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Summary of chemical monitoring HSC chemistry

Transcript of chemistry HSC chemical monitoring summary

Chemical Monitoring and Management. Construct word and balanced formulae equations of all chemical reactions as they are encountered in this module: EQUATIONS to remember:

o Different products under different conditions: o Complete combustion: propane + oxygen carbon dioxide + water C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g) o Incomplete combustion: propane + oxygen carbon + carbon monoxide + water C3H8 (g) + 3O2 (g) C (s) + 2CO (g) + 4H2O (g) o Haber Process: o nitrogen + hydrogen ammonia + heat o N2 (g) + 3H2 (g) 2NH3 (g) H = -92 kJ/mol o Sulfate Content in Fertilizer: o barium chloride + sulfate barium sulfate + chloride 2o BaCl2 (aq) + SO4 (aq) BaSO4 (s) + 2Cl- (aq) o How Ozone Protects Us From UV Radiation: o Oxygen reacts with UV, forming 2 radicals: O2 + UV radiation 2O o Radical reacts with oxygen, forming ozone: O + O2 O3 o Ozone reacts with UV, forming oxygen and a radical: O3 + UV radiation O + O2 o Radical reacts with ozone, creating oxygen: O + O3 2O2 o All the CFC-Related Equations: o Formation of chlorine radical: CCl2F2 (g) + UV radiation Cl (g) + CClF2 (g) o Reaction of ozone: Cl (g) + O3 (g) ClO (g) + O2 (g) o Regeneration of chlorine: ClO (g) + O (g) Cl (g) + O2 (g) o Removal of chlorine radical: Cl (g) + CH4 (g) HCl (g) + CH3 (g) o Removal of chlorine monoxide radical: ClO (g) + NO2 (g) ClONO2 (g) o Formation of molecular chlorine: HCl (g) + ClONO2 (g) Cl2 (g) + HNO3 (g) o Decomposition of molecular chlorine: Cl2 (g) + UV radiation 2Cl (g) o The Heavy-Metal Sulfide Test: o The sulfide-test is based on the following equilibrium: S2- (aq) + 2H3O+ (aq) H2S (aq) + 2H2O (l) 1

1. Much of the work of chemists involves monitoring the reactants and products of reactions and managing reaction conditions:

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: Dr John Chapman: see assignment 1.2: Identify the need for collaboration between chemists as they collect and analyse data: As chemistry is such a broad field of knowledge, people tend to specialise within a particular branch, such as polymer chemistry or analytical chemistry. However, in real-life situations, many chemical problems require expertise and in depth knowledge from a wide range of chemical branches. Hence, collaboration between chemists is essential for solving chemical issues, or when dealing with large amounts of data being collected, as the chemists provide input and expertise from their own particular field, for a common goal. As chemists often work in teams, collaboration and communication is required to collectively benefit the team, as they collect and analyse information. o EG: An industrial process would require collaboration between physical chemists (for equilibrium considerations), organic chemists (for how the reaction occurs) and analytical chemists (for monitoring products). 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: Combustion: o Chemical reactions can form different products under different conditions. o Take, for example, the combustion of a simple hydrocarbon, propane. o In an environment with adequate amounts of oxygen, propane combusts completely, forming only carbon dioxide and water: propane + oxygen carbon dioxide + water C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g) o In an environment with insufficient oxygen, propane combusts incompletely, and can form a range of different products, such as carbon (soot), carbon monoxide, carbon dioxide and water. propane + oxygen carbon + carbon monoxide + water C3H8 (g) + 3O2 (g) C (s) + 2CO (g) + 4H2O (g) Monitoring: o Hence, under different conditions, chemical reactions can proceed in different ways, as seen by the combustion reaction above. o However, in certain situations (such as in car engines), only one reaction is desired. Thus, the reaction conditions must be monitored to ensure that only (or mostly) the wanted reaction occurs. o Carbon monoxide is a poisonous gas and can affect human health negatively. Carbon (soot) is carcinogenic to humans and can be irritating to the lungs. Both of these alternative products can also signal a decrease in fuel efficiency and result in a reduced energy yield from the fuel. 2

Products formed

Complete combustion Carbon dioxide and water

Relative ratio of oxygen to fuel

Unlimited (excess) oxygen available (high air to fuel ratio) Maximum energy Greenhouse gas, carbon dioxide, produced

Relative amount of energy released Environmental effects

Incomplete combustion Water and any combination of carbon monoxide, carbon (soot) and unburned hydrocarbons Insufficient oxygen for the amount of fuel. (low air to fuel ratio) Much less energy obtained from fuel. Much more polluting as CO is very toxic, hence, harmful to humans and animals. Carbon (soot) particles from the air are carcinogenic and irritating to the lungs. Other greenhouse gases may be produced.

1.4: Gather, process and present information from secondary sources about the work of practising scientists identifying:o the variety of chemical occupations: o a specific chemical occupation for a more detailed study: THE VARIETY OF CHEMICAL OCCUPATIONS: o The large range of jobs available in the chemical industry includes: Analytical chemistry. Bio-molecular chemistry. Colloid and surface science chemistry. Environmental chemistry. Industrial chemistry. Inorganic chemistry. Electrochemistry. Organic chemistry. Physical chemistry. Polymer chemistry . A SPECIFIC CHEMICAL OCCUPATION: o A summary of the job of an environmental chemist: Job includes reviewing operation of effluent water treatment systems and ensuring compliance with government environmental regulations. Reviewing industrys compliance with government environmental noise standards. Assessing levels of potential contamination in wastes (e.g. soil) intended for landfill disposal and classifying them in accordance with government guidelines. Managing disposal of contaminated wastes. Investigating reports of contamination in soil or groundwater to determine source and then arranging to correct it. Determining whether gas stack emissions contain unacceptable levels of regulated materials. Advising 3

engineers/managers of corrective actions needed if any of the above parameters show faults in systems. Answering public or professional enquiries or complaints regarding environmental performance. 2. Chemical processes in industry require monitoring and management to maximise production 2.1: identify and describe the industrial uses of ammonia Ammonia (NH3) is a colourless, toxic gas with a pungent odour The industrial uses of ammonia: o Solid and liquid fertilisers (through a reaction with sulfuric acid, nitric acid or phosphoric acid to form ammonium sulfate fertiliser, ammonium nitrate fertiliser or ammonium hydrogen phosphate fertiliser). The nitrogen in the ammonia is an essential plant nutrient. o Production of chemicals: Nitric acid (through the Ostwald Process) which in turn is used to manufacture synthetic fibres such as nylon and explosives such as TNT. Cyanide used in plastics manufacture and gold extraction o Cleaning agent: ammonia solution (ammonium hydroxide) destroys bacteria so it is a component of many household cleaners such as floor and bathroom cleaners. o Weak base: ammonia is used to safely neutralise acidic by-products in petroleum refining and in acid spills. Being a weak base, it generates heat slowly during neutralisation (an exothermic process) so does not cause further burning. o Manufacture of some pharmaceuticals (i.e. sulphonamides) and refrigerants. 2.2: identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen The synthesis of ammonia from hydrogen and nitrogen: o N2(g) + 3H2(g) 2NH3(g) For the synthesis of ammonia, nitrogen is obtained by fractional distillation of liquefied air and hydrogen is obtained by the reaction of steam with methane obtained from natural gas. o CH4(g) + 2H2O(g) H2(g) + CO(g) o The carbon monoxide gas can either be liquefied, reacted with a base (i.e. CaOH) or undergo the following reaction with water: o CO + H2O CO2 + H2

2.3: describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium TERMINOLOGY: o a reversible reaction is a reaction that can proceed in both directions o equilibrium is a reversible reaction proceeding in a closed system and with the rate of the forward reaction equal to the rate of the reverse reaction THE SYNTHESIS OF AMMONIA: o Hydrogen and nitrogen react very slowly to form ammonia, and at the same time, the ammonia decomposes into nitrogen and hydrogen. Thus, the reaction is reversible: nitrogen + hydrogen ammonia N2 (g) + 3H2 (g) 2NH3 (g) 4

o In a closed system, equilibrium will be reached when the rate of the forward reaction is the same as the rate of the reverse reaction. However, for this reaction the equilibrium is slow to be reached and lies to the left. o The synthesis of ammonia has a high activation energy because a lot of energy is needed to break the covalent bonds between the hydrogen molecules and the nitrogen molecules and form atoms that can rearrange to form ammonia. Nitrogen and hydrogen do not exist as single atoms; they both exist as diatomic molecules held together by strong covalent bonds. Nitrogen molecules are held together by very strong triple covalent bonds and the single covalent bond between hydrogen atoms is also quite strong. 2.4: identify the reaction of hydrogen with nitrogen as exothermic The reaction of hydrogen with nitrogen (Haber Process) can be represented as: o N2 (g) + 3H2 (g) 2NH3 (g) H = -92 kJ/mol From the equation we can see