Production of materials

Research assignment: Production of materials:

1.Outline the importance of the cracking of hydrocarbons to our industrialised society: (4 marks)

Different methods made by oil refineries have been used for the cracking of hydrocarbons. By doing this they are able to produce short chain alkanes that can potentially be used for petrol, additives to petrol to improve its quality, hydrogen, and alkenes such as propene and ethene.

Originally, cracking of hydrocarbons was achieved by thermal cracking (Heating the fraction to a very high temperature in the absence of air). However, this process was difficult to control as in the production of end products the breaking would occur in various, commonly unwanted, places. The process is also very expensive due to the energy required.

A more recent development is now more commonly used for the cracking of hydrocarbons with the use of catalysts (catalytic cracking). This process is carried out by a ‘catalytic cracker' (as seen on right). This is a much cheaper and more simple process as it is able to be carried out at lower temperatures. It is particularly important to the petroleum processing industry as crude oil is a very complex material and contains many valuable hydrocarbon compositions.

3. Distinguish between stable and unstable (radioactive) isotopes and outline the way scientists decide whether a particular isotope will be stable or not (5 marks)

Atoms that have different mass numbers but the same atomic number are isotopes. Stable isotopes are not radioactive as they have never been observed to undergo radioactive decay. Unstable isotopes however, are radioactive and are able to spontaneously change their composition using radiation.

Scientists are able to decide whether a particular isotope is going to be stable or not by figuring out if it is radioactive or not. There are many different processes to do this. Radioactive emissions are able to be shown on photographic film, by an ionisation counter (the Geiger counter) and a Scintillation counter.

Photographic film is effected by radioactive emissions. Darkening of the film increases with the degree of radiation and length of exposure. This method is commonly used today for people working with radiation. A badge containing photographic film is able to show them the levels of exposure to radiation they've had.

The ionisation counter consists of a metal tube filled with argon gas. It works by allowing the radiation to ionise the argon gas, forming free electrons and positive ions. The cations and electrons produced are attracted to electrodes that conduct a current to a recording device. A small window at one end of this tube allows radiation to pass through. This radiation causes the argon atoms to be ionised. The argon ions and free electrons allow a current to flow between the electrodes. Each time this counter is exposed to radiation bursts of current are converted into audible clicks to measure the amounts of radiation.

The Scintillation counter is used based on the fact that some substances produce a flash of light when struck by ionising radiation. Electrons in these substances are excited by the radiation and emit photons of light when the electrons return to lower energy states. These flashes of lights are able to be counted electronically to measure the levels of radiation.

5. Discuss the advantages and disadvantages of using ethanol as a fuel or fuel additive for motor cars (5 marks)

Advantages:

-Ethanol is a renewable and sustainable energy source fuel when made from sugar.

-The technology to make ethanol from the fermentation of sugar is a well known process, and can be done.

-It is “greenhouse friendly” as the carbon dioxide released is exactly the same amount as what was absorbed by the plants during photosynthesis to make the sugar.

Disadvantages:

-If petrol was to be completely replaced with ethanol, sugar industry wastes wouldn't be enough. Large tracts of land would have to be dedicated to growing just sugar cane to supply for the ethanol industry. Brazil attempted to do this in the 1980's and failed, causing a disruption in their food industry.

-Current technology for ethanol production requires large amounts of energy for the distillation process. Fossil fuels are currently used for heating, and so the process is not as renewable/”greenhouse friendly” as it was originally thought to be.

-To use ethanol as a petrol, entirely new engines are needed to run on pure ethanol, and the cost to do this to car-owners and manufacturers would be very high.

6. Demonstrate the usefulness of radioisotopes in industry and in medicine (5 marks)

Radioisotopes have many different uses in medicine and industry.

Most of the radioisotopes produced by ANSTO are for medical applications. They are most commonly used as a diagnostic tool to provide information about the functioning of tissues and organs in the body, but in some cases are also used to treat tumours and diseased organs. This is able to work as many substances are prone to concentrate in certain parts of the body. By doing this, medical professionals are able to avoid invasive exploratory surgery.

Radionuclides are able to be chemically attached to a molecule used by a particular organ in the body to help medical professionals target that organ. For example; isotopes of iodine are able to be used to study the thyroid gland, and iron isotopes can be used to study blood cells. However, only small amounts of the radioactive substances are introduced to patients to minimise exposure of radiation.

Most commonly used medical radioisotopes include Technetium-99 and Iodine-131. Technetium-99 is a gamma emitter that accounts for more than 80% of isotopes used in medical tracer diagnosis. It is reasonably safe as it has a relatively short half-life (6 hours), reducing the patients exposure to radiation. It is most commonly combined with different compounds to enable medical professionals to study different areas of the body, for example; when added to a tin compound, it can be injected into the blood screen and attach to red blood cells. This allows doctors to trace where abnormalities in the heart and blood vessels are.

Iodine-131 is widely used to study and treat thyroid disorders. The thyroid gland is the only major user of iodine in the body. Diseases of the thyroid gland can be diagnosed by monitoring the uptake of iodine. Patients are given a drink of NaI solution containing some iodine-131. After a few hours, the uptake of iodine is able to be measured by scanning the patients throat with an ionisation counter. A normal thyroid gland will absorb around 10% of the iodine within a few hours, however if the thyroid has absorbed too much, or too little of this iodine there is likely to be a problem.

7. Describe, with a diagram, a galvanic cell that you have set up in the laboratory and explain the flow of electrons and ions through it; identify its anode and cathode (6 marks)

This galvanic cell is based on the reaction between metallic zinc and copper(II) sulfate. It is easily set up by partly immersing zinc and copper strips in 1 mol/L solutions of copper(II) sulfate and zinc sulfate respectively in separate containers. Each of these two parts consisting of a metal strip in an electrolyte solution are called half cells. These solutions are joined by a salt bridge containing an electrolytic solution such as KNO3. This salt bridge consists of filter paper saturated with KNO3. The salt bridge allows ions to move between each half-cell as it completes the circuit.

As the cell operates, the zinc strip slowly dissolves, while the copper strip gradually becomes coated with more copper.

8. Compare and contrast the physical and chemical properties of alkanes and alkenes (7 marks)

Alkenes are more reactive than alkanes due to their double bond. The carbon-carbon bond consists of a strong double bond and a weak bond. In a typical reaction, the weak bond will be broken down.

Both alkanes and alkenes are highly combustible. Alkenes burn with a luminous flame to give off carbon dioxide and water. The flame is luminous due to there being a higher carbon content in alkenes rather than alkanes.

Boiling points:

The increase in boiling points for both alkanes and alkenes increase with molecular mass. This is due to increasing dispersion forces between larger molecules.

Properties and dispersion forces:

Both alkanes and alkenes are non-polar molecules. This means that the electron charge is distributed evenly around the molecule as carbon-hydrogen and carbon-carbon bonds do this. The non-polar nature of hydrocarbons and the weak intermolecular forces that exist between these molecules determine many of the physical properties of hydrocarbons. This means chemical and physical properties between alkanes and alkenes can be quite simmiler.

Viscosity:

Both alkanes and alkenes become thicker as their molecules become larger. This property (viscosity), occurs because of the increasing dispersion forces involved. Straight chain hydrocarbons tend to have greater viscosities than branched chain hydrocarbons due to the greater surface area contact that can occur between the molecules.

Solubility:

Hydrocarbons are non-polar. This means they will dissolve in any non-polar solvents but will not dissolve in polar solvents such as water. When hydrocarbons are mixed with water, two layers form (like oil and water). Usually as liquid, hydrocarbons are less dence than water and will therefore form the upper layer.

Viscosity:

Both alkanes and alkenes become thicker as their molecules become larger. This property (viscosity), occurs because of the increasing dispersion forces involved. Straight chain hydrocarbons tend to have greater viscosities than branched chain hydrocarbons due to the greater surface area contact that can occur between the molecules.

9. Assess the need for alternative sources of chemical compounds presently obtained from oil (4 marks)

Fossil fuels such as crude oil are currently an important source of energy for industrialised countries, however, they are not renewable. These fuels are mixtures of hydrocarbons are burned in air or oxygen to release energy. Fossil fuels, particularly crude oil and natural gas are an invaluable source of raw materials for the petrochemical industry. About 95% of all synthetic carbon compounds, including plastics, resins and solvents, are derived from compounds from petroleum and natural gas. There is increasing discussion within the community about how these non-renewable resources should be used, and ways to create alternatives. The competing uses of fossil fuels present an argument of whether we should be using them as a source of energy or should alternative sources of energy be developed and petroleum, natural gas and coal be used for raw materials required for the production of many useful materials. Presently, over 90% of petroleum and natural gas extracted from the earth is used as fuels.

11. Outline the use of one radioisotope in medicine or industry and describe the properties that make it particularly suited for that use (4 marks)

Iodine-131 has two major uses. Its most common use is the treatment of many different thyroid disorders, however it may also be used (in larger doses) for radiation therapy to treat tumours in the thyroid.

Cancer cells are usually more susceptible to radiation than normal cells, making it easier to get rid of any cancerous cells without causing too much harm to normal cells. The radioactive iodine concentrates in the thyroid gland and emits beta particles and gamma radiation which is able to kill most of the abnormal cells.

Iodine-131's most common use is the treatment of different thyroid diseases and problems. The thyroid gland is the only major user of iodine in the body. Diseases of the thyroid gland can be diagnosed by monitoring the uptake of iodine, to do this, medical professionals are able to give their patients a drink of aNaI solution containing some iodine-131. After a few hours, the uptake of iodine is able to be measured by scanning the patients throat with an ionisation counter. A normal thyroid gland will absorb around 10% of the iodine within a few hours, however if the thyroid has not absorbed the isotope at this standard rate there is likely to be a problem.

16. Demonstrate the importance of ethylene as an industrial chemical (4 marks)

Ethylene is becoming more commonly used as its reactive double bond is an ideal starting molecule for synthesis reactions.

Ethylene is an important raw material and is responsible for the production of many huge range of synthetic carbon compounds and polymers including plastics (polyethylene), pharmaceuticals, insecticides and industrial chemicals.

Ethene is the most versatile and widely used raw material in the petrochemical industry. Due to its abundance in the atmosphere however, it must be produced from other hydrocarbons by “cracking”.

17. Discuss the benefits and problems associated with the use of radioisotopes in medicine (5 marks)

Radioisotopes in medicine have many advantages, but also many problems. These problems are mostly related to the damage that radiation can cause to living things.

Most of the radioisotopes that are produced by ANSTO are used as a diagnostic tool to provide information about the functioning of tissues and organs in the body, however in some cases are also used to treat tumours and diseased organs. This is able to work as many substances are prone to concentrate in certain parts of the body. By doing this, medical professionals are able to avoid invasive exploratory surgery, which is highly beneficial.

Alpha, gamma and beta radiation however can all cause normal cellular processes to be disrupted. The ionising ability of radiation is what is particularly dangerous. It can cause electrons to be removed from atoms and molecules, including biological molecules such as DNA and proteins, forming ions and radicals. In some rare cases, damage to DNA may lead to the development of cancer. For example, A beta emitter is chemically similar to that of calcium; it can replace it in the bones where it can cause bone cancer and leukaemia.

18. Describe the chemical structure and uses of three addition polymers (6 marks)

Polyethene:

Polyethene is most commonly used as a light weight plastic for items such as plastic bags as it is reasonably strong, and very cost efficient.

Ethene can be changed from a gas to a liquid by subjecting it to a high pressure. When the liquid ethene is heated in the presence of a catalyst, the ethene molecules join together to form a long chain or polmer called polyethylene (or polyethylene).

CH2=CH2

+

CH2=CH2

=

-CH2-CH2-CH2-CH2-CH2-CH2-

ethene

ethene

polyethene

Polystyrene:

Polystyrene comes in many forms, the most common of which being polystyrene foam (Styrofoam). Styrofoam is produced by blowing gas through liquid poly(styrene) until it froths up into a foam, which is then allowed to cool and solidify. Polystyrene finds uses as insulating cups, eskies, fast food containers and packing materials.

Polystyrene can also be produced as a hard, brittle, clear plastic. This form is used in the manufacture of audio cassette and CD cases and clear plastic drinking glasses.

Polyvinyl chloride (PVC):

PVC is not a very useful plastic as it is hard, very brittle and tends to decompose when heated. However, with various additives added its flexibility and thermal stability is able to extend the range of its uses. The production of PVC is now only exceeded by LDPE and HDPE. Rigid forms of PVC are widely used in the building industry for things such as external cladding, guttering and down pipes. More flexible forms of PVC are used mainly as upholstery coverings for cars and furnishings, electrical insulation and garden hoses.

CH2=CHCl

+

CH2=CHCl

=

-CH2-CHCl-CH2-CHCl-CH2-

Vinyl chloride

Vinyl chloride

PVC

20. Evaluate the claim that ethanol is a renewable fuel (5 marks)

As supplies of petroleum slowly disappear, ethanol is becoming one of the most widely looked at renewable energy source. Ethanol can be produced from the starch or sugars present in sugar cane, corn, wheat, maize and other cereal crops. Although there is no commercial method of obtaining ethanol from cellulose, large-scale production by fermentation of starch and sugars has been carried out for many years.

In the 1970's, the government of brazil began subsiding the production of ethanol by fermentation of sugar cane. This decision was designed to reduce oil imports and increase employment. Today approximately ¼ of all motor vehicles run on a mixture of ethanol containing up to 20% ethanol.

Cars running on ethanol up to 15% do not need any engine modifications, however some modifications are necessary for engines running on pure ethanol or high ethanol mixtures. Cars using pure ethanol, are not only using a renewable source, but are releasing fewer pollutants into the atmosphere, particularly carbon monoxide.

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