Production of Materials

Question 1

What is cracking?

Answer 1

The breaking down of higher molecular weight hydrocarbnons into more useful, lower molecular weight hydrocarbons

Question 2

Account for the high reactivity of ethylene

Answer 2

• The double bond in ethene is high in electron density, making ethene highly reactive.
• The second bond in the double bond is weaker, and thus requires less energy to break this bond and form two single bonds

Question 3

What are the four addition reactions ethene undergoes?

Answer 3

• Hydrogenation (+ hydrogen to form ethane) - over Pt catalyst at 150 degrees
• Hydrohalogenation (+ hydrogen halide to form haloethane)
• Halogenation (+ halide)
• Hydration (+ water to form ethanol) - with sulfuric acid

Question 4

What are the safety considerations for the bromine water experiment?

Answer 4

• Use small volumes of cyclohexane and cyclohexene and avoid flames as they are moderately toxic (eye and skin irritation) and highly flammable
• Bromine water is volatile and toxic by all routes of exposure so use diluted volumes and place in a dark fume cupboard
• Bromoalkanes are toxic by all routes of exposure so dispose of them in organic wastes bottles and handle with gloves

Question 5

Outline the method of the bromine water experiment

Answer 5

1. Perform experiment in a fume cupboard in the absence of UV light (to prevent alkane from undergroing slow substitution reactions)
2. Add 1mL of cyclohexane to two test tubes and 1mL of cyclohexene to two test tubes
3. Add three drops of red brown bromine water to one cyclohexane and one cyclohexene tube each
4. Shake all test tubes equally
5. Observe any colour changes

Question 6

Account for the results of the bromine water experiment

Answer 6

The test tube containing cyclohexene and bromine water turned colourless upon shaking. This is because cyclohexene contains a highly reactive double bond which can react with bromine water.

Question 7

Recall the chemical equation of cyclohexene with bromine water

Answer 7

Question 8

Justify your method for the bromine water experiment

Answer 8

• Cyclohexene and cyclohexane are liquids at room temperature, which are easier to manage than C1 - C hydrocarbons such as ethylene of propylene which are gases at room temperature
• Cyclohexene/ane were used instead of hexane/ene as cyclic hydrocarbons are more stable than their linear counterparts

Question 9

Justify the validity of the bromine water experiment

Answer 9

• All other variables such as UV light and temperature were controlled
• A control was used (test tubes with only hydrocarbons but no bromine water)
• The method tested the aim as cyclohexene was demonstrated to be mor reactive than cyclohexane
• Experiment could have made more valid if quantitative analysis was achieved using sensors and data loggers

Question 10

What are addition polymers?

Answer 10

Addition polymers are made by adding double bonded molecules to each other without the emission of any small molecules. The double simply opens and monomers attach.

Question 11

What are the conditions for LDPE?

Answer 11

• High pressures (100 - 300atm)
• High temperatures (400 - 600K)
• Using an oxygen containing catalyst (e.g. peroxide molecule)

Question 12

Describe the initiation process of LDPE manufacture

Answer 12

• The organic peroxide molecule splits into two peroxide radicals which contains an unpaired electron and thus is highly reactive
• The radical then activates an ethylene molecule by reacting with the double bond to form a single bond and attaching to one end of the ethylene molecule

Question 13

Describe the propagation process of LDPE manufacture

Answer 13

• This new radical will then continue to attack the double bond of another ethene and this process will then lead to a rapid sequence of addition monomers

Question 14

How does branching occur in LDPE?

Answer 14

As chains grow they can curl onto themselves so that the radical nears a hydrogen atom in the middle, which is subsequently captured, leaving a radical in the middle of the chain. This is called backbiting and occurs every 50 atoms or so to cause branching in LDPE.

Question 15

Describe the termination process of LDPE manufacture

Answer 15

• At various times, two free radical polymers can react with one another to form a covalent bond and a longer chain.
• Chain termination occurs randomly so the length of the polymer chains vary greatly.

Question 16

Relate the uses of LDPE with its properties

Answer 16

• LDPE are composed of branched chains, and hence have relatively weak dispersion forces.
• Therefore they are soft, flexible with a low boiling point and a low density.
• Thus, they are used in food wrapping, plastic bags and squeeze bottles.

Question 17

Outline the conditions for HDPE manufacture

Answer 17

• Low temperatures (80 - 100 degrees)
• Low pressures (20atm)
• Uses an ionic Ziegler-Natta catalyst

Question 18

Outline the process of HDPE manufacture

Answer 18

• Ethene molecules are added to the growing polymer on the surface of the Ziegler-Natta catalst

Question 19

Relate the uses of HDPE with its properties

Answer 19

• HDPE is composed of unbranched chains of polyethylene that can pack closely together and hence share relatively strong dispersion forces
• Hence, they are harder, more rigid than LDPE with a higher melting point and are used in garbage bins, pipes and opaque bottles

Question 20

Identify two commercially significant monomers by both their common and systematic names

Answer 20

• Vinyl chloride (chloroethene)
• Styrene (ethenylbenzene)

Question 21

Relate the uses of PVC to its properties

Answer 21

• Pure PVC is not very useful as it is hard and brittle and tends to decompose when heated due to the C-Cl bond
• Additives can be added to form a more rigid PVC which is lightweight, high strength, relatively unreactive and impermeable to water
• Hence, PVC is used in kitchen utensils, floor tiling, credit cards and underground water pipes

Question 22

Relate the uses of polystyrene to its properties

Answer 22

• Polystyrene is a durable, lightweight polymer that is a good insulator and able to keep its weight.
• As such, polystyrene can be used in CD cases and clear plastic drinking classes
• Softer form of polystyrene is manufactured by blowing gases through hot polystyrene liquid prior to cooling and solidification
• The gas bubbles cause polystyrene to be an excellent lightweight insulator and a highly spongy material
• Therefore this form of polystyrene is used in drink cups, bean-bag filler, and packing materials

Question 23

Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry

Answer 23

• Petrochemicals are chemicals obtained from petroleum, which is a fossil fuel
• Fossil fuels are non-renewable, that is, thaey cannot be replaced once used in a reasonable timeframe
• Scientists estimate that oil supplies will run out in the foresseable future at this rate.
• They also argue that petroleum will gradually become more expensive as supplies diminish which means cost of manufacturing plastics will become prohibitive in the future
• Therefore, to meet energy and material needs in the future, alternative sources will be needed

Question 24

Outline the nature of condensation polymers

Answer 24

• They release small compounds such as water during polymerisation when function groups from two or more monomers react and join
• No initiator molecule is required in condensation polymerisation and no double opens up to react
• The type of end product is dependent on the number of functional end groups of the monomer which can react

Question 25

Describe the structure of cellulose

Answer 25

• Formed from the condensation polymerisation of cellulose, where a water molecule is released for every joining of two water molecules
• The structure of cellulose is alternating flipped glucose molecules

Question 26

How can cellulose be used to produce petrochemicals?

Answer 26

• Cellulose contains the basic carbon-chain structures needed to build petrochemicals
• Cellulose can be converted to glucose by acid hydrolysis
• Glucose can then be fermented with yeast to produce ethanol
  
  • C₆H₁₂O_6(aq) -> 2C₂H₅OH_(l) + 2CO_2(g)
• The ethanol can then be used as a fuel on its own or dehydrated to ethene with concenrtated sulfuric acid
  
  • C₂H₅OH_(l) -> H₂O_(g) + C₂H_4(g)
• Ethene is the main raw material in the production of petrochemicals being used to produce polyethene and other plastics

Question 27

Outline the advantages of using cellulose as a raw material to produce petrochemicals

Answer 27

• Cellulose is a renewable resource which is significant in the face of diminishing supplies of fossil fuels to produce petrochemicals with
• Cellulose is widespread and hence sources of petrochemicals would be local, reducing financial and energy costs of transportation
• Cellulose is biodegradable, and thus there is scope for the production of biodegradable polymers which are derived from cellulose. They have a much smaller impact on the environment. Positive impacts include reducing rubbish levels in landfills, healthier ecosystems and better waste management

Question 28

Outline the disadvantages of using cellulose as a raw material

Answer 28

• In the process of converting cellulose to ethene to use as a raw material (describe in an exam), the current costs are several times more expensive than simply sourcing raw materials from crude oil, due to added costs of tending, harvesting and then converting the crops
• The high quantity of energy requried would also come from fossil fuels and thus more fossil fuels would be used to produce ethylene from cellulose than if petroleum was simply cracked to ethylene, as well as increased release of greenhouse gases
• There is also a loss of arable land in which the crops can be grown. Problems such as leaching, salinity and erosion can also result.

Question 29

Recall the name of a biopolymer that is not cellulose

Answer 29

Biopol, which is a copolymer of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid where each monomer alternates. The systematic name for biopol is poly-3-hydroxybutyrate-poly-3-hydroxyvalerate

Question 30

How is biopol produced?

Answer 30

• In industrial production, the ralstonia eutrophus bacteria are grown in an environment with carbon based food source and limited nutrients such as nitrogen and phosphates
• When bacteria levels are high enough, the environment is changed so that it is high in glucose and valeric acid but still low in nitrogen
• This causes bacteria to produce PHBV in their cell walls.
• The extraction of biopol involves dissolution in hot CHCl₃and centrifugation to remove solid waste and then extracting the polymer as a powder

Question 31

What are the advantages of using biopol?

Answer 31

• Biopol is a biodegradable material, so it has a smaller impact on the environment. It will reduce rubbish levels in landfills and leads to healthier ecosystems and better waste management. It can replace polypropylene in disposable products such as fast food utensils and paper plates
• It is a biocompatible material, which can be dissolved by enzymes in the body. This means that any surgical applications do not have to be removed from the body and has alowed for surgical materials which would otherwise be very difficult to use.
• It is renewable as it is sourced from biomass which can be replaced in a reasonable timeframe, in the face of diminishing fossil fuels.

Question 32

What are the disadvantages of using Biopol?

Answer 32

Biopol is currently very expensive to manufacture and demand is not high enough to be economically viable at the moment

Question 33

What are some recent developments in the production of Biopol?

Answer 33

• Gene slpicing techniques have allowed scientists to place the gene from ralstonia eutrophus into E. Coli bacteria, which grows much more quickly than Ralstronia Eutrophus, making the manufacturing process cheaper and faster
• Scientists have recently discovered that genetically engineered plants such as cress and potatoes can be made to produce biopolymers. Genes can be taken from microorganisms that make PHB naturally, then inserted into plants so the production of PHB would be cheaper

Question 34

Describe the dehydration of ethanol to ethylene

Answer 34

• Ethanol is heated with excess concentrated sulphric acid as a catalyst.
• The -OH group is removed, a hydrogen atom is removed from an adjacent carbon atom which form a water molecule
• This leaves the adjacent carbon atoms with an unfilled outer shell, changing their C-C single bond to a C=C double bond

Question 35

Identify the need for a catalyst in the dehydration of ethanol

Answer 35

• A catalyst is needed because the ethanol molecule is stable and will not spontaneously break bonds to released a water molecule to form a double bond
• Concentrated sulphuric acid is used as it absorbs water very well and thus an excellent dehydrating agent

Question 36

Describe the addition of water to ethene and the need for a catalyst

Answer 36

• The catalyst in the addition of water to ethylene is dilute sulfuric acid, as water is not strong enough to attack the electrons in the ethylene double bond.
• However, only dilute sulfric acid is required as the double bonds are highly reactive and do not require a large amount of energy to break

Question 37

Account for the many uses of ethanol as a solvent for both polar and non polar substances

Answer 37

• Ethanol consists of a hydroxyl group (-OH) at one end of the molecule, which is polar and can form dipole-dipole, dipole-ion, and hydrogen bonds with other polar substances and hence easily dissolve them
• The alkyl group at the other end of the molecule is non-polar and can share dispersion forces with other non-polar molecules such as haxeane and oils
• Hence, many non-polar substances that are not soluble in water are soluble in ethanol, which is why ethanol is widely used as a solvent
• It is also the least toxic alkanol

Question 38

What products are ethanol used as solvents in?

Answer 38

• Dyes
• Food colouring
• Perfumes
• Varnishes

Question 39

Describe the conditions under which fermentation of sugars is promoted

Answer 39

• Suitable source of sugar mashed up with water (sugar cane, fruits)
• Approximately 37^oC for efficient yeast action, rate of reaction and tolerance
• Anaerobic conditions (absence of oxygen) to prevent oxidation of ethanol
• Presence of yeast

Question 40

Summarise the chemistry of the fermentation process

Answer 40

1. Yeast is mixed with mashed up grain and water
2. The enzymes in yeast break down the larger carbohydrates (e.g. starch and sucrose from cane sugar waste or molasses) into simple carbohydrates (glucose and fructose)
3. In an environment with all the conditions for fermentation, the enzymes in the yeast break down glucose into ethanol and carbon dioxide
4. The fermentation process stops at around 15% ethanol concentration as the ethanol starts killing the yeast
5. Fractional distillation of the mixture can achieve higher ethanol concentrations (up to 96%)

Question 41

Summarise the industrial production of ethanol from sugar cane

Answer 41

1. Harvested sugar cane is crushed to create pulp of cellulose and sucrose
2. Pulp is heated to 100^oC and dilute dulfuric acid is added
3. This hydrolyses cellulose and sucrose molecules into glucose
4. The glucose is hydrolysed with stronger acids and filtered again
5. Calcium hydroxide is added to neutralise the sulfuric acid to form an insoluble calcium sulfate which is removed through filtration
6. Water is added to reduce concentration of glucose to around 40% and acid is added to make pH around 4-5 for fermentation
7. Solution is placed in an oxygen free tank at around 37^oC and yeast is added to start fermentation
8. CO₂ evolved from the fermentation process is captured and purified to sell to industries such as soft drink companies
9. After 2 days, the mxiture reaches around 10-12% concentration
10. Mixture is then distilled to achieve higher concentrations of ethanol

Question 42

What are the advantages of using ethanol as an alternative fuel?

Answer 42

• Ethanol is renewable which is important in the face of diminishing petroleum fuels which are non-renewable
• Ethanol that is sourced from biomass is theoretically carbon neutral. As the same number of moles of carbon released in the combustion of ethanol is absorbed during the photosynthesis of the biomass source.
• Ethanol requires less oxygen to completely combust then octane and is therefore less likely to combust incompletely, reducing the production of toxic byproducts such as carbon monoxide
• Spark plugs don’t have to be replaced as often as less carbon is deposited
• Ethanol has a lower boiling point than octane and is hence more volatile, and ignites more readily
• Ethanol can be sourced from local biomass production. Conversely, petroleum sources have to be often imported. Local sources reduce financial and energy transportation costs, improve local employment and increase stability of fuels

Question 43

What are the disadvantages of using ethanol as an alternative fuel?

Answer 43

• Existing car engines would require costly modifications to run on hydrous ethanol blends
• Anhydrous enthanol can be blended with fuel up to 24% ethanol without engine modifications
• Greater engine wear occurs with high ethanol-petrol blends as ethanol fuels require higher engine compression ratio
• Large areas of arable land would be required to produce renewable ethanol fuel, which would lead to greater environmental problems such as soil, erosion and deforestation
• The fermentation process is currently too expensive to operate on the large scale required for fuel use
• Ethanol releases less heat per gram than octane so ethanol is less energy efficient

Question 44

Evaluate the success of ethanol’s current usage

Answer 44

• Ethanol is predominantly used in fuel blends with petroleum, although hydrous ethanol blends of over 99% are available.
• In Australia, ethanol is subsidised by the government and significant quantities of fuel consist of 10% ethanol blends sourced from cane in northern Queensland
• The success of ethanol blends in Australia has been limited however as Public are suspicious of the damage that ethanol can cause to engines
• Brazil and US currently have highest use of ethanol in fuels.
• In Brazil, the government legislated that all fuels must consist of 25% ethanol
• A quarter of cars in Brazil run on hydrous ethanol, which has proven to be efficient
• Many states in US require all fuels to consist of at least 10% ethanol
• Hence, introduction of ethanol fuel blends have been quite successful
• Success of Brazil and US are only possible due to their vast areas of arable land, which may not be possible for other areas
• (state advantages.. then say possible more widespeare use in future as petroleum prices increase due to diminishing resources)

Question 45

Outline the method for fermentation of glucose and monitoring mass changes

Answer 45

1. 20g of glucose was mixed with 150mL of lukewarm (37^oC water and 5g of yeast
2. Pour the mixture into a 250mL side-arm conical flask and stoppered
3. The flask was weight on an electronic scale and then placed into a water bath at 37^oC
4. The flask was weight every 10 minutes until no mass change was observed
5. Apply steps 1 -4 but without yeast to serve as a control

Question 46

How do you test for the products of fermentation of glucose?

Answer 46

• Bubble released gas through limewater and if it turns milky, CO₂ is present
• Ignite a small volume with care, which will produce a colourless flame if ethanol is present

Question 47

Comment on the reliability of the fermentation experiment

Answer 47

• Glucose was kept at a constant temperature of 37^oC which improves the consistency of the investigation
• Could be made mroe reliable if experiment was repeated and an average mass loss was recorded

Question 48

Comment on the validity of the fermentation experiment

Answer 48

• The method tested the aim by monitoring mass changes
• A control was used
• Other variables such as temperature and pressure were kept constant
• Water bath ensured optimal temperature for fermentation
• Stoppered beaker allowed no extra mass to enter or leave apart from carbon dioxide
• Time of fermentation was relatively short, so mass loss due to evaporation was minimised

Question 49

Outline the method used to compare heats of combustion of at least three liquid alkanols

Answer 49

1. Light the first spirit burner
2. Adjust the height of the can so that the tip of the flame just touches the can
3. Replace the cap on the spirit burner to extinguish the flame
4. Weight the burner with its liquid contents and record
5. Add 200mL of cold water to the copper can using a measuring cylinder
6. Place a thermometer halfway in the water and record its initial temperature
7. Light the wick and stir the water gently with the stirring rod to ensure uniform heat
8. Monitor the temperature and extinguish the flame by replacing the cap when temperature has risen by 10^oC
9. Reweight the burner
10. Remove soot from the bottom of can and replace the water in the copper can before testing the next alcohol

Question 50

Why does 1-proponol have a higher heat of combustion than methanol?

Answer 50

Because more bonds are created in the formation of products of 1-proponol than methanol (creating bonds releases energy)

Question 51

Why were the observed molar heats of combustion less than the theoretical values? And how can these errors be minimised?

Answer 51

• There was not 100% efficiency in heat transfer between flame and can (a draught shield around the burner could reduce this)
• Soot under the tin can for 1-proponol indicated incomplete combustion, reducing the heat emitted
• Heat was lost from the water to the surroundings due to radiation and evaporation (a lid on the can would minimise this effect)

Question 52

MEMORISE BATTERY SHIT.

Question 53

What are the conditions for an isotope to be stable?

Answer 53

• Elements with atomic number < 20 should have N:P ratio of 1:1
• Atomic number 20 - 50 should have N:P ratio of 1.3:1
• Atomic number 50 - 83 (excluding 83) should have N:P ratio 1.5:1

Question 54

What are transuranic elements?

Answer 54

Elements with an atomic number of 93 or higher

Question 55

Outline the process of neutron bombardment with an example

Answer 55

• In induced nuclear reactors, the nucleus of an atom, called the target nucleus is combarded with electrons
• These bombarding particles may become incorporated within the target nucleus, creating a new unstable radioisotope with an increased mass number

Question 56

Outline the process of using particle acclerators with an example

Answer 56

• Transuranic elements can also be made using particle accelerators, where heavy nuclei are bombarded with high speed positive particles such as helium

Question 57

How are commercial radioisotopes such as Technetium-99m produced?

Answer 57

• On a commercial level, nuclear reactors are often used
• Cyclotrons may still be used but are significantly more costly
• Technitium-99m is produced by bombarding Molybdenum-98 with a neutron to form Molybdenum-99, which decays to form Technetium-99m
• It can also be produced by accelerating deuterium and bombarding it onto target Molybdenum-98 to produce Technetium-99m and an excess of electrons

Question 58

Identify instruments that can be used to detect radiation

Answer 58

• Photographic film
• Thermoluminescent Dosimeter
• Geiger counter
• Cloud gas chamber

Question 59

Relate the use of technetium-99m with its properties

Answer 59

• In medicine, technetium-99m is used to diagnose heart and brain diseases such as tumours
• Emitted gamma radiation is picked up by external equipment and converted onto an image on a projector as the radioisotope travels through the body, effectively tagging the desired areas
• It is used because it only has a half life of 6 hours, which is ideal as it minimises the patient’s exposure to the gamma radiation, which despite having low ionising strength, can still ionize bodily tissues and inhibit bodily functions
• It is also used ebcause it is versatile. For example, it can be combined with tin, allowing it to be transported through the bloodstream and detect bloodclots and other abnormalities

Question 60

Outline the benefits of using Technetium-99m

Answer 60

• It has reduced costs and provided a convenient, non-invasive method of diagnosis for society
• It has allowed for a greater understanding of diseases and infections

Question 61

Relate the use of cobalt-60 with its properties

Answer 61

• In industry, cobalt-60 has provided a non-destructive, non-contact way of gauging thickness and testing for faults in certain objects
• A source of cobalt-60 is first placed above a continuous stream of paper, plastic or metal, while a piece of photographic film is located underneath on the other side
• As the cobalt-60 is continuously emitting gamma rays which is picked up by the photographic film, any change in thickness of the stream of material would be reflected by changes in intensity of detected radiation
• Electronic signals are sent to a central computer which adjusts rollers to maintain a more consistent level of thickness
• Cobalt-60 is used because it is highly convenient and highly effective as it has a half life of 5.3 years and hence does not need to be replaced often
• It has a relatively low emission of gamma rays which limits the potential danger to anyone working with the isotope

Question 62

Describe a recent discovery of an element

Answer 62

• Darmstadtium was first created in 9/11/94 when four atoms of the element were detected by a nuclear fusion reaction caused by bombarding a lead-208 target nucleus with nickel-62 ions
• With dharmstadtium-269 having only a half-life of 0.17ms, it is highly unstable and decays almost immediately which accounts for difficulties in isolaying observable amounts of this element