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Catalysts can be used in the petroleum industry in the cracking of long chain molecules. What is the purpose of this catalyst?
(A) Increase in the yield of the products
(B) Increase in the rate of reaction
(C) Decrease the temperature required for the reaction to proceed
(D) Increase the energy produced as a consequence of the reaction
- (B) Increase in the rate of reaction
- Catalysts increase the rate of reaction by lowering the activation energy of the reaction.
Which if the following is a byproduct in the process of condensation polymerisation?
(D) Ethanoic Acid
- (A) Water
- Condensation of polymers consist of monomers with two electronegative substitutes, such as OH- or Cl-. Of the possible answers to this question, the only molecule that can be made from these substituent groups is water (H-O-H). The by product must contain at least one of these electronegative substituents - hydrogen and methane do not, and ethanoic acid is too large a molecule to be formed this way.
Vinyl chloride in the monomer from which polyvinyl chloride is built. What is the systematic name for vinyl chloride?
(D) 1,2 dichloroethane
- (C) Chloroethene
- The monomer vinyl chloride has the structure CH2=CClH. Its systematic name must contain the prefix 'eth', as there are two carbons, the root word 'ene', as there is a double bond between the carbons and the prefix 'chloro', as there is a chlorine substitute present. thus the name is Chloroethene. It is not necessary to add any numbers to designate the position of the chlorine, as there is only one substituent and only two carbons.
In the process of fermentation of glucose, how many moles of ethanol are produced for each mole of glucose?
- (C) 2
- The reaction for the fermentation of glucose is
- C6H12O6(l) --> 2C2H6O(l) + 2CO2(g)
- Therefore, according to the stoichiometric coefficients, for each mole of glucose present at the beginning of the reaction, 2 moles of ethanol are produced.
Cellulose is an important biopolymer and one which you have studied as part of your chemistry course. What is cellulose produced from during condensation polymerisation?
- (B) Glucose
- Glucose is the monomer of cellulose. Both cellulose and glucose occur naturally. the polymer made from A (Ethylene) is polyethylene and no polymers are made from either benzene or ethanol (answers C and D).
Ethanol has been investigated for some years as a potential alternative fuel source. What is one advantage of using ethanol as a fuel?
(A) Higher molar heat of combustion per kilogram than the corresponding alkane (ethane).
(B) Increase fuel efficiency (less fuel per kilometer) compared with petrol.
(C) Lower cost than petrol
(D) Lower nett levels of greenhouse gas emissions than petrol.
(D) Lower nett levels of greenhouse gas emissions than petrol
This is the best answer, as it is most important to society that ethanol would have lower greenhouse gas emissions than petrol
A student prepared a solution of potassium iodide. She then added a very small quantity or bromine water to the original solution. After some time she noticed a deposit of iodine crystals on the bottom of the beaker. Which of the following best explains the student's observations?
(A) The oxidation state of the iodine has gone from 0 to -I so the iodine has been oxidised.
(B) The oxidation state of the iodine has gone from 0 to -I so the iodine has been reduced.
(C) The oxidation state of the iodine has gone from -I to 0 so the iodine has been oxidised.
(D) The oxidation state of the iodine has gone from -I to 0 so the iodine has been reduced.
- (C) The oxidation state of the iodine has gone from -I to 0 so the iodine has been oxidised.The student began with KI, in which the iodide has an oxidation state of -I, iodine crystals were formed in which iodine has the oxidation state of 0 (an element in its standard state). This reduction in oxidation number is evidence of reduction of the iodide to iodine. An increase in oxidation number would be evidence of oxidation.
An iron nail was placed in a solution of copper sulfate. After some time the nail had been covered with a redish brown coating, and the blue colour of the solution had become lighter. Which of the following best explains these observations?
(A) The iron is a stronger reductant than the copper solution and hence the iron ions gain electrons from the copper in the solution.
(B) The iron is a stinger oxidant then the copper and hence the iron ions gain electrons form the copper solution.
(C) The copper is a stronger reductant than the iron hence copper ions gain electrons from the iron nail.
(D) The copper is a stronger oxidant than the iron hence copper ions gain electrons from the iron nail.
- (D) The copper is a stronger oxidant than the iron hence copper ions gain electrons from the iron nail.
- The copper ions are being converted to copper metal. The observation that gives rise to this conclusion is that the iron nail is being covered in reddish brown coating and the blue of the copper sulfate solution is disappearing. if the copper is being reduced (going from oxidation state +II to 0), then the iron must be undergoing oxidation (going from an oxidation state 0 to +II). As the copper is being reduced, it must be an oxidant and the iron a reductant, as it is being oxidised and causing the copper to be reduced. When the iron is oxidised, it loses electrons and these are gained by the copper ions in the solution. In terms of strength of oxidant, the species that is reduced is the stronger oxidant.
Carbon 14 is an unstable isotope because?
(A) It has a half-life of about 6000 years.
(B) Its nucleus has an atomic number greater than 83.
(C) The neutron to proton ration is too great.
(D) It has more neutrons than protons
- (C) The neutron to proton ration is too great.Many stable isotopes have a greater number of neutrons compared to protons. It is the ratio that is critical. However the ration for small atoms like carbon is very close to 1.0.
Neptunium-239 is a transuranic element produced by bombarding uranium-238 to form an intermediate product which then undergoes beta decay to for Np-239. What is the original U-238 bombarded with?
(D) Alpha Particles
- (A) NeutronUranium-238 has 92 protons while neptunium has 93. However, uranium is not bombarded with a proton. it is bombarded with a neutron and the nucleus then emits a beta particle.
Which of the following would be displaced from the solution by the addition of powdered iron?
- (C) Nickel
- The only metal in the answers that has a reduction potential smaller then that of iron (i.e. that is less reactive then iron) is nickel. The redox reaction of these two metals results in a positive voltage, which means a spontaneous reaction.
Cellulose is am example of a naturally occurring condensation polymer. What is the name of the monomer that makes up the cellulose molecule?
(B) Amino Acid
- (A) Glucose
- Glucose is the monomer of cellulose. Answer B is incorrect, as amino acids are the monomers of proteins.
The reaction below shows the dehydration of ethanol.
CH3CH2OH --> C2H4 + H2O
Which catalyst is required for this reaction to occur?
(C) Dilute sulfuric acid
(D) Concentrated sulfuric acid
- (D) Concentrated sulfuric acid
- The catalyst require for the dehydration of ethanol (and many other dehydration reactions) is concentrated sulfuric acid, The formation of the water as a product dilutes the sulfuric acid. Dilute sulfuric acid (C) is used as a catalyst in the hydration of ethylene to ethanol.
Which of the following is a significant source of ethylene?
(A) Fermentation of sugar
(B) Polymerisation of poly(ethylene)
(C) Cracking of long hydrocarbons
(D) Hydration of ethanol
- (C) Cracking of long hydro carbons
- Ethylene can also be produced by the dehydration of ethanol but not by its hydration.
Which of the following CANNOT be used to detect radiation?
(A) Photographic film
(B) Geiger-Muller counter
(D) Scintillation counter
- (C) Interferometer
- An interferometer is used to detect the interference pattern from light beams.
The reaction below shows the fission of U-235 in nuclear reactor.
01n + 92235U --> X + 3594Br + 301n
Which element is labelled X?
- (A) Lanthanum-139When radioactive decay occurs, the sum of the atomic numbers on the left and right hand side of the equation must be equal, and the same is true of the mass numbers. The equation is
- 01n + 92235U --> X + 3594Br + 301n
- The main source of error in this question is that the student may fail to multiply the mass number of the neutron by three on the right hand side of the equation, thus getting answer B.
Which two compounds listed below are significant byproducts of the catalytic cracking of petroleum?
(A) Propane and ethylene
(B) Chloroethane and chloromethane
(C) Water and ammonia
(D) Ethanoic acid and ethanol
- (A) Propane and ethylene
- Propane and ethylene are significant byproducts of the catalytic cracking of petroleum. The fractions of petroleum are hydrocarbons and are broken into smaller hydrocarbons when cracked.
What is the systematic name for polystyrene?
- (C) Poly(ethenylbenzene)
- The systematic name for polystyrene is poly(ethenylbenzene). The name of the monomer ethenylbenzene due to the presence of the ethenyl group (-CH=CH2) on the bensene ring. The polymer is named by adding 'poly' before the name of the monomer and brackets around the monomer name, making only one word. Answer D also look correct because benzene is often drawn in the format of 1,2,3-cyclohexatriene but this is not correct.
What happens when permanganate (MnO4-) is reduced to manganese (II) (Mn2+)?
(A)The oxygen gains electrons
(B) The manganese gains electrons
(C) the manganese loses electrons
(D) The oxygen loses electrons
- (B) The manganese gains electrons
- When permanganate is reduced to Mn2+ there is a reduction in oxidation number of the manganese from +VII to +II. This is a result of the manganese gaining 5 electrons.
Which of the following occurs in a galvanic cell?
(A) Oxidation occurs at the cathode
(B) Electrons travel from the cathode to the anode
(C) Electrons travel from the anode to the cathode
(D) Inert electrodes react to produce electrons
- (C) Electrons travel from the anode to the cathode
- In a galvanic cell, oxidation (loss of electrons)occurs at the anode and reduction (gain of electrons) t the cathode. Therefore, electrons must travel from the anode (loss) to the cathode (gain).
Which atom would be the least stable?
- (C) Hydrogen-3
- At low atomic numbers, the relationship between the number of protons and the number of neutrons is closest to 1:1. The least stable of these isotopes is hydrogen-3, as there are 3 times as many neutrons as protons present in the nucleus, which is a very large difference.
Ethene may be converted into poly(ethene).
What type of reaction is this?
- (D) Polymerisation
- Ethene (ethylene) is the monomer used in the production of the polymer poly(ethene) (polyethylene). No molecules are lost in the process.
Which of the following is a major component of biomass?
(C) Natural gas
- (A) Cellulose
- Biomass is largely composed of plant matter. Plant matter is largely composed of cellulose and lignin.
Which conditions would be best for the fermentation of sugars by yeast?
(A) Low oxygen concentration and a temperature between 25oC and 35oC
(B) High oxygen concentration and a temperature between 25oC and 35oC
(C) Low oxygen concentration and a temperature between 45oC and 60oC
(D) High oxygen concentration and a temperature between 45oC and 60oC.
- (A) Low oxygen concentration and a temperature between 25oC and 35oC
- The presence of oxygen will allow decomposing bacteria to colonise in the mixture.
What is the catalyst for the conversion of ethanol to ethene?
- (B) H2SO4Concentrated H2SO4 is the catalyst used to dehydrate ethanol, and dilute H2SO4 is used to hydrate ethylene.
Which statement concerning galvanic cells is correct?
(A) Oxidation occurs in the anode.
(B) They are also known as electrolytic cells.
(C) The cathode is assigned a negative charge.
(D) An external power source must be present.
- (A) Oxidation occurs in the anode.
- The anode is defined as the electrode where oxidation occurs no matter what the type of cell.
Which if the following is a transuranic element?
- (D) Curium
- Curium has an atomic number (96) beyond that of uranium (92). The others are not transuranic because they come before uranium in atomic number.
Which instrument is used to detect radiation from radioactive isotopes?
(A) pH meter
(B) Geiger counter
(C) Ion-selective electrode
(D) Atomic absorption spectrophotometer (AAS)
(B) Geiger counter
Refer to the Table of Standard Reduction Potentials to help you answer the following question.
A Galvanic cell was set up as below:
What would the reading on the voltmeter be?
- (A) +1.1V
- In order to determine which electrode is the anode (oxidation) and which is the cathode (reduction) one must consult a table of reduction potentials. The combination that gives the highest positive voltage is the spontaneous reaction (recalling that the sign of the voltage must be changed when the equation becomes an oxidation, rather than a reduction, half equation). in this case the equation for the oxidation of zinc is;
Zn --> Zn2+
and the equation for the reduction of copper is;
--> Cu E0
The overall voltage of the cell would be the sum of the oxidation and reduction half equation voltages, in this case E0cell = +1.1V
The diagram below shows a galvanic cell.
What does the anode in this cell consist of?
(A) Silver metal
(B) Silver nitrate
(C) Copper metal
(D) Copper nitrate solution
- (C) Copper metal
- The anode is the site of oxidation. In this galvanic cell the copper is being oxidised and the silver ions reduced, as copper is a more reactive metal than silver. Thus, the copper metal electrode is the anode.
The table gives the heat of combustion in KJ g-1 for a number of different fuels.
The heat of combustion in kJ mol-1 for one of the fuels was calculated as 2016 kJ mol-1.
What was the fuel?
- (C) Propanol
- MM (propanol) = 60 g mol-1, therefore = 60 x 33.6 = 2016 kJ mol-1.
Cellulose is a linear polymer which is a basic structural component of plant cell walls. Which is the correct representation of part of a cellulose polymer?
- Cellulose is a polymer made up of beta-D glucose monomers. When linked together, every second monomer must be inverted.
A student performed three tests to investigate the relative activity of metals. In each test a metal strip was placed in a solution containing ions of a different metal. The results are shown in the diagrams.
What is the order of activity of the metals, based on these results?
(A) X > Z > Y
(B) Y > X > Z
(C) Z > Y > X
(D) Z > X > Y
- (D) Z > X > Y
- A more active metal will displace another metal's ions in solution. Z is the most active because it displaces Y2+ and is not displaced by X. Y is the least active because it is displaced by X and Z.
Which polymer is made by the polymerisation of methyl methacrylate?
- The double bond opens up and carbons link up to form a long chain. Every second carbon atom will contain a -CH3 branch and a -COOCH3 branch.
Describe the main processes that occur during fractional distillation.
Crude oil is pre-heated before entering the fractionating tower. In the fractionating tower there are hundreds of bubble caps located on large trays that allow the separation.
More volatile components in petroleum bubble through these caps, rising higher up the tower or column where it is cooler. The compounds are separated as they go up the column because of their different boiling point ranges.
These compounds, or fractions, are drawn off at different levels in the tower.
Define the term 'cracking' in relation to the petrochemistry industry. Explain why this process is used.
Cracking is the process where high molecular weight saturated hydrocarbons are broken down into lower molecular weight hydrocarbons. These smaller hydrocarbons are often unsaturated. It is important because it can turn less useful fractions into more widely used shorter chain compounds. It can produce unsaturated hydrocarbons such as ethene. Ethene is the starting point for many important manufactured substances.
State the main difference between thermal cracking and catalytic cracking.
Thermal cracking achieves the process of breaking down long chain hydrocarbons by using very high temperatures. This is costly in terms of energy. By using suitable catalysts (catalytic cracking) the same effect can be obtained at lower temperatures.
(A) Write down the structural formula for propylene.
(B) From this formula, describe how propylene is different from ethylene Compared to ethylene, what would you predict about the boiling point of propylene?
(C) Explain how propylene and ethylene are similar.
(A) CH3CHCH2 or C3H6
(B) Propylene has an extra carbon and two extra hydrogen atoms. Its boiling point should be greater then that of ethylene as its molecule is larger.
(C) Both are unsaturated hydrocarbons, each with just one double bond and the ratio C:H is 1:2.
At around 500oC at moderately low pressures, C15H32 can be cracked to produce ethylene, propane (propylene), and octane. Write a balanced equation for this.
- C15H32 --> 2C2H4 + C3H6 + C8H18
Identify what makes ethylene so useful as a starting point for producing many industrial chemicals.
Its double bond has a high electron density making it very reactive to many chemicals, It is also small enough to act as the basic building block from which to 'grow' new compounds.
Give two examples of addition reactions with ethylene.
CH2CH2 + H2O --> C2H5OH
CH2CH2 + HCl --> C2H5Cl
Ethyl hydrogen sulfate, CH3CH2SO4H, is produced from ethylene by an addition reaction. Name the substance which is added to ethylene to form this.
After ethylene was reacted with a certain chemical it was oxidised. The oxidised product turned litmus red. Identify the chemical that reacted with ethylene.
Chloroethane was onced used to produce tetraethyl lead, Pb(C2H5)4, a petrol additive. The equation is:
Na + Pb + C5H5Cl --> Pb(C2H5)4 + NaCl
Balance this equation.
4Na + Pb + 4C5H5Cl --> Pb(C2H5)4 + 4NaCl
State how saturated fat hydrocarbons can be distinguished from unsaturated hydrocarbons.
Unsaturated hydrocarbons will rapidly decolourise bromine water. They also fade the colour of acidified permanganate solution.
In the reaction CH2CH2 + Br2 --> CH2BrCH2Br, name the compound formed.
Identify some precautions you need to take when working with bromine and hydrocarbons.
As bromine is toxic, using in it reactions should occur in the fume cupboard and you should wear gloves and goggles to prevent getting any of it on you. Hydrocarbons are flammable and should be kept away from naked flames and should not be disposed of down the drain when the experiment is concluded.
In the reaction:
5CH2CH2 + 2H2O + 2MnO4- + 6H+ ---> 5HOCH2CH2OH + 2Mn2+
(A) Name the compound HOCH2CH2OH
(B) Is this compound saturated or unsaturated?
(C) What can you say about the colour of the Mn2+ ion in solution?
- (A) 1,2-ethandiol OR ethan-1,2-diol
- (B) Saturated
- (C) The Mn2+ ion in solution is colourless, as is ethan-1,2-diol.
Explain dispersion forces.
Weak forces of attraction between uncharged molecules with full electron shells. The strengths of the force increases as that total number of electrons in the molecule becomes larger.
Explain why decane, C10H22, has a greater melting point than butane, C4H10.
As the length of the molecule increases there are more sites for these weak dispersion forces. Consequently, a greater force needs to be overcome before the substance will melt.
Two molecuels having the formula C5H12 have structures CH3CH2CH2CH2CH3 and CH3C(CH3)2CH3.
(A) The first is called pentane. The second is sometimes called neopentane. Give the IUPAC name for neopentane.
(B) Would both these compounds be expected to have a similar boiling points and pelting points? Explain.
- (A) 2,2-dimethylpropane
- (B) No. The molecular shape influences melting and boiling points. Depending in its packing, the strength of the dispersion forces will be affected.
Explain why ethylene is a good starting point for producing polymers.
It is a small molecule and its double bond can easily be opened to produce 'sticky' ends that can join with a whole host of compounds to form polymers.
(A) Define addition polymerisation.
(B) Explain how it differs form condensation polymerisation.
- (A) Polymerisation that requires two or more functional groups joined together by simple addition.
- (B) In condensation polymerisation a small molecule, usually water, splits out when two monomers join together. No such substance splits out with addition polymerisation.
Justify the procedure you used to compare the reactivities of an alkane and its corresponding alkene. Name the alkane, alkene and any reagents used.
Five drops of cyclohexane was added to 2 mL bromine water in a test tube and shaken. Decolourisation would indicate the presence of the double bond and identify the chemical as alkene. The investigation was repeated with cyclohexane and all variables such as volume and temperature were held constant so that a comparison could be made. This was carried out in a fume cabinet because bromine is volatile and poisonous. Cyclohexene and cyclohexane were used because the are liquids and as such are easier to handle than gases and they vary only by a double bond so that either variables will not influence the results. Bromine is used because it will readily react with a double bond but not single bonds.
Vinyl chloride and styrene are commercially significant monomers.
(A) Give the systematic name of vinyl chloride.
(B) Describe TWO uses of poly(styrene) in terms of its properties.
- (A) Chloroethene
- (B) It can be used as a packing material around electrical appliances when they are transported because it absorbs shock.
- It can be used to make foam cups for hot tea and coffee because its a good heat insulator.
Owing to its high reactivity, ethylene can be turned into poly(ethylene).
(A) What type of polymer is poly(ethylene)?
(B) Outline the steps in the production of high OR low density poly(ethylene)
- (A) Addition
- (B) Flor low density poly(ethylene), the reaction is initiated with an organic peroxide catalyst. The ethylene is subjected to extremes of temperature and pressure. Pressures of about 2600 atmospheres liquify the gas. The reaction container must be kept cool because the reaction releases large amounts of heat.The final product is extruded and formed into pellets which can be melted and moulded into products.
(A) Explain what is meant by the ream condensation polymer.
(B) Describe the reaction involved in the formation of a condensation polymer.
(A) A condensation polymer is a long chain molecule produced from smaller molecules (monomers) via the removal of a small molecule (often water)
(B) polypeptides are condensation polymers produced by the formation of successive peptide bonds between amino acids.
During your study of this module you evaluated the effectiveness of ethanol as a solvent.
(A) Identify the types of substances that dissolved in ethanol.
(B) Identify the property of ethanol that contributes to its effectiveness as a solvent for those substances.
(C) Ethanol can also be used as a fuel source.
i) Outline two advantages of using ethanol as a fuel source.
ii) Evaluate the success of ethanol as an alternative car fuel.
(A) The substance which dissolved in ethanol were mainly polar substances.
(B) Ethanol is a polar substances and since like dissolves like, ethanol dissolved the polar substances studied.
- i) Ethanol has a good octane rating. it produces far less nett greenhouse gases than petrol when combusted and it i a renewable source of energy. Countries that have no oil reserves may be able to grow sugar to make ethanol for fuel, thus saving on foreign currency.
ii) Ethanol is still in its developing/testing stage. It has shown good promise so far, with some local petrol stations blending it with their petrol, e.g Biogas. It has been phased in as an alternative fuel source in Brazil where it is proving efficient. Its high costs of production are a drawback at present and this has contributed to its lack of development in Australia.
During your study of this module, you carried out an investigation to compare the reactivities of alkane and their corresponding alkenes in bromine water.
(A) Describe the experiment you performed.
(B) Explain the results of your investigation.
(C) Justify the selection of the chemical substances chosen for this investigation.
(A) We collected a sample of the following alkanes in test tubes: hexane and cyclohexane. We also collected a sample of the following alkenes in test tubes: cyclohexene and hexene. We add some bromine water to each set of test tubes. We recorded any colour changes we could see in any of the test tubes.
(B) The alkanes did not react with the bromine water. The alkenes reacted with the bromine. We could tell because of the decolourising of the solutions. The halogens ass across the double bond of the alkenes hence the solutions decolourise as colourless 1,2-diobromo-alkane.
(C) We selected hexane and cyclohexane because they are both alkane s that are liquid at room temperature. It was necessary to select liquids in order to observe the colour changes upon addition of bromine water.
Name the starting material for the production of PVC.
Vinyl chloride (chloroethylene)
State whether the production of PVC from its monomer is an addition or condensation polymerisation reaction.
Explain why you should not burn PVC items.
Toxic fumes and poisonous HCl gas is liberated.
Explain how the physical characteristics of PVC can be modified for particular uses.
By selectively using additives in the manufacturing process.
Contrast the molecular structures of polystyrene and polyethylene.
Polyethylene is produces when two ethylene monomers combine but no extra atoms are needed. In polystyrene a benzene ring, minus one hydrogen, (a phenyl group) replaces a hydrogen atom on the ethylene monomer.
Summarise the properties of Styrofoam (polystyrene foam) which makes it useful for use as disposable foam cups.
It is light and it a thermal insulator for the hot liquids it is meant to hold. As Styrofoam is inexpensive to make, the cups are disposable and suitable for common use.
1. Fossil fuels provide both energy and raw materials such as ethylene, for the production of other substances.
- An ALKANE is a hydrocarbon with
- ONLY single bonds between the carbons.
- An ALKENE is a hydrocarbon with 1
- or MORE double bonds between carbons.
- Also recall:
1.2: 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.
- - When petroleum undergoes fractional distillation, some fractions, particularly petrol, are in demand and of high economic value. - Other fractions, consisting of larger molecules than in petrol and of low value, can be passed over a heated catalyst that cracks the larger molecules into smaller molecules.
- -- A major by-product of this catalytic cracking is ethylene.
- Ethylene (systematic name: ethene), C2H4,
- is one of the most useful substances in the petrochemical industry, and is in extremely high demand.
- - Ethene is the most widely used raw material for the production of synthetic organic products such as
- plastics, pharmaceuticals, insecticides and industrial chemicals.
Reason for Cracking:
- Cracking is the process of ‘breaking’
- large hydrocarbon molecules into smaller length chains, using heat (Δ).
- - Cracking always produces an alkane and an alkene
- - i.e. the cracking of pentane into ethylene and propane:
- - In refineries, the output of products DOES NOT match the economic demand; ETHYLENE is in very high demand, but it only makes up a very small
- percentage of crude oil.
- - To match the demand for ethylene, low-demand, long-chain hydrocarbons are ‘cracked’ and ethylene is produced.
- - There are two forms of cracking:
- - Catalytic cracking
- - Thermal cracking
- Catalytic Cracking:
- - In this process, carried out in a ‘cat-cracker’, long alkane molecules (C15 - C25) are broken into just two molecules, an alkane and an alkene.
- - This form of cracking uses a
- CATALYST to break the alkanes.
- - The catalyst used are zeolite crystals:
- - Zeolites are aluminosilicates (compounds made of aluminium, silicon and oxygen), with small amounts of metal ions attached. They are highly porous heterogeneous catalysts with a massive surface area
- - The reaction is carried out at 500°C, in the absence of air, with pressure just above atmospheric pressure.
- - This process uses less heat than THERMAL cracking, but it cannot decompose large molecules completely into ethylene, so it is insufficient in meeting the demands of the industry.
- Thermal Cracking:
- - Also called ‘steam’ cracking.
- - This process does not use a catalyst, only very high temperatures.
- - The long-chain alkanes are passed through metal tubes at temperatures of 700°C to 1000°C, at pressure above atmospheric.
- - The alkanes are decomposed completely into ethylene and other short chains.
- - The use of steam is that is allows for easy flow of hydrocarbon gases, it dilutes the mixture to create smooth reactions, and it removes carbon deposits in the metal tubes.
1.3: 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; It is a site of very HIGH ELECTRON DENSITY.
o This is very useful as it means that a variety of substances can be produced from ethylene.
- - The presence of a double bond
- allows atoms to be added to the ethylene molecule.
- o In this process, the double bonds between carbon atoms are broken and additional atoms or functional groups are added to either side of the double bond, resulting in the formation of a saturated hydrocarbon:
- These reactions that ethylene undergoes are known as ADDITION reactions, where one bond in the double bond is broken, and the two atoms in a diatomic molecule are ‘added’ on.
- There are many types of addition
- o Hydrogenation: Hydrogen is reacted with ethylene, using a platinum catalyst at
- 150°C. The product is ethane.
o Halogenation: Reactive molecules from the halogen group (Fl2, Cl2 and Br2) can all react with ethylene. EG: Chlorine molecule reacting with ethylene forms 1,2-dichloroethane.
- o Hydration: Ethylene is reacted with water, using phosphoric acid as a catalyst, to produce ethanol. This is an industrially important reaction.
- o Hydrohalogenation: In this reaction, a hydrohalogen (such as HCl or HFl) and
- ethylene react to form a halo-ethane. EG:
- HFl reacting with ethylene forms fluoroethane.
The MAIN advantage of the double bond is that ethylene can undergo polymerisation, a very important reaction that will be discussed later.
1.0.2: Identify data, plan and perform a first-hand investigation to compare the reactivity’s of appropriate alkenes with the corresponding alkanes in bromine water
There is a distinct difference between the chemistry of alkanes and that of alkenes. Alkanes react slowly, by the process of substitution; while alkenes act readily, by the process of addition. This difference in reactivity is used as the chemical basis for this experiment.
- Aim: to distinguish between an alkene
- and an alkane, based on its reactivity to bromine water.
- Accurately measure 1mL of cyclohexane and cyclohexene
- Pour each solution into two separate test tubes
- - Using a dropper, drop 3 drops of bromine water into each test
- Observe, record results
- - It was observed that cyclohexene turned the bromine water
- colourless, whereas the cyclohexane solution remained yellow.
- - Thus ONLY cyclohexene reacted with the bromine water, and thus the
- alkene was said to be more reactive than its corresponding alkane; this is due
- to the double bond of the alkene.
- Cyclohexene and cyclohexane were used, instead of ethylene or propene because C1 to C4 are gases at room temperature, and would be hard to manage; cyclohexene is liquid at room temperature.
- Also cyclohexene/ane was used instead of hexene/ane because cyclic hydrocarbons are more stable than their linear counterparts.
of the method:
- - The alkane reacted slightly, as UV radiation caused slow
- substitution reactions.
- - Bromine water is highly toxic if ingested, and is slightly
- - Cyclohexene and cyclohexane are both poisonous if ingested, and
- both give off fumes, as they are highly volatile and highly flammable.
1.4: identify that ethylene serves as a monomer from which polymers are made.
- - Polymerisation is the chemical reaction in which many identical small molecules combine to form one
- very large molecule.
- A monomer
is a simple molecule that can be bond to other monomers to form a polymer.
- A polymer
is a macromolecule containing repeating subunits, monomers, joined together with covalent bonds.
- Because of its reactive double bond, ethylene is able to undergo polymerisation; ethylene, a monomer, forms the polymer poly(ethylene).
1.5: Identify polyethylene as an addition polymer and explain the meaning of this term.
- - In an addition polymerisation reaction, no additional molecules (e.g. water) are produced – there is no gain or loss of atoms, the double bond
- simply ‘opens’ and monomers attach.
- - Polyethylene is an addition polymer, as the ethylene molecules combine with each other in the following way:
- - As can be seen, no extra molecules are produced. A more realistic representation of the polyethylene
- polymer (with nine repeating units) is:
1.0.3: Analyse information from secondary sources such as computer stimulations, molecular model kits or multimedia resources to model the polymerisation process.
- In this experiment, molecular modelling kits were used to show how polyethylene is produced through the polymerisation of ethylene.
- The class was divided into groups, and each group was provided with a kit.
- 3 ethylene monomers were created by each group, with black balls representing carbons and smaller, white balls representing hydrogen.
- Then the monomers were ‘polymerised’: each group combined their monomers with every other group until a large chain was created – a section of polyethylene.
o The models created a 3D representation of the chemical process, which led to greater understanding of polymerisation.
o The use of ball-and-stick models, depicting the double-bond with flexible rubber rods, greater increased understanding of the process.
of the method:
- o The model only provided a very limited section of a polyethylene
- molecule, as there were limited numbers of kits.
- o The use of catalysts (such as Zeigler-Natta catalysts) was not shown in
- the process, and thus it was not completely accurate.
1.6: Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer.
- Ethylene is a commercially and industrially important polymer.
- There are two methods for its production:
- o High Pressure Method: In this process, ethylene is subjected to pressures of 100-300 MPa, with temperature in excess of 300°C. A molecule, called the initiator, is introduced, usually a peroxide. The initiator starts off a chain-reaction, creating the polyethylene macromolecule.
- - This process creates BRANCHED chains of polyethylene that cannot be packed together tightly. Thus branched polyethylene is called low-density polyethylene (LDPE).
- o Ziegler-Natta Process: This process uses only a few atmospheres of pressure and temperatures of about 60°C. A catalyst is used: it is a mixture of
- titanium (III) chloride and a trialkylaluminium compound.
- - This process creates UNBRANCHED
- chains of polyethylene that can be packed together very densely. Thus unbranched polyethylene is called high-density polyethylene (HDPE).
- The steps taken to produce the polymer are the same in both methods, but the initiator molecule is different:
- o INITIATION: The initiator molecule is added to the ethylene container; in the diagram below, it is shown as a peroxide radical (an oxygen compound with a free electron). The initiator reacts with
- one ethylene molecule, breaking its double bond, and attaches to only ONE bonding site, creating an ethylene-initiator RADICAL. The “dot” represents a free, highly reactive, electron.
- o PROPAGATION: Another ethylene monomer
- attaches to this radical, opening another bonding site, then another attaches, and so on, rapidly increasing the length of the chain. One of these reactions:
- - Repeating this reaction many times gives a general formula:
- o TERMINATION: The reaction stops (terminates) when two such chains collide and the two radicals react, forming a longer chain. This is a random process, so the length of polyethylene chains can vary greatly. (The peroxide initiator is eventually engulfed by the reaction, and so is no longer present at termination):
1.8: Describe the uses of the polymers made from the above monomers in terms of their properties.
Low-Density Polyethylene (LDPE):
- o Plastic cling wrap/food packaging; because it is tough, flexible, transparent, non-toxic. As LDPE
- is permeable to O2 and CO2 but not to water these films keep foods fresh and prevent them from drying out.
o Disposable shopping bags; because it is cheap and relatively strong
o Milk bottles; as it is non-toxic, cheap, un-reactive and recyclable
o Insulation of wire and cables: non-conductor, reasonably strong
High-Density Polyethylene (HDPE):
o Kitchen utensils and containers; as it is strong and non-toxic
o Containers for petrol, oil, detergents, acids and solvents: chemical resistance, strong
o Rubbish bins; it is rigid, only slightly flexible and hard
o Pipes and other building materials; it is rigid, hard, and un-reactive
o Children’s toys, plastic buckets, lunch boxes and playground equipment: durable and tough
o Can be made into tough films, i.e. freezer bags.
Polyvinyl Chloride (PVC):
o Pure PVE is not a useful plastic as it is hard and very brittle and tends to decompose when heated; however, the inclusion of other additives to improve its flexibility and thermal stability greatly extended its range of uses.
o Garden hoses; it can contain UV inhibitors; it is relatively un-reactive, flexible, and durable. Can be softened with plasticisers.
o Pipes and guttering; it is very rigid and hard, and un-reactive. It is also easily shaped.
o Building industry for external cladding, guttering and down pipes, electrical conduit, waste water pipes, rigid panels and floor tiles: ridgid, hard, un-reactive, easily shaped
o Kitchen utensils, credit cards: strong, non-toxic
o Upholstery coverings for cars and furnishings, electrical insulation and garden hoses: can be made flexible
- o Bottles: impervious to oils and most
- organic materials
o CD cases, cassette tapes; used because polystyrene is transparent, brittle, hard, rigid, easily shaped, and is a good insulator.
o Screw driver handles and kitchen cupboard handles; very durable and strong, hard and inflexible.
o Using different production techniques can be used to produce products including computer and TV cabinets, wall tiles and study furniture.
o Packaging, and disposable cups; it is light (full of air), cheap, and it is a thermal insulator
o Boogie boards and the cores of surfboards: lightweight, cheap, low density
o Sound-proofing; it is a shock absorbent material, light, easily shaped, excellent insulator
2. Some scientists research the extraction of materials from biomass to reduce our dependence on fossil fuels
- - Addition polymers form NO extra molecules when their monomers join
- - This type of polymerisation reaction occurs due to a double-bond
- opening, creating 2 new bonding sites.
2.1: Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry
- There is an overwhelming need for alternative sources of compounds that are presently derived from the petrochemical industry (i.e. crude oil).
- This is because crude oil is a fossil fuel, and is hence a non-renewable resource.
- Based on current usage statistics, crude oil reserves could be completely used up within a few decades.
- The production of energy: 84% of crude oil is used to produce energy. This includes petrol and diesel for cars, heating oil, jet-engine oil and LPG.
- The production of materials: The other 16% is used to produce polymers, pharmaceuticals, and other extremely important chemicals.
- - Compounds obtained from the
- petrochemical industry have two uses:
- Some of the materials created from crude oil cannot be derived by any other ways (or would be much too expensive to synthesise), so once crude oil is exhausted, there will be no way to produce them.
- - It has been argued that alternative fuels be created so that crude-oil can be reserved for use by the
- petrochemical industry to create materials.
- The increasing cost of crude oil in this current day and age is another factor.
- Also, many countries that contribute a significant portion of the world’s crude oil are very economically and politically unstable, with fragile infrastructure, and supply from these countries can be very erratic.
- One of the most appealing replacements for crude-oil derived compounds is cellulose; this is because it contains all the carbon-chain structures needed for the production of materials, and it is so remarkably abundant on Earth.
2.2: Explain what is meant by a condensation polymer.
- A condensation polymer is a polymer that produces EXTRA molecules (usually water) when its monomers combine.
- Examples include natural polymers such as cellulose, starch, protein, DNA, and manufactured polymer fabrics such as silk, polyester and nylon.
2.3: Describe the reaction involved when a condensation polymer is formed.
- In condensation
, the monomers react differently than in addition reactions.
- There is no double-bond that opens (as in addition); the FUNCTIONAL GROUPS of the two monomers react together, forming a new bond and water.
- i.e. Cellulose:
Cellulose is a natural polymer formed through the polymerisation of glucose
- o Glucose, C6H12O6, is the monomer in this
- o The reaction occurs between 2 hydroxyl groups, forming a glycosidic bond
As can be seen, the reaction sites are the hydroxyl (OH-
) groups on the first and fourth carbons (C1 and C4).
Each glucose molecule has 2 reaction sites; that is why it can polymerise.
One C-OH bonds to another C-OH, forming a C-O-C bond (glycosidic bond).
The left over H+ and OH- combine, forming water.
2.4: Describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass.
- Cellulose is a naturally occurring condensation polymer (a biopolymer
- It is the single most abundant polymer on Earth, making up about 50% of the total biomass of the planet (biomass is the mass of all organisms in a given area).
- - It is long polymer chain made of
- repeating glucose monomer units, which FLIP for every alternate glucose,
- as can be seen in the above diagram.
- - Above, the structure of glucose is quite cluttered. To demonstrate a section of a cellulose chain, a simplified form of glucose will be used.
- Glucose; in short-form:
It is assumed that at every corner, there is a carbon atom.
Hydrogen atoms are not shown, but are also assumed to be there, and are deduced by knowing that carbon makes 4 bonds.
- o Hence, the structure of cellulose can be shown as:
- As can be seen, it is a very linear molecule, due to its straight chains.
- The close packing of its beta linkage ribbons and the strong hydrogen bonds between them gives cellulose its great strength and rigid structure.
- The attraction between the hydroxyl (-OH) and hydrogen (-H) groups of the adjacent cellulose molecules result in the formation of hydrogen bonds which bind the molecules in a regular crystal-like lattice.
2.5: Identify that cellulose contains the basic carbon-chain structures needed to produce petrochemicals and discuss its potential as a raw material.
- The BASIC carbon-chain structures that are used to make petrochemicals are short-chained alkenes such as ethylene (2C), propene (3C) and butene (4C)
- Glucose, the basic structure in cellulose, is a 6C molecule.
- - Hence it has to potential to be
- transformed into the above compounds.
- The Potential of Cellulose as a Raw Material:
Although theoretically, cellulose can provide limitless amounts of renewable raw materials, this is currently too expensive and impractical.
This is because in order to derive ethylene, etc., from cellulose, firstly, cellulose must be broken into glucose (using either bacterial digestion or acidic decomposition), then fermented (with yeast) into ethanol and then dehydrated (using H2SO4) into ethene; this is a lengthy and expensive process.
Hence, cellulose has great potential, but is currently not economical.
2.0.1: Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties.
- - Name of Biopolymer: Biopol™
- o It is made of polyhydroxybutyrate
- (PHB) and polyhydroxyvalerate (PHV).
- - Organism Used:
- o Alcaligenes eutrophus (a bacterium).
- - Production:
- o In industrial production, A. Eutrophus is grown in an environment favourable to its growth to create a very large population of bacteria (such as high nitrates, phosphates and other nutrients).
When a sufficiently large population has been produced, the environment is changed to one that is high in glucose, high in valeric acid and low in nitrogen.
This unnatural environment induces the production of the polymer by the bacterium; the polymer is actually a natural fat storage material, created by the A Eutrophus in adverse conditions.
Large amounts of a chlorinated hydrocarbon, such as trichloromethane are added to the bacteria/polymer mix; this dissolves the polymer.
The mixture is then filtered to remove the bacteria.
The polymer is extracted from the hydrocarbon solvent as a powder, which is then melted or treated further to create a usable polymer.
- - Properties:
- o It is BIODEGRADABLE and BIOCOMPATIBLE
It is non-toxic, insoluble in water, permeable to oxygen, resistant to UV light, acids and bases, high melting point, high tensile strength
- - Uses in Relation to Properties:
- o It has many medical applications (e.g. biocompatible stiches that dissolve or are absorbed by the body)
Disposable containers for shampoo, cosmetics, milk bottles, etc., as it only takes 2 years to decompose back into natural components
Disposable razors, cutlery, rubbish bags, plastic plates, etc.
- - Advantages:
- o It is biodegradable, unlike polyethylene and other petroleum derived plastics, and so will help to reduce levels of rubbish in land fills
It is compatible with organisms (biocompatible); it is not rejected by the body’s immune system and so can be used safely
It is a renewable resource
- - Disadvantages:
- o It is currently very expensive, and currently the demand is not high enough for it to be economically viable
- - Future Developments:
- o Recently, the gene for producing Biopol polymer strands from the Alcaligenes Eutrophus bacteria was extracted and implanted into E. coli using genetic engineering techniques. E. coli bacteria are much easier to grow than other bacteria, and thus are cheaper.
- o Nutrient sources are starting to be derived from waste materials, such
- as molasses and other agricultural wastes. This greatly reduces costs.