Chemical monitoring and mangagement summary9.4.2.1 identify and describe the industrial uses of ammoniaAmmonia is used to make solid and liquid fertilizers, explosives, nitric acid, sodium carbonate and some pharmaceuticals and household cleaners,. It is also used as a refridgerant.To make solid fertilized industrially, ammonia which is a weak base is reacted with sulfuric acid to form ammonium sulfate fertilizer and with nitric acid to form ammonium nitrate fertilizer.Identify that ammonia can be synthesized from its component gases nitrogen and hydrogen.Under pressure and heat nitrogen and hydrogen react in the ration of 3 volumes of nitrogen to 1 volume of hydrogen to produce 2 volumes of ammonia1 mol N + 3 mol H 2 mol NH3Describe the synthesis of ammonia occurs as a reversible reaction that will reach equilibriumThe synthesis of ammonia occurs as a reversible reaction. This means that ammonia is formed for n and h and once some is produce the reverse reaction happens. When n and h are initially added to the reaction vessel the reaction is slow. Equilibrium is reached whe the rate of the forward reaction = rate of the reverse reaction.To produce ammonia it needs to be shifted to the rightN2(g) + 3H2(g) 2NH3 (g)Identify the reaction of hydrogen with nitrogen as exothermicIn the forward reaction to produce ammonia it release 46kj of energy per mol NH3 formed.Explain why the rate of reaction is increased by higher temperaturesHigher temperatures will favour the left (endothermic) reaction make less ammonia but are need because at lower temperatures equilibrium would take years to establish and be impractical.Explain why the yield of the product in the haber process is reduced at higher temperaturesHigher temperatures would favour the reverse reaction by LCP because it is exothermic, thus producing less NH3 and more of the reactants.Explain why the haber process is base on a delicate balancing act involving reaction energy, reaction rate and equilibrium.As the temperature is increase more energy is available to exceed the reaction activation energy and thus the reaction rate between n and h to for nh3 increases. However increasing temperature favours decomposition of the ammonia product. A compromise temp providing a satisfactory reaction rate and satisfactory yield of ammonia is selected.

9.4.3.1 Deduce the ions present In a sample from the results of testsThe two types of ions are Cations (positive, have lost 1 or more electrons), attracted to cathode in electrolytic cell (electrolysis is reverse)Anions (negative, gain 1 or more electrons) attracted to anode.Ions are most commonly identified by precipitation reactions, however these may sometimes identify trace amounts of the ions in question.

A flow chart is often used to eliminate the multiple ions in search for one.9.4.3.2 Describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess it’s impact on scientific understanding of the effects of trace elements.AAS detects minute concentrations of an element in a sample solution by reading the unique absorption spectrum, that is related to an elements electron energy levels.

The flame containing the atomized sample absorbs light at the particular wavelengths characteristic to a particular elements in the flame and re emits in all directions. A detector records the intensity of light at each wavelength and a sharp drop in the intensity of a particular wavelength indicates the spectrum. The relative intensity and pattern of changes in intensity within each of the bands in the absorption spectrum indicate the concentration of the element in the test sample.

AAS has allowed for a great enhancement in the study of pollutants in the environment, being a extremely accurate way of detecting trace elements in a substance. Trace elements are needed in small amounts by living things and AAS has allowed many deficiencies etc to be found in some environments.

9.4.4.1 Describe the composition and layered structure of the atmosphere.The atmosphere is a 200-300km thick layer of gas surrounding the earth, with 75% of it’s mass below 15km, 99.997% below 90km. comprises mainly of nitrogen (78%), oxygen (21%) and argon (0.93%)It consists of two main layers; the troposphere and the stratosphere.Troposphere goes from the earths surface to 15km, the temperature drops with altitude in the troposphere. At the top is a region where the temp is relatively stable (tropopause; reduces the mixing of gases)The stratosphere is above the tropopause, in this temperatures rise with increasing altitude.9.4.4.2 Identify the main pollutants found in the lower atmosphere and their sources.

Main pollutants Main sources

Carbon monoxide Incomplete combustion in stoves, cars, fires and cigarettes.

Nitrogen oxides Combustion at high temperatures in vehicles and power stations.

Volatile organic compounds, such as hydrocarbons

Solvents and unburnt fuels.

Sulfur dioxide Some metal extraction processes and the burning of fossil fuels

Lead Leaded fuels, metal extraction, renovation old house containing leaded paints and electrical wire coverings

Particulates Incomplete combustion, earthmoving dust storms and some agricultural and industrial practices

9.4.4.3 Describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant.Ozone is an allotrope of oxygen with the formula O3. It is naturally in very small concentrations near the ground (0.02ppm) and is poisionous to humans and animal life, also being extremely reactive and capable of oxidizing many substances, making it a lower atmosphere pollutant. Large ozone concentrations make up photochemical smog.In the upper atmosphere however it forms a very thin ozone layer which filters out short wavelength UV light which is damaging to living tissue. 9.4.4.4 Describe the formation of a coordinate covalent bond.A coordinate covalent bond is one in which both of the shared electrons came from the one atom. In ozone, O2 is joined together normally and an unbonded pair of electrons from one of the O atoms breaks off and is shared with another O atom. Although this bond is produced differently it is still exactly the same.

9.4.4.5 Demonstrate the formation of coordinate covalent bonds using lewis electron dot structures ^^^^^^^^^^^^9.4.4.6 Compare the properties of oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding.Properties Gaseous oxygen Gaseous ozone ExplanationColour Colourless Blue -Boiling point -183 -111 The boiling point of

diatomic oxygen is lower than that of the ozone as diatomic oxygen has

lower molecular mass requiring less energy in the boiling process.

Solubility in water Sparingly soluble More soluble than oxygen

Non-polar O2 doesn not form strong intermolecular forces in the polar water. Ozone has a bent structure, which provides for some polarity of the molecule in it’s interaction with water

Chemical stability Far more stable than ozone

Far less stable than the oxygen molecule

Ozone is easily decomposed into oxygen molecules 2O3(g) 3O2(g)

Oxidation ability Less powerful oxidant

More powerful oxidant

e.g. reaction with metals; oxygen forms the oxide as the only product whereas ozone reacts more readily producing the metallic oxide and an oxygen molecule.

9.4.4.7 Compare the properties of the gaseous forms of oxygen and the oxygen free radical.Oxygen in its ground state has three pairs of electrons. When O2 is broken up it creates two oxygen free radicals each with two electron pairs and two unpaired electrons. The energy abosorbed in splitting the diatomic oxygen makes it very reactive.In order of reactivity O>O3>O2.9.4.4.8 Identify the origins of chlorofluorocarbons (CFC’s) and halons in the atmosphere.CFC were developed in the 1930’s to replace ammonia as a refrigerant. This was due to their properties being deemed safer than the explosive ammonia. Their inertness and low boiling point allowed them to be used as solvents propellants and blowing agents releasing the gases into the atmosphere.It was discovered that CFC did not react even react in the troposphere and made their way up to the stratosphere where uv energy broke the C-Cl bond and released Cl free radicals. These then react with ozone to deplete the ozone layer.Halons used In fire extinguishers underwent the same effect as CFC’s releasing even more reactive bromine free radicals, fortunately they were not used as much.

9.4.4.9 Identify and name examples of isomers (excluding geometrical and optical) of haloalkanes up to eight carbon atoms

9.4.4.10 Discuss the problems associated with the use of CFC’s and assess the effectiveness of the steps taken to alleviate these problems.CFC’s create problems of the depletion of the ozone layer, more UV radiation reaching earth (causing cancer), and an increase in the enhanced greenhouse effect.The can last for 150years depleting the ozone layer. Steps to reduce the formation of an ozone hole are: the montreal protocol; a treaty for the global reduction in CFCs, the identification and introduction of alternative chemicals such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), assistance to less developed countries to phase out CFC use.Global cooperation is needed to effective implement these steps.9.4.4.11 Analyse the information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained.Changes in atmospheric ozone concentrations where first noticed in the late 1970’s over the entire antartic. These measurements were take using UV spectrophotometers which were directed vertically upwards into the atmosphere. These spectrophotometers could also be directed vertically down and helium filled balloons used them. Later satellites were used to carry a total ozone mapping spectrophotometer (TOMS) which proved very efficient in recording changes in ozone levels.

9.4.59.4.5.1 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

AAS and gravimetric analysis are the most common way s of determining the concentration of ions in the water are within world health standards.Total dissolved solids (TDS)TDS are determined by evaporation to dryness of a known volume of a filtered sample. The value is converted to ppm and expressed in mass per volume units. If the solids are ionic there amount can be determined by a conductivity probe and data logger.HardnessHardness is due to the presence of calcium and magnesium ions in the water. These form insoluble compounds with soap ions and produce scum stopping the soap from lathering. Hardness is tested by precipitating the calcium and magnesium ions from a known volume of water sample with a solution of sodium carbonate (of known concentration) followed by filtering and drying of the precipitate. Most of the insoluble salt is assumed to be calcium and the concentration of calcium ions is calculated and reported in ppm.AcidityA ph reading below 7 would be expected where there are acid sulfate soils or where there is acid produced by decomposition of organic matter in stagnant situations. The test can be conducted with a data logger and pH probe, universal indicator solution or paper or pH meter. Dissolved oxygenThere are several test for determining the DO in a water sample. The winkler method fixes the amount of dissolved oxygen, which is later determined by titration.The amount of manganese dioxide produce by adding manganese (II) ions and hydroxide ions is a measure of DO. Acified iodide ions are added to cause the manganese dioxide to produce a yellow iodine solution. This is then titrated against a standard sodium thiosulfate solution using starch as the indicator. The indicator turns a blus colour with the iodine and the blue disappears at the endpoint. To conduct the test no aid is to be trapped with the sample and it is to be kept in the dark to reduce algae photosynthesis increasing the DO.Biochemical oxygen demand (BOD)BOD measures the amount of oxygen used by bacteria and other micro-organisms during a five-day period. The sample bottles are held below the water surface and away from the bank. One sample is measured for DO as soon as possible while the other sample is kept in a dark place for 5 days then tested for DO. The difference between the two is the reading give as milligrams per litre.9.4.5.2 Identify factors that affect the concentration of a range of ions in solution in natural bodies of water such as rivers and oceans.Factors include:

- The frequency of the rainfull (i.e. floods and droughts)- Water temperatures- Evaporation rates- Soil type- Pollution sources, such as the presence of animal faeces and gertiliser usage

(leading to eutrophication)- Land use

Removal of vegetation due to farming and development practice increase the amount of salt in the water table an thus in the rivers.

Earthmoving on waterside developments can expose layers containing sulfide to air, oxidizing them and producing sulfuric acid which can kill fish etc.High evaporation rate sin the dead sea have increased salt concentrationRun off water containing phosphate and other ions, affecting the growth of organisms.9.4.5.3 Describe and assess the effectiveness of methods used to purify and sanitise mass water supplies. Most purification methods are variations of the following processFlocculation and sedimentation filtration sanitization pH adjustment

- Large solids are collected in grates- Coagulants such as iron(III) chloride are added to neutralize the surface charges

of the suspended particles allowing them to precipitate out. - Sand filtration is used and membrane filters for smaller particles. - Chlorine gas Cl2, liquid sodium hypochlorite solution NaOCl (aq) or solid

calcium hypochlorite Ca(OCl)2 are used as disinfectants. They are needed to ensure the completely remove harmful bacteria such as cryptosporidium and giardia.

- Constant assessment of the effectiveness of these methods is needed with testing and public health surveys.

9.4.5.4 Describe the design and composition of microscopic membrane filters and explain how they purify contaminated water.These filters have microscopic pores which can reduce or stop the need to chemically treat the water. They come as microfiltration, ultrafiltration, nanofiltration or reverse osmosis membranes depending on the size of the pore.The membrane is made from synthetic polymers in a mixture of solvents.Semi permeable membranes used in reverse osmosis are either made of cellulose acetate or a layer of polyamide attached to another polymer. Under pressure these allow passage of water molecules but not most atoms, ions or molecules.Water is made to flow across the membrane not through it. This reduces blockage.