HSC Chemistry Notes. Construct words and balanced formulae equations of chemical reactions as they are encountered.

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1 Production of Materials HSC Chemistry Notes Construct words and balanced formulae equations of chemical reactions as they are encountered. Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum. Petroleum (crude oil) is a complex mixture of hydrocarbons consisting mainly of alkanes and smaller quantities of other hydrocarbons such as alkenes. Crude oil is separated by fractional distillation into fractions, producing a large fraction of low-worth alkanes with 15 or more carbon atoms. These large molecules (high molecular weight= high BP) are broken into smaller molecules (low molecular weight= lower BP) by cracking, which can be done by heating (Thermal cracking) or by the use of a Zeolite catalyst (Cat Cracking) in the absence of oxygen - covalent bonds are broken. In catalytic process heavy crude oil vapour is combined with a hot catalyst (powdered zeolite)- catalyst is powdered to increase SA in order to increase reaction rate. Zeolite is steam cleaned and reused. Cracking is an endothermic reaction that favours high temperatures. Catalyst allows reaction to occur at much lower temp (500 C). Cracked products include ethene, other alkenes and unbranched alkanes (C8H18). Alkenes are produced because there are no atoms to occupy the bond positions that are created. Once cracked the mixture is fed back into the fractional distillation process. Many of the smaller molecules end up in the valuable petrol or diesel fractions. Any ethylene formed is recovered from the gas fraction because it is of high demand. Fractional distillation cracking fractional distillation Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products. Ethylene has a highly reactive double bond which readily splits open leaving a single C-C bond, and creating 2 new bond positions for other atoms/groups to attach to the molecule. The main advantage of the double bond is that ethylene can undergo polymerisation. Alkenes (i.e. ethylene, propene) are the RAW materials for many plastics such as polyethylene and polypropylene. Identify that ethylene serves as a monomer for which polymers are made. Polymerisation: chemical reaction in which many identical small molecules (monomer) combine to form one very large molecule (polymer). Because of its reactive double bond, ethylene is able to undergo polymerisation; ethylene, a monomer, forms the polymer poly (ethylene). Ethylene is used as a starting point in the production of synthetic organic compounds including insecticides, refrigerants, explosives and pharmaceuticals. Other polymers include: starch and cellulose which are made of many glucose molecules; proteins are polymers of amino acids; and DNA is a polymer of nucleotides, sugar and phosphate. Identify polyethylene as an addition polymer and explain the meaning of this term. Addition polymerisation: no additional molecules are produced there is no loss or gain of atoms, the double bond opens which joins monomers to make a polymer. Polyethylene is an addition polymer as the ethylene molecules combine which each other like

2 Addition reactions: a type of reaction ethylene can undergo. One bond in the double bond is broken and the 2 atoms in a diatomic molecule are added on. There are many types of addition reactions: o Hydrogenation: Hydrogen is reacted with ethylene. The product is ethane. o Hydration: Ethylene is reacted with water, using phosphoric acid as a catalyst, to produce ethanol. o Halogenation: Reactive molecules from the halogen group (Fl 2, Cl 2 & Br 2) can all react with ethylene. o Hydro halogenation: A hydro halogen (HCl or HFl) an ethylene react to form halo-ethane. Outline steps in polyethylene production as an example of commercially & industrially important polymer. Form Low density polyethylene (LDPE) High density polyethylene (HDPE) Name of process - Ziegler-Natta process Requirements Polymerisation process Branching of polymer formed Crystalline Recycling symbol High pressure ( x atmospheric), high temp, (300 C), and an initiator (usually an organic peroxide) An initiator is used Significant chain branching, meaning that polymer chains cannot pack closely together or in an orderly way (contain crosslinks between polymer chains) Less crystalline because chains are far apart and light becomes defracted. More transparent Pressure only a few times atmospheric, temperatures of about 60 C, and a catalyst (alumina silicate catalyst). The polymerisation occurs on the surface of the catalyst Unbranched polyethylene molecules that are able to pack closely together in an orderly fashion (no cross-links between polymer chains). No branching so chains are lined up in an orderly fashion. Light can pass through, therefore more crystalline. Less transparent LDPE (soft plastic): Due to its side branching, the chains are further apart weak dispersion forces. Low MP, low density lighter. Uses: garbage bags, cling wrap. HDPE (hard plastic): Little side branching so chains are closely packed. Dispersion forces are stronger because electrons are closer together. High MP, high density. Produce rigid, less transparent polymers. Uses: plastic crates, rubbish bins, water pipes. Formation of Polyethylene 1. Initiation: A chemical called an initiator starts the reaction by opening the double bond of an ethylene monomer. This forms an ethylene free radical LDPE. For HDPE Ethylene molecules are activated on the surface of a peroxide catalyst. A free radical has an unpaired outer shell electron so is very active. 2. Propagation: The chain is lengthened when monomers join. 3. Termination: Free radical ethylene chains combine, a complete polyethylene molecule is formed and the process stops (it is terminated). Identify vinyl chloride and styrene as commercially significant monomers by both their systematic and common names. Name of Polymer Common names of Monomer Systematic name of monomer Recyclable plastic symbol Polyethylene Ethylene Ethene 2 HDPE, 4 LDPE Polyvinylchloride (PVC) Vinyl chloride, Chloroethene Chloroethene 3 V or PVC Polystyrene Styrene, Vinyl benzene Phenylethene 6 PS

3 Polyvinylchloride and polystyrene are both addition polymers. MEMORY TECHNIQUE: The common name is the polymer name without the prefix poly. Describe the uses of the polymers made from the above monomers in terms of their properties. Polyethylene uses: Insoluble in water- drink, milk, detergent containers. Stable and inert- Food containers. Easily processed into flexible film- cling wrap. Tough and strong- Boats, laundry baskets. Thermoplastic (can be moulded when heated and hardens when cooled). o Discuss the commercial and industrial importance of polyethylene: Can be used for a large number of different products domestically and industrially, e.g. cling wrap, pipes, storage containers. Is manufactured relatively cheaply. Is safer and more convenient than glass. Vinyl chloride must be treated with extreme care because it is flammable, explosion hazard. PVC Uses: o Weather resistant + insoluble and waterproof - indoor electrical conduit and underground water pipes, flooring and carpet backing. o Rigid- credit cards o It is thermoplastic- can be repeatedly melted and shaped o Pure PVC is hard and brittle, additives improve flexibility. Styrene: Polystyrene is Styrofoam which is formed by blowing gases through hot liquid. o Insoluble: drinking cups. o Easily formed to produce good thermal, sound & insulation properties, transparent sheets & pipes. o Crystal polystyrene- high stiffness, melts at 94C- used for CD cases, drinking glasses. o Very light (low density) and easily moulded - packing foam, foam egg cartons light weight saves costs of transportation. o Floats: buoyancy aid in small boats. o Durable (keeps its shape well)- cloth hangers. Discuss need for alternative sources of the compounds presently obtained from the petrochemical industry. Petrochemicals are chemicals made from compounds in petroleum or natural gas. Less than 5% of fossil fuel is used to make plastics and only a small percentage of that plastic is recycled. Fossils fuels have taken hundreds of millions of years to accumulate. Petroleum is non-renewable and supplies are running out but they cannot be replaced. Ethene is presently obtained from fossil fuels using about 3% of supplies which are non-renewable resources. Crude oil is the current source of fuels and petrochemicals including plastics. Crude oil is the source of monomers used to make most synthetic polymers. The rate of consumption is likely to increase as nations modernise and populations grow. This increasing demand increases pollution due to the use of petroleum increasing. Hence it is important to find alternative sources of energy. 84% of crude oil is used to produce energy but diminishing supplies means costs of crude oil are increasing. Polymers made from petrochemicals are non-biodegradable. Alternative sources that are renewable would be favourable as their use would prevent: o Facing the same problem of exhaustion that petroleum will be facing soon. Alternate sources are needed for ethylene and polymer production.

4 Production of Materials HSC Chemistry PRACTICAL Notes Gather and present information from first-hand or secondary sources to write equations to represent all chemical reactions encountered in the HSC course. Hydrogenation Hydration: catalyst is dilute sulfuric acid Halogenation: Hydrohalogenation: Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water. Alkanes react slowly by the process of substitution. Alkenes react rapidly, usually by the process of addition. Aim: To compare reactivities of alkanes & alkenes with bromine water & acidified potassium permanganate. Equipment: Bromine water, Cyclohexene, Cyclohexane, Potassium permanganate, Test tube rack, 6 test tubes, 2 unknown samples, Pipette Procedure: In schools labs, ethylene and ethane are 1. Add a squeeze of cyclohexane to a test tube. not often used because they are gases. 2. Add a squeeze of bromine water to the same test tube 3. Add a squeeze of cyclohexene to another test tube 4. Add a drop of bromine water. 5. Repeat above steps but replace bromine water with potassium permanganate Safety: Bromine water is poisonous and corrosive and should be handled with care, as should the acidified potassium permanganate solution. If contact with skin occurs, wash immediately. Cyclohexane and cyclohexene are volatile and poisonous. Experiment should be done in fume cupboard and waste must go into organic waste bottle. Results: Sample Reaction with bromine water Reaction with acidified KMnO8 Hydrocarbon (alkane, alkene) A Stayed amber coloured Stayed purple Hexane B Turned clear coloured (reaction occurred) Turned brown Hexene Hexene + Bromine 1, 2-dibromohexane. Conclusion: Through the experiment, it can be concluded that hexene was more reactive than hexane, thus alkenes are generally more reactive than alkanes. The reaction can be determined by the changing colour of the solution. Alkanes have only single bonds between carbon atoms, hence in the Absence of UV light, bromine in aqueous solution does not react with alkanes. Reaction of Bromine water with hexene: CH 2=CH 2 + BrOH (aq) CH 2BrCH 2OH

5 Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process. Using a model kit 1. Construct 6 ethene monomers using 2 black balls (carbon) and 4 while balls (hydrogen). 2. Break the double bond of 1 monomer to form the reactive intermediate stage. 3. Attach the reactive intermediate to a second monomer to form a reactive dimer. 4. Repeat this process to build up the chain. 5. Repeat steps 1-4 for the other monomers- chloroethene and styrene. Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. Name specific enzyme(s) used or organism used to synthesise the material and evaluate the use/potential use of the polymer produced related to properties. Biopolymer: Naturally occurring polymers made using renewable resources, usually plants or microorganisms. E.g. Polyhydroxybutyrate- PHB Enzyme or organism used to synthesize the material: Alcaligenes eutrophus. Production: 1. Alcaligenes eutrophus bacteria are placed in an environment favourable to its growth (high nitrates, phosphates and other nutrients) so that it multiplies rapidly and grows in a large community. 2. The bacterial colony is then placed in a nitrogen deficient environment to change and restrict its diet. Under these conditions, the organism is no longer able to increase its population but instead begins to make the desired polymer which it stores for later use. 3. The organism is then harvested and the polymer is separated out. Desirable Properties: Renewable Biodegradable- useful for making disposal items with a short life span (e.g. nappies, plastic bags) Biocompatible (with blood and tissue)- can be used medically (e.g. stitches which dissolve, surgical implants). Stiff and brittle- packaging deep drawing articles especially in food industry (e.g. bottles, laminated foils and fishnets). Easily moulded Thermoplastic properties (Heat to mould, cool to harden). Advantages: Biodegradable: unlike polyethylene and other petroleum derived plastics, and so will help to reduce levels of rubbish in landfills. It is compatible with organisms (biocompatible); it is not rejected by the body s immune system and so can be used safely. Renwable High MP- 175 C High tensile strength- 40 MPA Non-toxic Insoluble in water Resistant to UV light.

6 Disadvantages: The production process is far too expensive. Large colonies are needed. It may become thermally unstable during processing which decreases production efficiency as well. Evaluation: PHB has enormous potential to be used commercially due to its biocompatibility and biodegradability but if production costs aren t lowered and colony numbers are not increased, it will not be economically viable. Process information from secondary sources such as molecular model kits, digital technologies or computer simulations to model: The addition of water to ethylene Aim: to model the hydration of ethylene using molecular model kits. Equipment: Molecular model kits. Method: 1. Create a model of ethylene using 2 black balls double bonded together and attach 2 hydrogen atoms to each of the black balls. 2. Create a model of water, using a red ball to represent oxygen. 3. First remove one of the bonds that connect the carbon atoms. Next, detach a hydrogen atom from the water molecule and connect it to the former double bond so that 1 carbon atom will have 3 hydrogen atoms. Attach the OH group to the other carbon atom. The dehydration of ethanol This is the reverse of the previous reaction 1. Remove the OH group from the carbon atom, and the bond that holds them together. 2. Remove a single hydrogen atom from the other carbon (leaving the bond behind). 3. Join the OH and H together to form a water molecule. 4. Re-attach the 2 carbon atoms forming a double bond. Advantages of model kits. o Allows us to represent the process of bond breakage and formation that occurs in these 2 reactions. o Provide a visual representation of the reactions, rather than the linear chemical equations that are usually written. Disadvantages: o Cannot see relative sizes or the properties. o Models cannot perfectly re-create the shape of the molecule because there are only certain places for where the sticks can attach to the ball. o Ball and stick models cannot represent polarity. o Cannot see where the electrons are shared. Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane. There are 2 main processes involved in the production of ethanol: collection of starch from the sugar cane and fermentation. Collection of Starch: 1. The sugar cane is crushed 2. The juice obtained is heated, clarified by the addition of lime and also by filtration. 3. The juice is evaporated to concentrate the sugar and then to begin the crystallisation process. 4. The syrup containing the sugar crystals is centrifuged in order to separate the crystals. (The resulting syrup residue is referred to as A molasses.