1.1 Outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist and explaining the chemical principle that the chemist uses
Collaboration is the sharing of findings, information and research methods between scientists in different subdisciplines. This is important among chemists because:
- Different chemists specialise in different fields (e.g. procedures, chemical concepts) and hence some problems are better solved with the assistance of specialist chemists
- It reduces the workload, and thus increases efficiency
- The communication of ideas to share knowledge allows for the advancement of research
- Reliability (repetitions of similar experiments) and validity (ensuring data measured is accurate and relevant to desired aim) are strengthened by peer critiquing
1.3 Describe an example of a chemical reaction such as combustion, where reactants form different products under different conditions and thus would need monitoring
Need for Monitoring Combustion Reactions
- In combustion, fuel-to-oxgyen ratios must be monitored to maximise energy output and efficiency and minimise harmful pollutants:
o A plentiful supply of oxygen should be available for complete combustion to occur – the more complete the combustion, the more CO2 is produced and so more high-energy C=O bonds are formed to release more energy.
Eg. Complete combustion of methane: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
- Otherwise, if there is insufficient oxygen, incomplete combustion takes place, forming undesirable products such as, carbon monoxide (poisonous) and soot (lung-irritant and carcinogenic), which are harmful to human health.
Eg. Incomplete combustion of methane: CH4(g) + 5/2O2(g) → CO(g) + 2H2O(g) AND CH4(g) + O2(g) → C (s) + 2H2O(g)
- CO2 emission must be monitored, so that knowledge about its effect on the enhanced greenhouse effect can be determined and data used for control strategies.
1.4 Gather, process and present information from secondary sources about the work of practising scientists identifying: - the variety of chemical occupations - a specific chemical occupation for a more detailed study
- Ammonia is used industrially as a feedstock for the manufacture of:
o Solid and liquid fertilisers: NH3 (g) + HNO3 (aq) → NH4NO3 (aq) OR NH3 (g) + H2SO4 (aq) → (NH4)2SO4 (aq)
- Nitric acid used to make gunpowder/explosives (TNT; trinitrotoluene): NH3 (g) + 2O2 (g) → HNO3 (g) + H2O (l)
- Hydrogen. Obtained by the reaction of methane with steam in the presence of a nickel catalyst at 750°C:
|750°C, nickel catalyst|
|CH4(g) + 2H2O(g) →||H2(g) + CO(g)|
2.3 Describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium (PLUS) 2.4 Identify the reaction of hydrogen with nitrogen as exothermic
The synthesis of ammonia occurs as a reversible reaction that will reach equilibrium:
N2(g) + 3H2(g) 2NH3(g); ∆H = -92 kJmol-1
- At standard conditions, the equilibrium lies well to the left, so there is a very low yield of NH3. However, the reaction conditions established in the Haber process make it commercially viable.
- The forward reaction is exothermic (releases heat to the surroundings) as denoted by the negative ∆H.
2.5 Explain why the rate of reaction is increased by higher temperatures (PLUS) 2.6 Explain why the yield of product in the Haber process is reduced at higher temperatures using Le Chatelier’s principle (PLUS) 2.9 Analyse the impact of increased pressure on the system involved in the Haber process
2.7 Explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium
- The optimal conditions for the manufacture of ammonia are a compromise between reaction rate, yield and economic factors. ie. a balance between conditions that optimise yield, rate and cost:
2.8 Explain that the use of a catalyst will lower the reaction temperature required and identify the catalyst(s) used in the Haber process
2.10 Explain why monitoring of the reaction vessel used in the Haber process is crucial and discuss the monitoring required
2.11 … Describe the conditions under which Haber developed the industrial synthesis of ammonia and evaluate its significance at that time in world history
- Haber developed a method of producing ammonia.
- The production involved reacting hydrogen gas with nitrogen gas at high temperature (400-500°C) and high pressure (-300 atmospheres) with a magnetite (Fe3O4) catalyst.
- Prior to his discovery the world relied on obtaining ammonia from natural sources such as guano, (mostly from Chile).
- Haber’s discovery in 1908:
o Provided Germany a reliable synthetic source of ammonia to make fertiliser for crops, needed to feed their large
o Ended reliance on imports of depleting natural sources of ammonia from distant countries (eg. Chile).
o Provided Germany with a reliable source of ammonia to produce nitric acid used to make explosives, which facilitated
Germany’s preparation for World War 1. Without a reliable source Germany would not have been able to wage war. o Insulated Germany during the Naval blockade whereby Germany was surrounded by naval ships to block imports and were cut off by Chile, an ally of England, of their guano supply. This allowed Germany continue to produce explosives
without the reliance on Chile imports, thus prolonging the war and indirectly causing the loss of many more lives.
o Led to the over-use of fertiliser by farmers. The resulting run-off contaminates a river, causing toxic algal blooms which reduce dissolved oxygen levels.
- Therefore his discovery was very significant at that time in world history.
- When identifying one cation present in a solution, use a new sample for each test.
- When analysing mixtures with several cations:
o An excess reagent is added until no further precipitate forms.
- The precipitate is separated from the filtrate (to eliminate interference) using filtration or a centrifuge (quicker) before performing the next test.
- A centrifuge spins test tubes at high speeds and flings the precipitate to the bottom.
- Sufficient nitric acid ensures all CO32- is destroyed and does not interfere with other tests.
- All carbonates react with dilute acids to form gas
3.2 Describe the use of atomic absorption spectroscopy in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of trace elements
3.3 Perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions Cations: Barium, calcium, lead, copper and iron, Anions: Phosphate, sulfate, carbonate and chloride
- A flame test is used to distinguish some cations by the colour their salts impart to a flame.
- The flame decomposes the ionic compound into its cations and anions, and it is the cations that give the distinctive flame colours:
- Dip a platinum or nichrome wire into a small beaker of concentrated HCI. Heat it strongly in the flame to sterilize it.
- Moisten the wire in the acid and dip the wire into a solid sample of the metal compound.
- Place the wire on the edge of the flame and observe the colour using a colourless Bunsen burner flame (open air hole).
- Repeat for each metal (Ba, Ca, Cu)
Note: Another method is dissolving chloride salts in water and spraying into a Bunsen flame using an atomiser.
3.5 Identify data, plan and select equipment and perform first-hand investigations to measure the sulfate content of lawn fertiliser and explain the chemistry involved:
3.6 Analyse information to evaluate the reliability of the results of the above investigation and to propose solutions to problems encountered in the procedure
Main Problems Encountered and How it was Solved
- Ensuring no CO32- is present. CO32- may precipitate with Ba2+ so HCl was added to acidify the solution and remove any carbonate ions that could be present, prevent the precipitation of barium salts with CO32-.
- Ensuring complete precipitation of SO42–. The complete precipitation of sulfate was ensured by adding excess BaCl2.
- Filtering the very fine BaSO4 precipitate. This was overcome by:
- Digesting solution by heating near boiling point which increase the solubility of the precipitate at equilibrium and reduce relative supersaturation, thus aiding the coagulation of the ppt.
- Constant stirring during slow addition of precipitating agent, which prevents sudden supersaturation and subsequent immediate precipitation, thus aiding the coagulation of the ppt.
- Adding agar-agar solution, which offers a surface on which the ppt can be adsorbed, so that the precipitate is coagulated.
- Ensuring the BaSO4 is free of water, Cl ions etc. Adding agar-agar solution and excess would contribute to the final mass. This was prevented by undertaking many rinsings when transferring the solution the filter funnel (quantitative transfer), washed precipitate with distilled water to remove chloride ions, placing the precipitate in an oven and drying to constant mass.
Further Solutions to Problems Encountered
- Use excess precipitating reagent to ensure all SO4– is precipitated.
- Use a sintered glass filter (sintering glass crucible under vacuum) instead of fine filter paper, which is of bigger pore size. Its very small pore size prevent very fine particles passing through as part of the filtrate. This would mean that agar-agar solution would not be needed, thus increasing validity.
- Use acetone for the final rinsing to remove water.
- Use a greater mass of solid, so that weight of collected is greater, reducing the % error.
- Use a more accurate electronic balance that measures up to at least 5 significant figures.
3.4 Gather, process and present information to describe and explain evidence for the need to monitor levels one of the above ions in substances used in society
Need to Monitor Lead Ions Used in Society
- It affects the central nervous system (primarily the brain) to cause intellectual impairment in young children (e.g. decreased concentration span), neurological disorders & possibly brain damage, if unchecked.
- Lead has many routes of entry into the body: ingestion, inhalation and absorption by the skin.
- Lead also causes anaemia (by inhibiting haemoglobin formation and thus the availability of oxygen to body tissue).
- It is a cumulative poison (bio-accumulates) because it builds up in bones and it is difficult to excrete.
- Sources of lead are widespread. Examples include:
- Released into the atmosphere from leaded petrol. Monitoring of soils near major roads is required to ensure that people around these areas are not exposed to excessive concentrations.
o From lead compounds in paints. Hazards occur when paint layers from older homes are stripped away.
- Mining and refining, e.g. Mt Isa – risk to children. Car battery manufacture and disposal.
- So, because lead is dangerous and widespread, its monitoring is essential in areas of heavy traffic, areas providing drinking water and food and areas producing and using lead.
3.7 Gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control
Effectiveness of AAS in Pollution control
- Atomic absorption spectroscopy (AAS) is an important technique in measuring the concentrations of metal ions in very minute quantities. A liquid sample containing the lead ion is aspirated through a tube into a flame hot enough to vaporise the sample into atoms. A cathode lamp transmits light with the desired frequency through the atomised sample. A detector measures the amount passing through the flame and gives out the absorbance (amount absorbed) reading.
- The basis of AAS is the result of the electron structure of the analysed atom. Electrons move to higher energy levels by absorbing electromagnetic radiation of a specific frequency. Since lead has a unique set of electron energy levels, it absorbs the radiation with a specific frequency. The greater the concentration of the lead ion, the more radiation is absorbed and the less reaches the detector. The amount of light absorbed is proportional to the amount of lead present (according to the Beer-Lambert Law). A calibration (standard) graph using solutions of known concentrations allows the concentration of the unknown to be determined.
- Even very low blood levels of lead are a cause for concern. (10 mg/dL or above-however, lead can impair normal development even below 10 mg/dL).
- AAS is sensitive enough to be able to detect levels at these orders of magnitude (of ppm/ppb).
- AAS analysis has many other advantages:
o lts ease of operation and reliability/precision
- It is quick, as sample is simply aspirated into the atomiser and analysed wrt standards.
- It is relatively cheap to operate.
- It is a more accurate method than the use of gravimetric/volumetric analyses & colorimetry
- Its high degree of freedom from interference & its specificity. No two elements absorb at the same wavelength-the presence of another element does not directly interfere with the absorption of radiation by lead.
- The ability of the atom to absorb is independent of atomiser temperature so there is no interference from temperature.
- Many lead samples can be analysed quickly (to assist with reliability).
- Minimal contact with toxic lead (compare with gravimetric analysis).
- There are some disadvantages.
- Daily calibration with the lead ion is required for the machine to measure accurately.
- At high concentrations Beer-Lambert’s law (absorption is directly proportional to concentration) fails and precision can be compromised.
- Another problem in atomic absorption is that it is very useful for analysing liquid samples, but has not been successfully used for the direct analysis of solids or gases (the difficulty arises in the atomizer stage).
- Even though the actual AAS measurements are accurate and precise, error can occur at the dilution stage when standards are prepared.
- AAS is an easy and reliable method for determining lead concentrations once standards are prepared carefully. Many samples and effective dilutions can ensure that the linear portion of the Absorbance versus Concentration standard curve is used. Solid and air samples can still be analysed via acid digestion/making solutions so AAS sensitivity, specificity and safe ease of operation are ideal factors for analysing lead which at even low levels can be dangerous.
Trophosphere, temperature & stratospheric pollution
- Temperature differences cause differences in the density of air.
- Less dense air at low altitudes
- Less dense air rises & denser air (top) sinks to allow for vertical mixing ie.
- Convection currents allow for effective vertical mixing
- The continual mixing means that stable substances such as CFCs and halons can eventually pass the tropopause/enter the stratosphere where they can be photo-dissociated (by high-energy UV radiation) to produce radicals which can damage ozone.
4.3 Describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant
Ozone as an Upper Atmosphere UV Radiation Shield
- Ozone in the stratosphere, in the form of an ozone layer, protects us from harmful ultraviolet radiation (UV light):
- The ozone-layer blocks the harmful UV-B and UV-C rays (can cause cancer and severe sunburn) from passing through the atmosphere. The useful UV-A (needed for photosynthesis) can still pass through.
- The following equations show how ozone is formed and destroyed as well as how it protects us from harmful UV radiation:
- Every time an oxygen/ozone reacts with UV light, it absorbs it, thus acting as a UV radiation shield.
Ozone as a Lower Atmosphere Pollutant
- However, when ozone is found in the lower atmosphere (troposphere), it is considered a serious pollutant. Ozone makes up the most hazardous component of photochemical smog. Sunlight splits nitrogen dioxide and the free radical produced joins with oxygen to form ozone.
- Detrimental consequences of high ozone levels in the troposphere include:
o Damages forests and crops. High concentrations cause plants to close their stomata. This slows down photosynthesis and plant growth. Ozone may also enter the plants through the stomata and directly damage internal cells.
o Destroys nylon, rubber, paints and other materials.
o Induce and aggravates respiratory ailments by injuring/destroying living tissue (eg. alveoli, bronchioles).
- Produces headaches and premature fatigue.
4.4 Describe the formation of a coordinate covalent bond (PLUS) 4.5 Demonstrate the formation of coordinate covalent bonds using Lewis electron-dot structures
4.9 Identify and name examples of isomers (excluding geometrical and optical) of haloalkanes up to eight carbon atoms
- Isomers are compounds with same chemical formula but different structural formula.
- Haloalkanes are organic compounds formed when one of the hydrogens of an alkane is replaced by a halogen atom (F, Cl, Br or I).
- Count the number carbons in the longest carbon chain. In this case, the parent alkane is propane.
- Identify, name and number the halogens, using ‘fluoro-’, ‘chloro-’, ‘bromo-’ and ‘iodo-’ as prefixes and the di-, tri-, and tetra-as pre-prefixes. In this case, we take the left-most carbon as C1, so there are 3 chlorines (2 on C1 and 1 on C3), and there are 3 fluorines (1 on C1 and 2 on C3). Therefore, the prefixies are: 1,1,3-trichloro- and 1,3,3-trifluoro.
- Place the halogens prefixes in alphabetical order and the name of the parent alkane at the end: 1,1,3-trichloro-1,3,3-trifluoropropane
- Ensure the numbering of the lowest possible locant. Say instead we took the right-most carbon as C1: 1,3,3-trichloro-1,1,3-trifluoropropane. In this case, both names have an equal sum. If this occurs, give the lower numbers to the more electronegative halogen (F > Cl > Br > I). Thus, the correct name is 1,3,3-trichloro-1,1,3-trifluoropropane.
- Draw the structural formula of FOUR isomers of C4H7ClF2 and identify their IUPAC name:
4.8 Identify the origins of chlorofluorocarbons (CFCs) and halons in the atmosphere (PLUS) 4.10 Discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems (PLUS) 4.12 Present information from secondary sources to write the equations to show reactions involving CFCs and ozone to demonstrate the removal of ozone from the atmosphere
CFCs – Their Origin and Problems associated with their Use
- CFCs were used as:
o Refrigerants in fridges and air-conditioners (as a replacement for NH3; due to boiling points being as little as 0oC) o Propellants in aerosol spray cans.
o Foaming agents in the manufacture of foam plastics like polystyrene. o Solvents in electronic circuits.
- They were used because they are odourless, non-toxic and non-flammable. They are also unreactive and thus do not breakdown or react in the troposphere. Therefore, they can slowly diffuse into stratsosphere, where they can encounter high-energy UV radiation which photo dissociates them into radicals including monatomic Cl. The products of UV decay of CFCs catalyze the destruction of ozone. The equations below represent the depletion of ozone in the stratosphere due to presence of CFCs:
- It is evident that the Cl radicals are recycled to destroy thousands of ozone molecule in a catalytic way ( Cl is continually reformed). Thus one CFC molecule can lead to the destruction of thousands of O3 molecules which are important in the stratosphere for filtering out harmful UV-B (and some UV-C) radiation.
Harmful Effects of UV Radiation
- UV can damage DNA, killing the cell or making it unable to replicate properly. This can cause permanent damage to skin tissue, forming skin cancer.
- An increase in respiratory conditions including asthma and a reduction in lung function.
- Suppression of the immune response system.
- Adverse effects on the eyes, damaging the retina and forming cataracts (cloudiness) of the lens.
- High levels destroy biological molecules such as nucleic acids (RNA and DNA) and protein.
- Affects aquatic organisms (e.g. plankton, fish, shrimp and crabs), decreasing their reproductive capacity and impairing larval development.
- Decreases yield of sensitive plants (e.g. soybeans and rice) since it affects photosynthesis.
- Contributes to the formation of photochemical smog.
- Breaks down polymers and paints faster. Polymers become more brittle with UV exposure. (Inorganic substances such as titanium dioxide can be added to absorb UV radiation and protect the polymer.)
Strategie(s) taken to Alleviate Ozone Depletion – The Montreal Protocol
- The Montreal Protocol (1987) is an international treaty to protect the ozone layer by phasing out ozone-depleting chemicals,
such as CFCs and halons, and replacing them with less-damaging molecules.
o It required the phasing out of ozone-depleting chemicals according to a timetable, with different phasing out periods for developed and developing countries. Developed countries provide financial assistance to help developing countries to
phase out CFCs.
o It provides incentives and trade sanctions to ensure its targets are achieved.
o Australia is well ahead in phasing out the use of ozone-depleting chemicals – CFCs, HCFCs, halons and tetrachloromethane are all phased out.
- The Montreal Protocol has been successful as progress in reducing emissions of CFCs worldwide appears to be quite significant, and most countries are meeting the required targets. This has been largely due to the availability of acceptable alternative compounds such as HFCs to replace CFCs.
- Overall, reduction in atmospheric concentrations of CFCs has not been major, but ozone thinning has not become worse.
Strategie(s) taken to Alleviate Increased UV Radiation
- The CFCs already in the stratosphere cannot be removed so measures are needed to reduce the effects of problems caused by CFCs (e.g. high levels of UV radiation).
- These include using sunscreens with high sun protection ratings (at least SPF 30+) and the use of UV stabilisers in polymers to reduce breakdown by UV radiation.
4.14 Present information from secondary sources to identify alternative chemicals used to replace CFCs and evaluate the effectiveness of their use as a replacement for CFCs
HCFCs · They are only moderately effective in minimising ozone depletion:
- HCFCs are broken down in the troposphere due to the high reactivity of their bonds, which are susceptible to attack by reactive radicals and atoms.
o Only a small % of HCFCs reach the stratosphere, but once they do, ozone destruction rapidly occurs.
- Hence their ozone depletion potential, although significant, is much less than that of CFCs. Their long-term toxicity to humans is yet to be determined.
o HCFCs replaced CFCs in refrigeration and as foaming agents, but they were only a temporary solution.
HFCs · These widely used as replacements for CFCs and HCFCs. They are very effective in minimising ozone depletion:
- HFCs contain reactive C-H bonds (so they degrade in the troposphere) and have no chlorine (so they do not form radicals and hence have no ozone depletion potential).
o The most widely used HFC is HFC-134a, which is used in refrigeration and air conditioning.
- While HFC-134a is non-flammable and has suitable properties, it is more expensive and less efficient than the CFCs it replaces, but this is a small price to pay for protecting stratospheric ozone.
Judge- Neither alternative class of chemicals for ozone replacement has been totally successful, but HFCs have been shown to ment be very promising so far. Further research is still required to develop effective alternative chemicals to CFCs
4.11 Analyse the information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained
Information Indicating Changes in Ozone Concentrations
- Measurements of the total amount of ozone in a column of atmosphere have been recorded since 1957.
- Global Ozone Depletion: Globally, in recent years there has been a 3 to 8% in the amount of ozone in the atmosphere on an averaged year-round basis.
- However, the main depletion of ozone has occurred over the Antarctic.
The Antarctic Spring Ozone Hole
- There is a serious periodic depletion of the ozone-layer that occurs every spring over Antarctica; it is called the ‘Ozone Hole’.
- This is due to the conditions of Antarctica in winter, as well as spring.
- Antarctic winters are perpetually dark; the cold conditions, as well as solid particulate catalysts in the air, encourage the
following reaction to occur:
HCl (g) + ClONO2 (g) → Cl2 (g) + HNO3 (g)
- This has zero effect on ozone levels during the winter. However during early spring, the situation changes dramatically: Cl2 (g) + UV radiation → 2Cl⦁ (g)
- Hence in spring, there is another source of chlorine radicals to destroy more ozone. This reduces the concentration of ozone dramatically, causing a hole.
- Eventually, the fixed amount of Cl2 created over the winter is blown away by Antarctic winds and the ozone layer slowly regenerates.
Changes Observed in Atmospheric Ozone Concentrations:
- The changes observed have been in global ozone concentrations, demonstrating a significant depletion in ozone concentrations of about 3 to 8% in recent years. However, more significantly, there has been dramatic ozone depletion over the Antarctic in Spring of about 50 to 90%.
4.13 Gather, process and present information from secondary sources including simulations, molecular modelling kits or pictorial representations to model isomers of haloalkanes
5.1 Identify that water quality can be determined by considering: concentrations of common ions, total dissolved solids, hardness, turbidity, acidity, dissolved oxygen and biochemical oxygen demand
Concentration of Common Ions:
Common ions that determine water quality include:
- Cations: Barium, calcium, lead, copper and iron. Very quickly and easily measured using spectroscopic methods eg. AAS
- Anions: Phosphate, sulfate, carbonate and chloride. Measured through gravimetric analysis. eg. Cl– precipitated and weighed as silver chloride.
5.2 Identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers and oceans
5.3 Describe and assess the effectiveness of methods used to purify and sanitise mass water supplies
5.4 Describe the design and composition of microscopic membrane filters and explain how they purify contaminated water
5.5 Perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples
- Water samples were collected from:
- Coonong Creek – Forest Road / Hunter street, Kirraweee
- Saville Creek – North West Arm Road, Gymea
5.6 Gather, process and present information on the range and chemistry of the tests used to: identify heavy metal pollution of water, monitor possible eutrophication of waterways
5.7 Gather, process and present information on the features of the local town water supply in terms of: - catchment area - possible sources of contamination in this catchment - chemical tests available to determine levels and types of contaminants - physical and chemical processes used to purify water - chemical additives in the water and the reasons for the presence of these additives
- A catchment is an area where water is collected by the natural landscape. In a catchment, all rain and run-off water eventually flows to a creek, river, lake or ocean, or into the groundwater system
- Warragamba Dam is Sydney’s main water storage dam, and one of the largest domestic water supply dams in the world.
- The dam lies on the Warragamba River, for which it is named.
- Catchment areas are areas of land from which rain water drains toward a common water-body.
Chemical and Physical Purification Process
- Screening (physical) – metal sieve/grate traps removes large debris
- Flocculation (physical) – flocculating agent (eg. FeCl3/Al(OH)3) is added followed by stirring to encourage flocculation and precipitate formation. suspended matter to allowed to settle.
- Sand filtration (physical) – unsettled precipitate, absorbed impurities and odours are removed by filtering it through layers of sand and gravel.
- Chlorination (chemical) – Chlorine adds to disinfect the water of pathogens including bacteria and some viruses.
- Further treatment if necessary or desired
- Chlorine (Cl2) is added to the water supply (by bubble contact) as a disinfecting agent. Hypochlorite ions (OCl–) are formed, which kill bacteria and some viruses: Cl2 + H2O ⇌ HClO + H+ + Cl–
- Fluoride (F–) is added in the form of NaF at 1ppm to the water to strengthen tooth enamel in growing children.
- Ca(OH)2 is added to pH adjustments to prevent corrosion of pipes.