9.2 Production of Materials summary

9.2.1 Fossil fuels

9.2.1.1 construct word and balanced formulae equations of chemical reactions as they are encountered

Three steps for writing equations: 1. Show all reactants and products in a word equation.

2. Write the correct formula for each reactant and product. 3.Balance the equation by placing coefficients in front of the formulas so that you have the same number total of each reactant element on each side.

9.2.1.2 Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum.

Ethylene is produced mainly from the cracking of by products in the refining of oil. Some large moleculed fractions can be passed over a heated catalyst that cracks the larger molecules into smaller molecules, this process is call cataylitic cracking.

9.2.1.3 Identify that ethylene, because of the high reactivity of it’s double bond is readily transformed into many useful products.

Ethylene’s double bond is very reactive and tends to break apart forming two single bonds with other objects (addition reactions). Some addition reactions it performs are Halogenation (reaction with halogen),hydrohalogenation (halogen + hydrogen), Hydrogen (h2), hydration (H2O).

9.2.1.4 Identify that ethylene serves as a monomer from which polymers are made.

Ethylene is polymerized to polyethylene CH2=CH2 -> (-CH2-CH2-)n. High pressures= soft, low density polyethylene (LDPE), tangled chains used in plastic bags. Low pressure produce harder high density HDPE, aligned chains heavy duty plastic bags.

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

Polyethylene is called an addition polymer as a small molecule (ethylene) adds together to from a much longer molecule (the polymer) and no other product.

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

LDPE (under high pressure) is formed using a peroxide containing an 0-0 bond that breaks easily forming free radicals which initiate the joining of ethylene monomers. HDPE (under low pressure) using catalyst made of transition metals and organometallic compounds which allow for more ordered orientation molecules to form long un branched and aligned molecules. Called the Ziegler- Natta process.

9.2.1.7 Identify the following as commercially significant monomers; vinyl chloride, styrene. By both their systematic and common names.

9.2.1.8 describe the uses of the polymers made from the above monomers in terms of their properties.

Monomer / Polymer
Common name / Sytematic name / Name / Properties / Used for
Ethylene / Ethene / LD polyethylene / Low density, soft / Flexible food bags
HD Polyethylene / High density, hard / Crinkly garbage bags
Vinyl chloride / Chloroethen / Polyvinylchloride (PVC) / Water resistant, flame resistant / Raincoats, shower curtains.
Styrene / Ethenylbenzene / polystyrene / Transparent dues to few crystals / Compact disc cases

9.2.2

9.2.2.1 discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry.

It is predicted that in the near future petroleum reserves will decrease so much that they will be uneconomical to use as widely as we do today fro power, transport etc. only 5% of worlds oil is used for plastics and only a small portion of these plastics are recycled therefore an alternative source of polymers will become economically viable and used in the future. Ethanol, cellulose etc.

9.2.2.2 Explain what is meant by a condensation polymer.

9.2.2.3 Describe the reaction involved when a condensation polymer is formed

A condensation polymer is formed by monomer molecules condensing out small molecules (such as water) as the polymer chain is formed. E.g.

9.2.2.4 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 flat, straight and rigid molecule formed by the condensation polymerization of glucose (maltose isomers).

The bulky CH2OH’s are on alternate sides of the maltose units making it very linear. Many of the hydroxyl groups form hydrogen bonds that hold the cellulose chains together making the fibres strong, yet the lack of free hydrogen makes it insoluble and resistant to chemical attack.

9.2.2.5 Identify that cellulose contains the basic carbon-carbon chain structures needed to build petrochemicals and discuss it’s potential as a raw material.
Each unit of glucose monomer in the cellulose chain consists of a 3 and 4 carbon chain. This is useful because these numbered chains if harvested separately could be used as a starting point to make many common polymers. Therefore this could be a renewable resource that has applications in a presently non renewable industry.

9.2.3

9.2.3.1 Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used.

9.2.3.2 describe the addition of water to ethylene resulting in the production of ethanol and identify the need for a catalyst in this process and the catalyst used.

Ethylene and ethanol are easily interchanged by addition of water (hydration) and removal of water (dehydration). Catalysts such as sulfuric acid, phosphoric acid, zeolites or heated ceramic solids can be used to catalyze both reactions.

9.2.3.3 describe and account for the many uses of ethanol as solvent for polar and non-polar substances.

Ethanol has both a non- polar CH3 end and a polar OH end. The non-polar end is therefore attracted to non- polar molecules such as hydrocarbons whilst the polar end is attracted to polar substances such as water. This enables ethanol to be used as a solvent in many applications as it will dissolve non- polar substances and take them away in a water solution.

9.2.3.4 Outline the use of ethanol as a fuel and explain why it can be called a renewable resource.

Ethanol can be used as a fuel because it readily combusts in air(oxygen) producing CO2 and H2O producing large amount of energy. It is almost always complete combustion due to its oxygen molecule. However it releases less energy per gram than as ethane because it is already oxidized. It is a renewable resource because it can be produced agriculturally although the cost in burning fossil fuels in the agricultural process can be high.

9.2.3.5 Describe conditions under which fermentation of sugars is promoted.

The conditions that promote the fermentation of sugar are;

·  A suitable micro organism such as yeast.

·  Water

·  A suitable temperature (warm but not hot)

·  Low oxygen concentrations favouring the fermenting yeast

·  A small amount of yeast nutrients such as phosphate salt.

Once the ethanol concentration reaches 14-15% the yeast cannot survive and the fermentation process stops, fractional distillation can be used to further concentrate ethanol.

9.2.3.6 Summarise the chemistry of the fermentation process.

Cane sugar waste, molasses which is rich in sucrose (C12H22O11) but uneconomic to separate. So water and yeast are added. The water reacts with sucrose to produce glucose and fructose, then the yeast ferments these to produce ethanol + carbon dioxide.

9.2.3.7 Define the molar heat of combustion of a compound and calculate the value for ethanol from first hand data.

The molar heat of combustion is defined as the energy released when 1 mole of the substance (fuel) undergoes complete combustion to form products in their standard states at 100kpa and 298k (1 atmosphere, 25degrees) using the formula ^H= -mC^T where m= mass of fuel, C is heat capacity of water 4.19 and ^t is change in temp.

Theoretically C2H5OH(l)+ O2(g) --à CO2(g) + H2O(l) ^H=-1360kj/mol ^Hcombustion= 1360kj/mol.

9.2.3.8 assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of it’s use.

Ethanol could be used in internal combustion engines if it is able to be economically produced from renewable resources or subsidized as a fuel to reduce air pollution.

Advantages;

·  Renewable resource

·  Reduce greenhouse gas emissions (if solar energy were used to distill it)

·  Easily transportable (liquid not gas but also highly volatile)

Disadvantages

·  Large areas of agricultural land would be needed to be dedicated to growing suitable crops with resulting problems.

·  Disposal of large amount of smelly waste producing in fermentation.

9.2.3.9 Identify the IUPAC nomenclature for straight chained alkanols from C1 to C8

No of C / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8
Prefix / Meth / Eth / Prop / But / Pent / Hex / Hept / Oct
Alcohol / Methanol / Ethanol / Propanol / Butanol / Pentanol / Hexanol / Heptanonl / Octanol

9.2.4

9.2.4.1 Explain the displacement of metals from solution in terms of transfer of electrons

A displacement reaction is where a metal converts the ion of another metal to the neutral atom. More active metals will displace less active metals from solution in a oxidation- reduction reaction. When a active metal is placed in a solution containing ions of a less active metal the more active metal losses one or more electrons and becomes a positive ion, these electrons transfer to the ions of the less active metal making them atoms. They switch places.

The solid is oxidized (losses electrons)

The ionesed metal is reduced (gains electrons)

9.2.4.2 Identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals.

The more reactive metal will displace a less active metal from a solution of it’s ions. The metals higher in reactivity loose electrons more easily (more easily oxidized).

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

For positive monatomic ions the oxidation state is the charge on the ion. E.g of iron in the sulfide FeS (Fe^2+ S^2-) is +2. A change in oxidation of these species corresponds to a loss or gain of electrons. E.g iron 2 to iron 3 Fe^2+ --àFe3+ +e-.

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

Redox reactions involve the transfer of electrons from one reactant to another. These are used in galvanic cells to generate electricity by having oxidation and reduction half reactions in different places by providing a wire between the two it generates an electric current. They can be made using two beakers, in acid, connected by a salt bridge.

9.2.4.5 outline the construction of galvanic cells and trace the direction of electron flow.

·  One electrode reaction liberates electrons which flow out of the metal of the electrode and into the external circuit.

·  These electrons flow through the metallic conductor of the external circuit to the other elements.

·  The reaction at the other electrodes consumers these electrons

·  Ions migrate through the solutions and connecting salt bridge to maintain neutrality.

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

·  Anode; is the electrode at which oxidation occurs.

·  Cathode: is the electrode at which reduction occurs

·  Electrode; the conductors of a cell which get connected to the external circuit.

·  Electrolyte; is the substance in which a solution or molten conducts electricity.

9.3.5

9.3.5.1 Distinguish between stable and radioactive isotopes and describe the condition s under which a nucleus is unstable.

An isotope (elements with different amounts of neutrons but same atomic number) is unstable (radioisotopes-undergo radioactive decay);

·  If its atomic number is greater than 83

·  If its ratio of neutrons to protons places it outside the zone of stability.

Half life is the time taken for half the radioactive material to half its radioactivity level.

Three types of radiation emitted;

·  Alpha- He^4>2 particle

·  Beta- 0e-1

·  Gamma- high frequency EMR

9.3.5.2 Describe how transuranic elements are produced

Transuranic element are man made elements with atomic numbers higher than 92(uranium) which are usually made from uranium isotopes. First few are made by bombardment of uranium with neutrons then that undergoing radioactive decay. The latter ones are made by bombardment of heavy nuclei with high speed positive particles such as helium or carbon nuclei, produced in particle accelerators. Beta and alpha decay.

9.3.5.3 Describe how commercial radioisotopes are produced

Most commercially produced radioisotopes are made in nuclear reactors as they are a good source of neutrons which bombard the atoms to form their isotopes.

9.3.5.4 Identify instruments and processes that can be used to detect radiation

·  Photographic film; darkens when exposed to radiation

·  Cloud chamber; supersaturated vapour of water or alcohol, when radiation passes through it ionizes some of the air which attracts droplets of liquid and shows the path of radiation, only clear for alpha

·  Geiger counter; measures the ionization of a gas (argon) produced from radiation. It measures the electrical pulse created by a cascade of ionized particles.

·  Scintillation counter; measure the flash of light emitted by certain substances when they are hit by radiation.

9.3.5.5 Identify the use of a named isotope in; industry and medicine.

Cobalt 60 is used in industrial radiography, to inspect metal parts and welds for defects.

Technetium-99m (Tc-99m) is used in a wide range of medical applications, such as pinpointing brain tumours and other locations of blood clotting in the body.

9.3.5.6 Describe the way in which the above name industrial and medical radioisotopes are used and explain their use in terms of their chemical properties

Cobalt 60; is used in inspecting metal parts and weld for defects. Radiation is directed at the are of interest from a sealed source of Co-60. Radiographic film is placed on the other side of the object and if there is a crack a greater amount of radiation will pass through that area and would be noticeable on the film. Co-60 is used because it is a gamma ray emitter and has a half life of 5.3 years so can be used in a chemically inert form.

Technetium-99m (Tc-99m); is used in many nuclear medicine procedures. It can be changed to a number of different oxidation states, enabling production of a wide range of biologically active chemicals which can be attached to a biological molecule that concentrates in the organ to be investigated.

It is used because of its; very short half life of 6 hours, emission of low energy gamma rays which are not harmful but can still pass through tissue, it is quickly eliminated from the body and it is reactive.