brazil, with a quarter of cars in Brazil running on hydrous ethanol, which has proven to be an efficient fuel. Ethanol fuels are also widely used in the US, with many states requiring that all fuels consist of at least 10% ethanol. Therefore the introduction of ethanol fuel blends has been quite successful around the world. Ethanol is a cleaner and more efficient fuel than octane, but requires engine modifications for use. The success of Brazil’s and the US’s ethanol programs have been attributed to their vast areas of arable land, and may not be possible in many other areas in the world. Ethanol fuels have become more widespread in the 2000s when petroleum fuel prices started rapidly rising, and currently have a high worldwide consumption. Alkanols are molecules where one of the hydrogen atoms in an alkane has been replaced by a hydroxyl group (-OH). To name an alkanol, follow these steps: 1) Remove the –e at the end of parent alkane, and add –ol 2) Add a number prefix to denote the position of the –OH group, counting from the end that gives the smallest number. EXAMPLE

1) The above compound contains five carbons, and so the parent alkane is pentane. We delete the –e and add –ol, so we get pentanol. 2) We could number the carbon where the –OH group is as either 2 or 4. As 2 is smaller, we count from the right, and so we get 2-pentanol.  Refer to report 9.2.3 m) METHOD  20g of glucose was mixed with 150mL of lukewarm (~37°C) water and 5g of yeast, then poured into a 250mL side-arm conical flask and stoppered. The flask was weighed on an

electronic scale, and then placed into a water bath at ~37°C. The flask was weighed every ten minutes until no mass change was observed.

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For a valid experiment, follow the above procedure for another glucose solution, but DO NOT add yeast => this acts as a control Tests for substances o CO2: Bubble the released gas through limewater (Ca(OH)2 solution) o Ethanol: Ignite a small volume with care, which will produce a colourless flame if ethanol is present the conditions for fermentation => these must all be present in the method SAFETY Ethanol is a flammable substance => do not expose to flame RESULTS Initial mass: 310.3g Final mass: 309.4g (after 40 minutes) Mass change: 0.9g Volume of CO2 released: 0.5L % glucose fermented: 9% Fermentation reaction: The dot point asks to solve problems, which means that you may be asked to calculate volume of CO2 released, or other such problems RELIABILITY The experiment was not repeated, and no average mass loss was obtained The glucose solution was kept at a constant temperature 37°C), which improves the consistency of the investigation VALIDITY The investigation tested the aim by monitoring mass changes during fermentation A control was used Other variables (temperature, pressure) were kept constant Electronic scales were used (accuracy) The water bath ensured optimal fermentation Stoppered beaker allowed not extra mass to enter or leave the beaker apart from CO2 gas

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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

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The time of fermentation was relatively short, which minimised mass loss due to water evaporation => maximised the proportion of CO2 mass loss to total loss Refer to report 9.2.3o) METHOD The heat of combustion of methanol, ethanol, and 1proponol were measured Each of the above alkanols was placed in a spirit burner, and their initial mass was recorded. 200mL of water was poured into a tin can, and the initial temperature was recorded. One spirit burner was placed under the tin can, and then lighted so that the flame touched the bottom of the can. Monitor the temperature of the water, and once it has increased by 10°C, extinguish the flame. The burner was immediately weighted again, and the mass change was recorded. The above procedure was repeated for the other alkanols. The results were then analysed with appropriate calculations to determine the heat of combustion of each alkanol.

Draw a diagram of the set-up if possible SAFETY Methanol is toxic by all routes of exposure (can cause blindness if ingested) => wear eye and skin protection RESULTS MASS LOSSES o Methanol: 1.22g o Ethanol: 0.66g o 1-proponol: 0.62g HEATS OF COMBUSTION o Methanol: 220kJmol-1 o Ethanol: 584kJmol-1

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o 1-proponol: 1147kJmol-1 THEORETICAL HEATS OF COMBUSTION o Methanol: 726kJmol-1 o Ethanol: 1360kJmol-1 o 1-proponol: 2020kJmol-1 Methanol had the lowest heat of combustion, 1-proponol had the highest heat of combustion o This is because more bonds are created in the formation of the products (CO2, H2O) of 1-proponol than methanol ( creating bonds releases energy, breaking bonds absorbs energy) The combustion equations are:

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The heat of combustion calculations required the specific heat capacity equation

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This gave the change in enthalpy, which was then divided by mass of alkanol and moles of alkanol to give both heat of combustion per gram, and molar heat of combustion heat of combustion is POSTIVE, whilst change in enthalpy is NEGATIVE (by convention) RELIABILITY The experiment was not repeated and no average value was obtained VALIDITY/ACCURACY The investigation tested the aim by comparing the heats of combustion The burner was measured with an electronic scale (accuracy) The temperature could have been measured with a thermal sensor and data logger (improving accuracy) A tin can is a better thermal conductor than a glass beaker There was not 100% efficiency in heat transfer between flame and can however => a draught shield around the burner could reduce this Soot under the tin can for 1-proponol indicated incomplete combustion, reducing the heat emitted Heat was lost from the water to the surroundings due to radiation and evaporation => a lid on the can would improve validity All of the above problems contributed to a lower measured molar heat of combustion than the theoretical value

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4. Oxidationreduction reactions are increasingly important as a source of energy Explain the displacement of metals from solution in of transfer of electrons

Displacement reactions are a form of oxidation-reduction reactions, or redox reactions, in which a chemical species is displaced from a solution into another physical state. For metal displacement, this involves a metal ion in solution being displaced into the solid state by the presence of another metal, causing a solid deposit of that metal. As it is a redox reaction, metal displacement involves a transfer of electrons between chemical species. Thus the metal ion is displaced into the solid state because it has gained elec trons from the other metal, and therefore is no longer an ion. For example, when a piece of zinc metal is placed into a solution of copper (II) sulfate, the originally blue solution decolourises, and a reddish-brown metal is deposited on the zinc. This is because the copper ions have gained electrons, or have been reduced, by the presence of the zinc metal, in the following reaction: This reaction can be divided into half equations. Oxidation half equation: Reduction half equation:

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

As can be seen in the above reaction, the zinc metal transferred electrons to the copper ions, which caused them to displace out of solution into a solid deposit. The zinc acted as a reductant by reducing the copper ions, whilst the copper ions acted as an oxidant by oxidising the zinc. A more active metal will displace a less active metal ion from solution. This is because a more active metal is oxidised more easily than a less active metal, so it transfers its electrons to the metal ions in solution. The relative activity of a metal can be determined by using the table of standard potentials, where the metals are listed in decreasing activity. For example, if magnesium metal is placed in a solution containing zinc ions, the zinc ions will be displaced because magnesium is a more active metal than zinc. On the other hand, if zinc metal is placed in a solution containing magnesium ions, no displacement reaction would occur. This is because magnesium is more active than zinc, so zinc is unable to reduce the magnesium ions.

for changes in the oxidation state of species in of their loss or gain of electrons

The oxidation state of a species is the average charge on an ion for each element. In simple chemicals, this is equal to the ionic charge associated with the ions in question, including the charge. For example, the oxidation state for copper in Cu2O (which can be written as 2Cu+O2-) is +1, and the oxidation state of oxygen is -2. When the oxidation state of an element is increased, it has lost electrons, or has been oxidised. For example, the following reaction is the oxidation of magnesium to the magnesium ion. The oxidation state of magnesium is 0. This has been increased to +2, and as can be seen this has corresponded to loss in electrons. When the oxidation state decreases, the element has gained electrons, or has been reduced. For example, the following reaction is the reduction of the iron (II) ion to iron.

Describe and explain galvanic cells in of oxidation/reduction

The oxidation state of the iron (II) ion is 2+. This has been decreased to 0, and in the process it has gained two electrons. There are several rules associated with oxidation states: 1. The oxidation state is equal to the charge on the ion, both positive and negative (e.g. Cu in Cu2O has a state of +1, O has a state of -2) 2. The oxidation state of an element in its stable elemental state is always zero (e.g. Cl2, Ar, S8 all have oxidation states of zero) 3. The sum of all the oxidation states in a polyatomic ion is equal to the charge on the ion (e.g. in MnO4-, the oxidation states of Mn and O add to -1) Compounds containing elements in a high oxidation state tend to be strong oxidants. For example, Cr2O72-, where Cr has an oxidation state of +6, is a strong oxidant. Similarly, compounds with elements with a low oxidation state tend to be strong reductants. For example, active metals such as K have an oxidation state of zero, and are strong reductants. A way of ing the processes of oxidation and reduction is with the acronym OILRIG – Oxidation Is LossReduction Is Gain. Redox reactions involve the processes of oxidation and reduction occurring at the same time. Thus in a redox reaction, there is a transfer of electrons occurring in the system.

reactions

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

A galvanic cell uses this transfer of electrons in order to produce energy through electricity. This occurs because the oxidation and reduction reactions are physically separated, with each process occurring in separate half-cells. The half cells are connected by a conducting wire, in which the electrons are transferred. In the oxidation half-cell, there is a loss of electrons. These electrons flow to the reduction half-cell, as the reduction reaction requires electrons to occur. A galvanic cell also consists of a salt bridge, in which ions are transferred between the two half-cells in order to maintain charge neutrality. This occurs in electricity being produced in the conducting wire, which can be used a source of energy for electrical devices. The following diagram shows a simple galvanic cell consisting of a zinc anode and copper cathode:

The galvanic cell above consists two half cells, one with a copper cathode and the other with a zinc anode. These two electrodes are connected by a conducting wire, and the two half-cells are also connected by a salt bridge, which contains a material such as filter paper soaked in a solution containing an electrolyte, in this case Na2SO4. Each half cell also contains an electrolytic solution, with the copper cathode placed in CuSO4 solution, and the zinc anode in ZnSO4 solution. As can be seen from the table of standard potentials, zinc is a more active metal than copper. Therefore the zinc electrons of the zinc atoms have more energy than the electrons of copper atoms, i.e. the zinc atoms are more easily oxidised to form zinc cations in solution. As electrons flow from higher potential energy to lower potential energy, the electrons flow from the zinc anode to the copper cathode. Simultaneously, the copper ions in the cathode half-cell are being reduced to form copper atoms, so the flowing electrons are absorbed in this process. Thus the flow of electrons is from the anode where oxidation is occurring, to the cathode where reduction is occurring. The salt bridge in the galvanic cell allows the migration of ions between

the two cells. This is necessary because without the salt bridge, the galvanic cell would not produce electricity. The oxidation of zinc produces zinc cations, which increases the charge of the anode half-cell. Similarly, the reduction of copper cations results in a decrease in charge of the cathode half-cell. As an imbalance of charge would result in each beaker without the migration of ions, the redox reaction would not occur without the salt bridge. The salt bridge in the galvanic cell above consists of a material soaked in Na2SO4, although it could contain any electrolyte that would not react with either solution, such KNO3. A solution of KOH would not be suitable however, as the OH- ions would precipitate with the Zn2+ ions, and charge neutrality would not be achieved. The salt bridge allows the flow of ions in order to maintain the charge neutrality of each half-cell. As cations are being produced in the oxidation half-cell, the anions would flow towards the oxidation halfcell. Similarly, as cations are being consumed in the reduction half-cell, cations would flow towards the reduction half-cell in order to maintain the charge of the cell.

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

Anode: The electrode at which oxidation occurs. The anode has a negative sign in galvanic cells, as it is the place in the circuit where electrons leave. A way of ing the definition of an anode is Anode Oxidation =>AN OX Cathode: The electrode at which oxidation occurs. The cathode has a positive sign in galvanic cells, as it is the place in the circuit where electrons move towards. A way of the definition of a cathode is Reduction Cathode =>REDCAT Features of anodes and cathodes Anode Cathode Location of oxidation Location of reduction Has a negative charge Has a positive charge Electrons produced Electrons absorbed Cations move towards Anions move towards Electrode: A component of an electrical circuit through which current es between the metallic and non-metallic parts of the circuit. Nonmetallic parts can include and electrolytic solution, a semi-conductor, gas, or a vacuum. Electrolyte: A substance that conducts electricity due to the movement of ions. This is typically ionic compounds dissolved in water, but can

Gather and present information on the structure and chemistry of a dry cell or lead-acid cell 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 of:  chemistry  cost and practicality  impact on society  environmental impact

include other substances in other states as well. Electricity is conducted due to the movement of ions towards oppositely charged electrodes in the presence of applied voltage, which results in the movement of charge through a medium. Lead-acid battery The lead-acid battery is a battery found often in motor cars. The battery consists of multiple cells, most commonly six. Each produces theoretically 2V, so the battery produces in total 12V. Each cell consists of a sheet of lead (Pb) acting as the anode, and lead dioxide (PbO2) powdered on a lead sheet acting as the cathode. Each cell also contains 35% (w/w), or 4.5M sulfuric acid, which acts as the electrolyte. The lead anode and lead dioxide cathode are connected to an external circuit, and supply a voltage to it as a result of the redox reaction in the cell.

The oxidation reaction at the lead anode is The reduction reaction at the lead dioxide cathode is Both reactions produce an insoluble PbSO4 coating on the respective electrodes, and both cause the concentration of the H2SO4 electrolytic solution to decrease. The degree of charge of the battery can be measured by using a hydrometer, which measures the concentration of H+ in the electrolytic solution.

The battery can be recharged by applying an external voltage that is

greater than 2V per cell. In motor cars, the external voltage comes from the motor-driven generator, or alternator. The external voltage causes both of the above reactions to reverse, thereby increasing the concentration of the H2SO4 electrolytic solution, and removing the PbSO4 coating on the electrodes. Evaluation Cost and practicality The lead-acid battery is relatively cheap to produce, and has a long lifetime as it can recharged. The condition of the battery is also easy to monitor through the use of a hydrometer, and the cell is easy to replace. The cell is also capable of supplying high currents for short periods of time, making it practical for use in starting the engine in motor vehicles. The lead-acid battery does have some drawbacks however. The battery itself is heavy, which limits its practical use to heavy machinery, such as cars and trucks. The cell is susceptible to internal short circuits, which compromises the lifetime of the battery. In addition, the PbSO4 coating tends to disintegrate off the electrodes, and the lead anode slowly corrodes over time, both of which limit the lifetime of the cell. Nevertheless, the lead-acid battery is largely practical in its use as a power source in motor vehicles. Impact on society The lead-acid battery has been in widespread use during the second half of the 20th century, due to its relatively cheap cost of production and its ability to recharge. Its use is significant to the development of motor vehicles, as it is able to provide short bursts of high current to start the engine. This has allowed for efficient transport of freight and people through its use in motor vehicles. The lead-acid battery is also used as a storage battery in remote locations, as it can be charged by a solar power source or an electric generator. This has allowed it to be used as a backup power system for emergency lighting, and a power source for remote locations. Therefore, the lead-acid battery has had a significant impact on society, through its large multitude of uses. Environmental impact The lead-acid battery contains many toxic substances which can harm the environment. The sulfuric acid in the battery can cause significant pollution if spilled, such as in waterways where acids can kill marine life. The lead in the electrodes and antimony in the casing is also toxic to the environment, as both elements are toxic to most forms of life. There are environmental precautions with the lead-acid battery, as the battery casing is strongly sealed, and the lead electrodes can be recycled. This is not always the case however, as lead and acid refuse can be exposed to the environment through damage to the battery, and through improper disposal. Thus the lead-acid battery has a largely detrimental impact on the environment, though there are environmental precautions commonly practised to minimise harm. Vanadium redox cell The vanadium redox cell is a redox flow battery system that is still under development. The cell contains vanadium ions in different oxidation states, andtheir subsequent oxidation and reduction provides electrical power. The quantities of electrical energy it can store are significant,

being measured in megajoules rather than kilojoules for most other storage batteries. The oxidation reaction involves the vanadium species oxidising from an oxidation state of 2 to 3. The reduction reaction involves the vanadium species reducing from an oxidation state of 5 to 4. This can also be thought of as the oxidation state of vanadium reducing from 5 to 4 due to a gain of electrons. The following diagram shows a simplified structural representation of the vanadium redox cell.

The electrodes are made of a graphite felt that is able to conduct electricity. The porous membrane separates two electrolytic solutions that are used in the oxidation and reduction of vanadium species. The electrolyte for the anode, or the anolyte, is a solution VSO4, where V2+ oxidises to V3+. The electrolyte for the cathode, or the catholyte, is (VO2)2SO4. The sulfate ions migrate through the porous membrane in order to maintain the electrical neutrality of both electrolytic solutions. The cell produces electricity through the flow of reactant solutions. Electricity ceases to be produced when the concentrations of V2+ or VO2+ drop significantly through the redox reaction. The cell can be recharged by applying an external voltage to the cell to reverse the flow of electrons. The above oxidation and reduction reactions reverse, restoring the levels of V2+ and VO2+, which allows for future electrical discharge. The cell can also be recharged by replacing spent vanadium fuel with fresh solutions of V2+ and VO2+. This can be done because there are no physical or chemical changes to the electrodes during operation. Evaluation Cost and practicality The vanadium redox cell is currently in the developmental stage. It is a large complicated cell, which means it is not easily portable. Whilst vanadium is a plentiful and cheap chemical, the cell itself is expensive to produce, due to its complicated structure and components. The vanadium redox cell does have significant practicalities however. It can

be theoretically recharged indefinitely, and recharging can be done with a voltage as little as 2V, whilst producing voltages up to 100V on discharge. The system is safe as it produces very little hydrogen gas, which can explode, and there is less risk of the electrolytic solutions releasing sudden charges by mixing. Therefore, whilst the cell is currently expensive as it is still being developed, it has the potential for significant future practicalities. Impact on society The vanadium redox cell is a relatively new development, as it was invented in 1985, and first commercially developed in 1998. Thus its impact on society currently has been insignificant, as it is in very little commercial use. The cell, however, does have potential future uses if used on a widespread commercial scale. The cell could be used as electrochemical storage of solar or wind energy, or as a backup emergency battery system. The cell could also have the potential to be used in electric cars if the cell can be made to be portable. So whilst the impact on society up until now has been minimal, it has the potential to have a significant impact in the future due to the wide possibility of its applications. Environmental impact The vanadium redox cell produces minimal waste, as the components of the cell are recyclable. In addition, the cell can theoretically be recharged indefinitely, which means the wastes associated with the fuels are significantly minimised. Thus the vanadium redox cell’s environmental impact is very minimal due to the recyclable nature of its components and fuels. Comparison of the cells Lead-acid cell Chemistry at lead anode

Cost and practicality

Impact on society

Environmental impact

Vanadium redox cell

at lead/lead dioxide cathode Electrolyte: H2SO4  Cheap to produce  Long life  Can supply high current in short periods  Heavy  Lead anode can corrode  Lead sulfate can disintegrate  Widespread use in motor vehicles  Stores electrical energy from solar/wind power sources  Backup electrical source for emergency lighting  Lead is toxic to living organisms  Sulfuric acid can pollute waterways  Recycling and sealing required

Chemistry at graphite felt anode

Solve problems and analyseinformation to calculate the potential E⦵ requirement of named electrochemical processes using tables of standard potentials and half-equations

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

at graphite felt cathode Anolyte: VSO4 Catholyte: (VO2)2SO4 Cost and  Vanadium is plentiful and cheap practicality  Easily rechargeable  Stores and provides significant quantities of electrical energy  Energy efficient  Expensive to produce  Not portable due to complicated and large structure Impact on  Still in developmental stage society  Little impact on society at the moment due to limited current uses  Potential to store electricity form solar/wind power sources  Potential for use in electric cars Environmental  Minimal waste produced through recycling impact and efficient recharge of fuel  Vanadium safe to use To calculate the potential energy of a galvanic cell, add the two voltages of the relevant oxidation and reduction half-equations. to REVERSE the sign for oxidation half-equations given in the standard table of reduction potentials, as oxidation is the reverse process to the one listed. EXAMPLE For the [Zn | Zn2+ || Cu2+ | Cu] galvanic cell, the relevant standard reduction potentials are

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Zn2+ + 2e¯

Zn (-0.76V)

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Cu2+ + 2e¯

Cu (0.34V)

We need to reverse the sign of the zinc reduction potential, as zinc is being oxidised in the cell. V(total) = 0.76V + 0.34V = 1.10V  Refer to report 9.2.4g)h)  A Daniell cell (zinc and copper electrodes) was set-up according to the diagram below

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The electrolytic solutions were 50mL 1M ZnSO4 and 50mL 1M CuSO4. The filter paper was soaked in KNO3, which was the salt bridge. A multimeter was used to measure the voltage. 50mL of each electrolytic solution was added to each beaker respectively, and the voltage was recorded. RESULTS Voltage at 50mL: 0.40V Voltage at 100mL: 0.40V Therefore the voltage of a galvanic cell does not depend on the quantity or concentration of the electrolytic solutions. By measuring current as well, it can be seen to decrease with time, as the concentration of Cu2+ ions decreases. The half-cell reactions are as follows: Anode: Cathode:

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Perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals an electrolyte solution

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VALIDITY/ACCURACY A potassium nitrate salt bridge was used as neither potassium or nitrate ions react with zinc, copper, or sulfate ions The result is less than the theoretical result because the electrodes may not have been pure, and the experiment wasn’t conducted at standard laboratory conditions. Reliability => repeat results, take an average Refer to report 9.2.4g)h) METHOD The same cell was set up as before, except that zinc, magnesium, aluminium, and iron electrodes/electrolytes (50mL 1M) were tested against copper. The two half cells were connected by the external circuit and the potassium nitrate salt bridge. The voltages of each of these cells were measured using a multimeter and compared. RESULTS Zn|Zn2+||Cu2+|Cu: 0.40V Mg|Mg2+||Cu2+|Cu: 0.95V Al|Al3+||Cu2+|Cu: 0.20V

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Fe|Fe2+||Cu2+|Cu: 0.50V The cathode reaction is…

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The anode reactions are the respective oxidisation reactions of each tested metal. Therefore the order of reactivity of the metals is: Mg, Fe, Zn, Al o This differs from the theoretical order of Mg, Al, Zn, Fe VALIDITY/RELIABLITY/ACCURACY Each cell was tested under the same conditions (temperature, pressure) The order of reactivity did not match the theoretical order, indicating errors in the experiment The voltages obtained were below the theoretical voltages These errors may be due to impurities on the electrodes, the experiment not being carried out at standard laboratory conditions etc.

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

Recall that isotopes are atoms with the same number of protons but different number of neutrons. Isotopes are named by their mass number, such as carbon-14. Below is the standard form for writing isotopes in a nuclear reaction.

M is the element symbol, A is the mass number of the element, and Z is the atomic number. A radioactive isotope is an unstable isotope that will emit radiation to become a stable isotope. The three kinds of radiation that are dealt with in the HSC course are shown below. Radiation Emission α-decay => helium nucleus β-decay => electron γ-decay Gamma radiation A nucleus becomes unstable if it does not have a stable ratio of protons to neutrons, or if the nucleus is too large. The p:n ratio for small nuclei is around 1:1, but for larger elements (Z=80) it tends to 1:1.5. In addition, nuclei with a proton number greater than 83 (bismuth) are also unstable.

For example, uranium-238 undergoes alpha emission. Describe how transuranic elements are produced

Transuranic elements are elements with an atomic number greater than 92 (uranium, which has the highest proton number of the naturally occurring elements). Transuranic elements are produced either by neutron bombardment or nuclei bombardment.

Neutron bombardment involves hitting a non-fissile element (does not undergo fission) with a neutron at high speed in a nuclear reactor, which then forms a new element. This sometimes forms highly unstable nuclei, which then decay into more stable transuranic elements. For example, americium-241 is produced by neutron bombardment of plutonium-239. Neutron bombardment was the first technique discovered for creating new elements, and is typically used to manufacture the first couple transuranic elements. Nuclei bombardment involves bombarding a heavy nucleus with high-speed positive particles, such as helium or carbon nuclei. For example, californium-246 is produced by bombarding uranium-238 with a carbon-12 nucleus.

Describe how commercial radioisotopes are produced

The positive particles need to be at high speed to overcome the electrostatic repulsion forces between nuclei. The particles are accelerated in either linear particle accelerators or cyclotrons. A linear accelerator accelerates particles in a straight line in a cylinder made alternatively positive and negative. Linear accelerators are preferred for high-energy electrons in radiation therapy and research, but can be 1km in length. A cyclotron accelerates particles similarly to a linear accelerator, but in a spiral path, which is achieved by the presence of a strong magnetic field. Cyclotrons take up a lot less space than a linear accelerator, and are used in hospitals to produce medical isotopes. Commercial isotopes are isotopes that are regularly produced for use in industry, medicine, or research. Commercial isotopes are either produced in a nuclear reactor, or in a cyclotron. Isotopes that are manufactured by neutron bombardment are produced in a nuclear reactor. In Australia, such isotopes are produced at ANSTO’s Lucas Heights HIFAR (High Flux Australian Reactor). Nuclear reactors produce neutron-rich isotopes for commercial use. Technetium-99m, a widely use isotope in medicine, is produced at facilities such as Lucas Heights by neutron bombardment of the molybdenum-98 to produce molybdenum-99, which then betadecays to tehcnecium-99m.

Other commercial isotopes produced at the ANSTO facility include chromium-51, copper-54, and iodine-131. Other commercial isotopes are produced in cyclotrons, such as the National Medical Cyclotron at RPA hospital. Cyclotrons produce neutron-deficient isotopes for commercial use. Cyclotrons differ from linear accelerators by having a strong magnetic field to cause the positive particles to follow a spiral path, and thus take up much less space. Cyclotrons produce commercial isotopes such as iodine-

Process information from secondary sources to describe recent discoveries of elements

Identify instruments and processes that can be used to detect radiation

123, carbon-11, and fluorine-18. The advancement in nuclear technology has led to transuranic elements being gradually discovered since the 1940s. There have been four elements that have been discovered in the 21st century. Ununhexium (element 116) Element 116 was discovered in December, 2000 by the t Institute for Nuclear Research (Russia). It was formed by the fusion of curium248 and calcium-48, and decays within 48 milliseconds. Ununpentium (element 115) Element 115 was discovered in February, 2004 by the t Institute for Nuclear Research (Russia) and the Lawrence Livermore National Laboratory (USA). It was formed by the fusion of americium-243 and calcium-48. Ununtrium (element 113) Element 113 was discovered in February, 2004, and was formed by the alpha decay of element 115. Ununoctrium (element 118) Element 118 was first synthesised in October 2006 by the Lawrence Livermore National Laboratory (USA). It was formed by the fusion of californium-249 and calcium-48, but only three atoms of element 118 have been confirmed to have been produced. Information came from textbooks and the IUPAC website: http://www.iupac.org/publications/pac/1997/pdf/6901x0179.pdf Photographic film Photographic film darkens in the presence of radiation, and this was the way that radiation was first detected. Scientists working in areas of potential radiation exposure wear badges made of photographic film to detect radiation. Geiger- Müller counter A Geiger counter consists of a metal tube filled with argon gas with a high potential difference between the opposite sides of the tube. When radiation enters the tube, it ionises the argon by knocking off one of its electrons. The electron then accelerates towards the positively-charged central electrode, and causes more gas particles to ionise in the process. This causes an electric pulse, which is amplified then detected by either audio clicks or a digital reader to measure the intensity of the radiation.

Scintillation counter A scintillation counter consists of substances such as zinc sulfide that emit photons (i.e. flashes of light) in the presence of high-energy radiation. A photo-receptor detects these flashes, and calculates the intensity of radiation. Different substances are used for each type of radiation, and so the type of radiation is also detected.

Identify one use of a named isotope:  in industry  in medicine Describe the way in which the above named industrial and medical radioisotopes are used and explain their use in of their properties

Industry: Caesium-137 (Cs-137) is used as a thickness gauge Medicine: Technetium-99m (Tc-99m) is used to diagnose circulatory problems, such as blood clots. Industry: Caesium-137 PROPERTIES OF Cs-137  It is a low-energy gamma and beta radiation emitter.

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It has a half-life of 30 years

USE Cs-137 is used as a gauge to detect the thickness of manufactured goods, such as steel sheets, paper, and aluminium foil. Cs-137 is placed in a fixed position, and the gamma radiation is directed towards the material, with a detector fixed on the other side. As the intensity of gamma radiation decreases as it es through a material, the detector measures the intensity of gamma radiation in order to determine the thickness of the material ing through.

USE IN OF PROPERTIES  The long half-life of Cs-137 (30 years) means that the source lasts for a long time without replacement, which reduces costs.  The low-energy emission means that safety precautions are minimal, and so that the material absorbs a significant proportion of the gamma radiation, and can thus be detected. Medicine: Technetium-99m PROPERTIES OF Tc-99m  It is a low-energy gamma radiation emitter  

It has a half-life of 6 hours It is reasonably reactive

USE Tc-99m is incorporated into some blood serum and then injected into a patient’s bloodstream. The distribution of Tc-99m throughout the bloodstream is then measured with a scintillation counter, which

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

allows doctors to detect and diagnose blood clots, constrictions and other circulatory problems. Tc-99m can also be used to detect brain tumours. USE IN OF PROPERTIES  Tc-99m emits low-energy gamma radiation, so it causes minimal tissue damage, whilst can still be detected.  It has a short half-life of 6 hours, so the radiation is quickly eliminated from the body  Tc-99m is reasonably reactive, and so can form compounds with particular properties to concentrate in an organ of interest, such as the heart of liver Benefits INDUSTRY  Radioisotopes have allowed for more sensitive, precise, and reliable monitoring equipment, such as thickness gauges.  They have allowed for the detection of leaks, structural faults and weld faults in buildings and materials that otherwise would have been impossible without permanent damage.  The sterilisation of medical supplies is now more reliable and efficient with the use of radioisotopes. MEDICINE  Radioisotopes have created a wide range of non-invasive diagnostic procedures that would otherwise have been impossible  They have allowed the introduction of radiotherapy for the treatment of cancers Problems INDUSTRY AND MEDICINE The problems with the use of radioisotopes are similar for both industry and medicine. The two main problems are health risks and storage issues. Health risks Alpha, beta and gamma radiation can all cause various undesirable reactions in living tissue, which can lead to health complications. Ionising radiation (particularly α) can may disrupt cellular reactions, and may lead to tissue damage, cancer, or genetic damage. For example, Strontium-90 relaces calcium in bones, leading to leukaemia. Therefore safety measures must be adhered to minimise exposure to radiation, such as radiation badges. Storage As the radiation from radioisotopes can potentially cause health risks, they must be stored in a shielded container to prevent radiation leaks. This is sometimes logistically difficult, and adds to the cost of using radioisotopes. In addition, any nuclear waste with a long half-life must be stored in an isolated area, and sealed in thick concrete to minimise radiation exposure to the environment. This is a significant cost associated with the use of radioisotopes.