Chemistry

Production of Materials

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 chemicals reactions as they are encountered.

Word equation – Hydrogen + Oxygen WaterBalanced chemical equation - 2H2(g)+O2(g)2H2O(g)

Identify the industrial sources of ethylene from the cracking of the fractions from the refining of crude oil.

Ethylene can be obtained from the fractional distilling of crude oil and natural gas. However this is not enough to meet the demand of the petrochemical industry. Therefore ethane is obtained by the cracking of larger hydrocarbon chains.

Cracking – the process where high molecular weight fractions of crude oil are broken in to lower molecular weight substances in order to increased the output of high demand products.

Catalytic cracking

This utilizes a zeolite( an aluminosilicate crystalline compound) . The reaction is carried out without the presence of air at temperatures of 500oc. The zeolite acts as a surface on which the reaction takes place. Zeolites absorb the hydrocarbon chains into their inner surface. Zeolites are affective catalysts due to their large surface are per unit mass as they have tunnels and cavities within the molecules. Catalytic cracking is insufficient to produce the ethane demanded by the petrochemical industry.

Steam cracking

Steam cracking is the major source of ethane. Alkanes and steam are passed through hot metal coils at 800 oc causing the alkanes to decompose completely into small alkenes such as ethene, propene and butene.

Identify that ethylene because of the high reactivity of its double bond, can be transformed into many useful products.

As an alkene ethane possesses an unsaturated double bond which can change into a single bond giving each carbon at the end of the double bond extra bonding capacity. This allows ethane to combine with a variety of molecules/atoms forming useful chemicals. Products of these reactions include ethanol, pharmaceuticals and insecticides. It can also form various monomers such as styrene for plastics.

Addition reaction – a chemical change where two new atoms/molecules are added across the double bond; one on each carbon at the end of the double bond. This converts the double bond into a single bond

- Hydrogenation – the addition of hydrogen to form an alkane. C2H4(g) + H2(g) C2H6(g)

Heating the reactants in the presence of a nickel catalyst.

- Halogenation – the addition of halogensUsed to distinguish between saturated and unsaturated hydrocarbons.C2H4(g) + Cl2(g)CH2Cl(g) –CH2Cl(g)

Ethane + chlorine 1,2 dichloroethaneUsing an iron(III) chloride catalyst.

- Hydrohalogenation – addition of hydrogen halidesCH2=CH2(g) + HCl(g) CH3-CH2Cl(l)

Ethylene + hydrogen chloride chloroethane

- Hydration – the addition of water to form ethanolC2H4 (g) + H2O(l) CH3-CH2OH(l)

Ethylene + water ethanolThis is done in the presences of a sulphuric acid catalystEthanol can be used as a disinfectant, anti freeze, drink, industrial solvent and alternate fuel source.

Identify ethene as a monomer from which polymers are madePolymerisation – the process where identical small molecules combine together to form one large molecule. The reactants are known as monomers and the product is a polymer.

Ethene is a monomer to the polymer polyethylene. It also undergoes substitution reactions with chlorine to form chloroethene which is used as a monomer for PVC. It can also be used to produce the monomer phenylethene from which polystyrene is made. .

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

Polyethylene is a polymer produced by the addition polymerisation of the monomer ethene. It has the structural formula (- CH2-CH2-)n.

Addition polymerisation – the process where identical small molecules are joined together in long chains in a way which all the atoms in the monomers are present in the polymer. i.e. there is no addition product. This involves unsaturated monomers with a c=c double bond joining together.

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

1. Extract crude oil2. refine crude oil3. fractionally distil crude oil and extract faction of ethene4. Crack long chain hydrocarbon in order to obtain more ethene

Low density polyethyleneEthene gas is heated up to high temperatures of 300oc and subjected to high pressure of 1000 to 3000 atmospheres. A peroxide initiator is then added to start the propagation of the reaction. This initiator is not a catalyst as it is absorbed into the polymer chain at 1 every 2000 to 3000 monomer units. The peroxide initiator splits at the O-O bond forming a free radical which attacks the double bond of an ethene molecule. The resulting molecule R-O-CH2CH2, itself a radical attacks the double bonds of other ethene molecules resulting in the addition of a –CH2-CH2- group. As the chains grow they curl back resulting in the radical removing a hydrogen atom from a CH2 group within the chain. This process of back biting causes branching. The reaction is terminated when two radicals meet together or a terminating agent is added. The resulting product has many branched chains which hinder the polymer molecules from stacking close together resulting in a soft flexible low density plastic with a low melting point.

High Density Polyethylene-Ethene is heatet to a temperature of 60oc at just a few atmospheres in the pressemce of a Ziegler-Natta catalyst. This catalyst which is a mixture of titanium(III) chloride and a trialkylaluminium compound forms unbranched polyethylene molecules which pack together in an orderly fashion. The catalyst acts as a surface on which the reaction happens. HDPE is more crystalline the LDHPE and harder but more brittle with a higher melting point.

Identify the following as commercially significant monomers

- vinyl chlorideCH2=CHCl also known as chloroethene. It undergoes addition polymerization to form poly(vinyl chloride) also known as PVC. - styrene

CH2=CHC6H6 also known as phenylethene. It undergoes addition polymerization to form polyphenylethene or Polystyrene as it is more commonly known.

Structure Common Name

Systematic Name

Common Polymer Name

Systematic Polymer Name

CH2=CHCl Vinyl chloride chloroethene Poly(vinyl chloride)

Poly(chloroethene)

CH2=CHC6H6 Styrene phenylethene polystyrene Poly(phenylethene)

Describe the use of polymers made from above monomers in terms of their properties.

LDPE is soft, flexible, low density, translucent, thermoplastics and impermeable to water allowing it to be used as films such as cling wrap, plastic containers, plastic bags and garbage bag. It is also an electrical insulator allowing it to be used as wire insulation.

HDPE is hard to semi flexible, high density, transparent/translucent and impermeable to water. This allows it t be used in pipes that carry natural gas, containers to hold oils, petrol, detergents and acids, children’s toys, plastic buckets, lunch boxes and playground equipment. It is also an electrical insulator allowing it to be used as wire insulation.

PVC is not particularly useful as it is hard, brittle and tends to decompose upon heating. However additives can be added to extend its flexibility and stability making it more useful the LDPE or HDPE. Rigid PVC is used in external cladding, guttering and down pipes, electrical conduit, waste water pipes, rigid panels and floor tiles. Kitchen utensils and credit cards are also made out of PVC. Flexible PVC is used in upholstery coverings for cars and furnishings, electrical insulation and gardening hoses. PVC is impervious to oils and other organic compounds and is used to make bottles that hold these materials. PVC is used to protect surfaces, transport and hold liquids because of its water fast nature.

Styrofoam is produced by blowing gas through liquid polystyrene until it froths to foam which is then allowed to solidify. The gasses trapped within Styrofoam are an excellent lightweight insulator. Styrofoam is used in cups, eskies, fast food containers and packing material. Styene can also be produced as a hard clear brittle plastic. It is clear as few crystals are formed within it and the benzene ring in its structure makes it more stiff.. This clear plastic is used to manufacture cassette and CD cases, clear plastic drinking cups Polystyrene is good for making cases as it is impact resistant and unreactive. By adding coloring and other additives styrene can also be made in computer and television cabinets, wall tiles and sturdy furniture.

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

Identify data, plan and perform first hand investigations to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water.

Saturated hydrocarbons do not react with bromine water. Unsaturated hydrocarbons undergo an addition reaction with bromine water causing the bromine water to lose its colour as the bromine reacts with the alkene.

Analyse information from secondary sources such as computer simulations and molecular model kits or multimedia resources o model the polymerisation process.

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 by the petrochemical industry.

Petrochemicals are chemicals derived from the factions of petroleum. Petroleum is a finite resource with Australia’s petroleum reserve to diminish in 35 years and our natural gas reserves to be diminished in125 years. Fossil fuels are finite as the take millions of years to form. The main use of these resources, 95%, is combustion for energy. To meet demand in the future alternative sources must be found. These can be petroleum products made from biomass such as biopolymers for plastics and ethanol for fuel. As petroleum supply diminishes it will cause prices to rise having adverse affects on the world economy also an alternate renewable fuel source is needed to meet energy needs in the future and reduce carbon emissions which is contributing to the enhanced greenhouse affect.

Explain what is meant by a condensation polymer.Condensation polymers are long chains formed by joining monomer units with the elimination of water or other small molecule when a pair of monomers join together.

Describe the reaction involved when a condensation polymer is formed.

Condensation polymerisation – the process where two functional groups of two molecules come together with the elimination of water or small molecule causing the two functional groups to be linked together.

E.g cellulose

HO-C6H10O4-OH HO-C6H10O4-OH HO-C6H10O4-OH

Becomes

-O-C6H10O4-O-C6H10O4-O-C6H10O4- + xH2O

alternatively it can be written n(HO-C6H10O4-OH)H-( O-C6H10O4)n-OH + (n-1)H2O

Describe the structure of cellulose and identify is as an example of a condensation polymer found as a major component of biomass

Cellulose is a polymer made from the monomer glucose. Glucose has the structural formula HO-C6H10O4-OH. It has 5 carbon atoms and 1 oxygen atom in a puckered ring with oh groups on 5 of the carbon atoms. The c-c bond is shown on the top or the bottom. When glucose is combined with cellulose the OH on the right hand C atom of one molecule combines with the OH of the left hand carbon atom of the next glucose molecule. Forming the -O-C6H10O4-O-C6H10O4- chain. Each alternate glucose molecule in the chain is inverted. This produces a very linear molecule caused by the c-o-c bonds. This is a condensation polymerisation as water is eliminated from the chain as an OH is taken from one molecule and a H from another. There are strong hydrogen bonds between lines of cellulose molecules giving it strength and rigidity. As the hydroxyl groups within cellulose are involved in hydrogen bonding between other cellulose molecules cellulose is not soluble in water.

Cellulose is the major component of plant and animal material known as biomassBiomass refers to the materials produced by living organisms.

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

Each glucose unit of cellulose has four carbon atoms joined together in a chain. Therefore it could be regarded as the basic structure of making the starting molecules for petrochemicals as most polymers are made from 3 carbon chain monomers. The carbon chains in cellulose can be changed into the chains present in petrochemicals if a micro-organism can be developed or found to decompose cellulose into glucose and then from glucose to 3or 4 carbon chains. However this process must not require excessive amounts of energy and is able to meet world demand. Cellulose has high potential as a raw material if this process can be found as cellulose is a renewable resource and replace our dependence on a finite supply of petrochemicals. Cellulose is currently used to make polymers such as rayon and cellophane. It can also be used as an alternative fuel through fermentation of glucose. Ethanol can be dehydrated to form ethene and thus replace our reliance on ethane obtained from fossil fuels to make plastics and other chemicals. This process however requires vast amounts of electricity which is fuelled by fossil fuels offsetting the gain. Thus in order for it to become viable technology must improve to make the process more energy efficient.

Use available evidence to gather and present data from secondary sources and analyse the properties in the recent developments and use of a named biopolymer. This analysis should name a specific enzyme or organism used to synthesise the material and an evaluation of the use of potential uses of the polymer used based on their properties.

Poly (hydroxyalkanoates) or PHAs are a group of biopolymers produced from glucose using a bacterial catalyst. The property of the polymer produced depends on the bacterial strain and the conditions under which the fermentation process takes place. The polymers can be either thermoplastics or elastomeric plastics. These polymers are originally used by the bacteria for energy storage but have been found to have potential to replace the oil based thermoplastics. PHA’s are more desirable than thermal plastics as they are renewable resources and do not have the same disposable problems as thermo plastics due to their ability to biodegrade.

The first PHA to reach the market was Polyhydroxybutyrate or PHD. It is synthesised by using the microbes Alcaligenes eutrophus or Bacillus megaterium. The bacteria are fed on glucose and can create polymers of up to 80% of their dried weight. These bacteria have undergone genetic modification in order to increase the yield of polymer. This has resulted in the price of production falling from $800 a pound in 1980’s to <$1a pound today. The glucose used is usually wastes from places such as sugar mills and milk processing. By controlling the carbon sources of the bacteria changes the properties of the given polymer. Originally the first PHB produced was too brittle to be of much use. However it was discovered that when propionic acid was added to the bacteria’s diet a new polymer was produced which was far more flexible. Polyhydroxybutyrate-hydroxyvalerate or P (HB-HV) is formed with the use of Alcaligenes eutrophus and is fed

precise proportions of glucose and propionic acid. The structure of this new polymer has Hydroxybutyrate and hydroxyvalerate molecules alternating in the chain at random. By making the polymer more flexible it has expanded the available uses of this polymer.

PHA’s are marketed under the name Biopol. These polymers have an elasticity of 5% to >10000% elongation at break, UV stability, water stable yet biodegradable in marine, soil, compost and waste treatment environments, excellent film forming properties from aqueous latex and environmentally compatible. PHA’s can be used as polymer performance enhancers, non-woven fabrics, film and fibre, adhesives and coatings, binders for metals, biodegradable packaging and water resistant coatings.They are increasingly popular due to two major characteristics that they posses. PHA’s are both biocompatible and biodegradable. Due to this biocompatibility they can be used in medical application such as capsules for controlled drug release, surgical sutures, bone plates and wound are without the fear of a reaction from the patient or the polymer being toxic. They have the potential to be used a structural materials in personal hygiene products and packaging applications. Although the cost of PHBV has fallen it is still far more expensive than normal petroleum based polymers. The fact that PHA’s are biodegradable makes them perfect for disposable packaging. It is currently used in cosmetic containers and commercial films and paper coatings. There is also researching to creating a biodegradable fishing net which will lead to decreased instances where sea creatures are caught in disposed

3. oxidation-reduction reactions are increasingly important as a source of energy.

Explain the displacement of metal from solution in terms of a transfer of electrons.

When a more reactive metal is places in a solution of a less reactive metal salt. The less reactive metal is displaced from the solution by the more reactive metals ions. Thus the less reactive metal is seen deposited on the surface of the more reactive metal. We see in the solution that the more reactive metal changes from a stable state into an ion in the solution. The less reactive metal ion that was originally in the solution becomes a neutral atom on the surface of the other metal. This is due to a transfer of electrons between the two metal atoms. The more reactive metal donates electrons to the less reactive ion. The atom of the more reactive metal becomes an ion and the ion of the less reactive metal becomes an element. The non metallic ion in the salt solution is a spectator ion as it does not participate in the reaction. The more reactive metal is oxidised and the less reactive metal reduced. The reaction occurs due to the fact that the less reactive metal has a greater tendency to gain electrons than the more reactive metal.

Identify the relationship between the displacement of metal ions in a solution by other metals to the reactivity series.

- The more reactive metal will change from an element to an ion- The less reactive metal will change from an ion to a neutral atom.

If a less reactive metal is placed in a solution of a more reactive metal no reaction will occur as the more reactive metal atoms are already ions.An activity series can be devised from these displacement reactions. Where the more readily a metal is oxidised the more reactive it is. A more reactive metal has a greater tendency to lose electrons and thus in a solution is oxidised while the less reactive metal ion gains an electron forming a neutral state.

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

Oxidation state – the number of electrons transferred to and from the neutral atom in order to get to that state.

Oxidation – the loss of electrons is a increase in oxidation number. It can also be a gain in oxygen loss of hydrogen.Reduction – the gaining of electron is a decrease in oxidation number. Gain of hydrogen loss of oxygen.

A neutral atom has an oxidation state of 0A compound has an oxidation state of 0. The sum of the oxidation states of the atoms in it is 0.

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

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

Galvanic cells consists of two half cells which contain an electrode immersed in an electrolyte solution. The electrolyte solutions are joined by a salt bridge which allows negative ions to migrate from one of the half cells to the other in order to neutralise the unbalance in charge. The electrodes are connected by an external wire to complete the circuit.

In one half cell oxidation occurs while in another reduction occurs. As reduction occurs at the cathode electrons are transferred from the cathode to the ions in the solution. At the same time oxidation occurs at the anode causing electrons from the anode to be taken away causing atoms to become ions. When the circuit is completed, by adding a salt bridge and a wire between the electrodes, electrons flow through the circuit.

Oxidation occurs at the anode where electrons are produced from neutral metal atoms forming ions. The anode is negative.

Reduction occurs at the cathode where electrons are accepted. Positive ions from the solution accept electrons forming neutral atoms. The cathode is positive.

Salt Bridge allows the migration of ions in order to rectify an imbalance of charge. The positive ions created from the anode migrate into the salt bridge while negative ions in

the salt bridge move to the oxidation cell. The excess of negatively charged ions in the reduction cell is rectified by positively charged ions from the salt bridge moving to the reduction cell and the negatively charged ions from the reduction cell moving into the salt bridge. A porous pot can be used to balance charge allowing ions to move between cells rectifying charge imbalances.

Daniel cell: zinc- copper cellOne half cell contains zinc anode immersed in zinc sulphate. The other half cell contains the copper cathode immersed with copper sulphate. The are connected by a salt bridge.

Anode| electrolyte: salt bridge: electrolyte| cathode.Zn|Zn2+

(aq) || Cu2+|(aq)Cu

Oxidation half reactionZn(s) Zn2+

(aq) + 2e-

Reduction Half reaction

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

Salt bridge – Filter paper containing KNO3

Movement of electrons

The Zinc oxidises releasing electrons theses electrons move through the wire connected the two electrodes. These electrons when at the cathode reduce the copper ions forming solid copper. This however causes an imbalance in charge within each half cell. As positive ions are created in excess at the anode and positive ions are taken away at the cathode. Therefore electrical neutrality is maintained by positive ions migrating to the cathode and negative ions migrating to the anode through the salt bridge.

Zn2+ moves from anode to cathode while NO2- moves from the salt bridge to the oxidation

cell. SO4- moves from the reduction cell to the salt bridge while K+ moves from salt

bridge to reduction cell.

Cell diagram

Single vertical line denotes a boundary between phases. The double vertical line donates a salt bridge through which ions can move.

Pt, H2(g) | H+ || Au3+ | Auo Anode is hydrogen gas bubbling over platinum electrode, in H+ solution.

Cathode is gold electrode dipping into Au3+ solution Pt, H2(g) | H+, Cl- | Cl2(g), Pt

o Cathode is hydrogen gas bubbling over platinum electrode. Anode is chlorine gas bubbling over platinum electrode. Both electrodes share a common HCl(aq) electrolyte. There is no double line || because there is no salt bridge.

Pt | I2, I- || Fe3+, Fe2+ | Pto Cathode is platinum electrode dipping into solution of iodine and iodide

ions. Anode is platinum electrode dipping into solution of Fe3+ and Fe2+ ions. There is no single vertical line | between Fe3+ and Fe2+ because they are in the same phase. Rather, the boundary between phases is between the platinum electrode, and the solution of both iron ions.

Function of a cell bridge- complete the circuit- Allow the migration of ions in order to maintain a balance of charge.

If one reactant is going from element to ionic form while the other is going from ionic to elemental two separate half cells are needed. This is because if they shared a common electrolyte the stronger reductant would automatically displace the weaker reductant.A common electrolyte solution can be used if both reactants are going from an elemental state to an ionic state as the reactants can’t react directly as they are physically separate.

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

Anode: the electrode at which oxidation occurs. It has a negative charge.

Cathode: The electrode at which reduction occurs. It has a positive charge.

Electrode: electrical conductors in contact with the electrolyte solution and connected to each other externally. They are an interface where oxidation and reduction occur.

Electrolyte: a substance which in a solution or molten conducts electricity; any substance that contains mobile ions which behaves as an electrically conductive medium.

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

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

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

In terms of- chemistry- cost and practicality- impact on society- environmental impact

In terms of: Lead Acid cell Fuel Cellschemistry Porous lead anode and compressed

insoluble lead(IV) oxide cathode submerged in dilute H2SO4

Anode oxidation:Pb(s) + SO4

2-(aq) PbSO4(s) +2e-

E = +0.356VCathode reductionPBO2(s) + 4H3O+

(aq) + SO42-

(aq)+2e- PbSO4(s)+6H2O(l)

E = +1.685VNet Process created +2.041V

Hydrogen diffuses into a carbon, nickel or platinum anode while oxygen diffuses into the cathode. The electrodes act as catalysts for a reaction with either an acidic or alkaline electrolyte.Acidic:Anode oxidationH2(g)2H+

(aq) + 2e-

Cathode Reduction O2(g)+4H+

(aq)+4e- 2H2O(l)

Alkaline electrolyteAnode OxidationH2(g) +2OH-

(aq) 2H2O(l) +2e-

Cathode reductionO2(g)+ 2H2O(l)+4e-4 OH-

(aq)

Theoretical e.m.f is 1.23v but this is difficult to obtain

Cost and Practicality

Lead cells are relatively heavy and produce relatively low power to their mass. The produce a relatively constant 2v and a large initial current which can be used to start a car. Lead cells can be recharged by reversing the current flow. Lead batteries are the cheapest battery that can be

The fact that the H+ or OH-ions must migrate through the electrolyte solution to the respective electrode is a limiting factor. Fuel cells have a large fuel efficiency for mass and produce water as a bi-product however fuel

produced for what they do. Lead sulphate is deposited on the electrodes during use this reduced the surface area of the electrode reducing the rate of reaction and eventually halting it. However this is dissipated when a current flows in the reverse direction. Lead Batteries last a maximum of 3 hours before they need recharging.

cells are expensive to produce.

Impact on Society

. However Lead batteries are the only reliable source of energy that is cheap and able to generate the large initial current needed to start a car motor. This has allowed for cheaper motor transport.

Fuel cells have been used in the space shuttle programs to produce energy and water for astronauts. They have great potential if cost is reduced as a power source of the future.

Environmental Impact

The use of lead based elements is destructive to living organisms. Sulphuric acid is also harmful to the environment however since lead batteries are rechargeable they can be reused minimising the need for disposal. The use of lead and lead based oxides can are toxic to all internal organs and the nervous system. It disrupts the development of the nervous systems and can leave children with learning disabilities

Non-polluting as the product is water. Hydrogen and oxygen reactants are plentiful. However hydrogen is explosive which is a hazard.

Solve problems and analyse information to calculate the potential requirement of named electrochemical processes using table of standard potentials and half equations