11. Air and Water. The composition of air is as follows: The fractional distillation of liquid air. The process has 2 fundamental stages:

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1 The composition of air is as follows: The fractional distillation of liquid air The process has 2 fundamental stages: 1. Air is cooled to a very low temperature so that most of its components liquefy.

2 2. The liquid air is allowed to warm up slowly and its constituents are collected according to their boiling point (see p212). NB. Dust, carbon dioxide and water are removed at the beginning of the process. Why? Give uses of the following: Oxygen: Nitrogen: Noble Gases: CC p213 Q1

3 Pollution The main pollutants in the Earth s atmosphere: Carbon dioxide Carbon monoxide Sulphur dioxide Nitrogen oxides Ozone Lead compounds and particulates 1. Carbon dioxide Technically, not a pollutant, it is produced by the complete combustion of fossil fuels (or fuels that contain carbon), by respiration and by the reaction of acids with carbonates. eg. Methane eg2. Petrol EQN Is the reaction exothermic or endothermic? This gas is considered to be the main culprit of GLOBAL WARMING - it is a greenhouse gas

4 The greenhouse effect: The main greenhouse gases are: 1. methane 2. water vapour 3. carbon dioxide. The diagram shows how the greenhouse effect works.! Greenhouse effect 1. Electromagnetic radiation at most wavelengths from the Sun passes through the Earth s atmosphere. 2. The Earth absorbs electromagnetic radiation with short wavelengths and so warms up. Heat is radiated from the Earth as longer wavelength infrared radiation. 3. Some of this infrared radiation is absorbed by greenhouse gases in the atmosphere. 4. The atmosphere warms up.

5 2. Carbon Monoxide Fuels that contain carbon will produce this gas when they are burnt in insufficient oxygen: They may also produce soot... Both are examples of INCOMPLETE COMBUSTION. Effects: Carbon monoxide is a colourless, odourless, deadly gas due to the fact that its binds with haemoglobin in the blood, causing oxygen starvation. Write 3 equations for the combustion of butane:

6 3. Sulphur dioxide Fossil fuel contain sulphur which forms this acidic, pungent gas when burnt... The gas combines with water to form the strong acid, sulphurous acid... Effects: This gas is the main cause of acid rain, which attacks buildings and affects ecosystems (rivers, plants, insects,...). It also irritates the eyes and causes respiratory problems. 4. Nitrogen oxides Burning fossil fuel in engines causes the formation of a mixture of nitrogen oxides. Effects: Acid rain and respiratory problems. 5. Ozone Can be formed in car engines and in the upper atmosphere. Effects: In the stratosphere, the ozone protects life on earth from the harmful high energy radiation from the sun. NB. The use of CFCs (chlorofluorocarbons) has been banned, as they can cause this layer to be depleted, as they break down the ozone into oxygen. At ground level, ozone can lead to respiratory problems.

7 6. Lead compounds and particulates Lead used to be added to fuel to improve efficiency, but was banned due to the damage caused to children s brains and adults kidneys and nervous systems. Particulates, mainly soot, are the tiny particles that are the product of incomplete combustion of fuels. Reducing pollution In order to reduce the effects described above, we can: 1. Reduce carbon dioxide emissions (more efficient engines, public transport, save energy in the home, use alternative or sustainable sources of energy,...) 2. Treat waste gases in industry in order to prevent the harmful gases getting into the atmosphere. Power stations have flue gas desulphurisation - sulphur dioxide is reacted with calcium hydroxide (see CC p241 for details). 3. Control lead emissions and ban the use of lead in petrol. 4. Remove sulphur from fuels before they are burnt. 5. Use catalytic converters in cars and other vehicles: CC p215 Q2, 3 and 4

8 Water Uses of water: In the home Farms Industry Power stations How is water purified? When we take water from relatively clean sources (rivers, reservoirs, aquifers,...) and make it fit for human consumption, we must remove: Particles (large and microscopic) Microbes - bacteria and tiny organisms The process - a typical water treatment plant...

9 Notes: Water may not be disinfected (chlorinated) if it is destined for uses other than human consumption (eg. golf courses) Fluoride can be added to reduce tooth decay in the population Tests for water Physical test - pure water boils at ºC and freezes at ºC Chemical tests - water or an aqueous solution will cause the following colour changes: I. Anhydrous copper(ii)sulphate will turn from white to blue... II. Anhydrous cobalt(ii)chloride will turn from blue to pink

10 Rust and Rust prevention Corrosion: when a metal is attacked and eaten away by another substance, such as an acid or water. Oxidation is taking place: Rusting is the oxidation of iron and alloys of iron. It is a complex process that can be summarised as: Preventing rusting For rusting to happen, we both WATER and OXYGEN must be present. To prevent rusting, we must stop the iron coming into contact with one or both of these. The two general methods: COATING or CHEMICAL Coating A layer or coat prevents attack from water or oxygen. This can be achieved by using: Paint (bridges, boats, bicycles,...) Grease and oil (machines, chains,...these also lubricate) Plastic (garden chairs, fences, wires,...) Tin (food containers - can be deposited using electrolysis and is non toxic) Chromium (cars, motorcycles,... - can be deposited using electrolysis for aesthetic reasons)

11 Chemical protection Sacrificial protection - when iron or steel have magnesium alloys attached to them, the magnesium will corrode in place of the iron: The magnesium anode will need to be replaced periodically. Galvanising - iron or steel is dipped in molten zinc. This is both a coat and chemical protection, as zinc is more reactive that iron and will corrode in its place, even if the coat is broken.

12 Cathodic protection A 3rd type of rust prevention exists, which uses electricity. By making the iron or steel structure the cathode, oxidation of the metal is inhibited. This is very useful for underground or inaccessible structures. Expt: Rusting Exam questions: CC pp The Haber Process NB. The reaction is REVERSIBLE and the forward reaction is exothermic Raw materials Nitrogen: can be obtained by burning hydrogen in air. Hydrogen: Steam reformation of methane (natural gas)...

13 Optimum conditions Conditions are chosen to maximise ammonia production (and profit). These are: High pressure (200 atm) - forces equilibrium to the right (LCP). Moderate temperatures (450ºC) - low temperatures would lead to a very low reaction rate, and high temperatures would shift the equilibrium to the left, reducing the yield of ammonia. Catalyst - beds of IRON Liquid ammonia is constantly removed, which shifts the equilibrium to the right.

14 Uses of Ammonia NB. Ammonia is extremely soluble in water (fountain expt) due to the reaction that takes place: 1. The manufacture of NITRIC ACID (used to make nylon, explosives,..) 2. Household cleaning products 3. Major use - Fertilisers Ammonium salts can be produced by reacting ammonia with acids: EQNS: Fertilisers have NPK values - nitrogen, phosphorus and potassium - to promote growth in plants. Write the formulae for: Ammonium phosphate Potassium sulphate Ammonium sulphate

15 Draw a dot and cross diagram for: Ammonia Ammonium Ions Problems caused by the use of synthetic fertilisers EUTROPHICATION The soluble fertiliser gets into the river system and causes ALGAE to grow rapidly. This covers the surface stopping light from reaching the river bed, and depletes the oxygen in the water, causing plant life, fish and other animals to die. Note: The decomposition of the dead organic matter is a source of methane in the atmosphere, an important greenhouse gas. BLUE BABIES Nitrates are difficult and expensive to remove from drinking water. Consumption causes illness, and can tinge the skin of infants blue.

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