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Air and water

  1. 1. Air and Water Grade 10 IGCSE Chemistry
  2. 2. What you need to be able to do and understand: Describe a chemical test for water. Describe and explain, in outline, the purification of the water supply by filtration and chlorination. State some of the uses of water in industry and in the home. Describe the separation of oxygen and nitrogen from liquid air by fractional distillation. Describe the composition of clean air as being a mixture of 78% nitrogen, 21% oxygen and small quantities of noble gases, water vapour and carbon dioxide. State the common air pollutants as carbon monoxide, sulfur dioxide and oxides of nitrogen, and describe their sources. Explain the presence of oxides of nitrogen in car exhausts and their catalytic removal. Describe the rusting of iron in terms of a reaction involving air and water, and simple methods of rust prevention, including paint and other coatings to exclude oxygen.
  3. 3. How do you know something is water? The tests for water – there are TWO things you can do: 1. Add a few drops to white anhydrous copper(II) sulphate. • If it turns from white to blue then it’s water! 2. Dip in a piece of dry blue cobalt chloride paper. • If it turns from blue to pink then it’s water!
  4. 4. We need water all the time – how do we purify it? 1. A screen 1 2. A coagulant is added 3. Air is added – flotation tanks. Then the sludge is skimmed off. 4. Sand and other filters 5. Disinfection with chlorine or fluorine 6. Storage in a reservoir 2 3 4 5 6
  5. 5. 1. A screen traps any large particles such as twigs. 2. A coagulant is added – a chemical to make small suspended particles stick together. 3. Next, air is blown through the water in flotation tanks, to make the coagulated particles float to the top. They are skimmed off. 4. The water is passed through a bed of fine sand to filter it • It may go through further filters like charcoal to remove bad tastes and smells. 5. Chlorine is added to kill bacteria. Fluorine can also be added to help fight tooth decay. 6. The water is pumped to a storage reservoir, ready for you!
  6. 6. Uses of water – this is not that hard…;) Water in industry Water is an important raw material and has many uses. It is used as a solvent and as a coolant both in the home and in industry. It is used in many important industrial processes including the manufacture of sulphuric acid. Seawater/brine is a valuable resource e.g. large scale evaporation in 'salt pans' (using fuel burning or solar energy) to produce 'sea salt' sodium chloride NaCl, the water also contains lots of other salts including bromides from which the element bromine is extracted. The water cycle. Water is the most abundant substance on the surface of our planet and is essential for all life. Water in rivers, lakes and the oceans is evaporated by the heat of the Sun (endothermic – it absorbs energy thus cooling our planet). The water vapour formed rises into the atmosphere, cools and forms clouds of condensation (exothermic – releasing energy). Eventually this gives rain and snow 'precipitation' which on melting returns to the rivers, seas and oceans.
  7. 7. What is in our air? –again this is not that hard…;) Clean air is as a mixture of: • 78% nitrogen • 21% oxygen • 1% - small quantities of: • noble gases • water vapour • carbon dioxide.
  8. 8. How do you separate oxygen and nitrogen from air? Air is a mixture of gases – they all have different boiling points! Start at 3 min end at 6:30 Boiling points of gases (°C): • CO2 -32 • O2 -183 • N2 -196 3. Liquefied air is then passed into the bottom of a fractionating column – the column is warmer at the bottom. 4. Liquid N2 boils first where it is piped off 5. Liquid O2 collects at the bottom 1. Air is filtered to remove dust 2. Air is cooled in stages until -200°C. During this process: • H2O condensed and was removed at 0°C • CO2 freezes at -79°C and is removed W A R M E R
  9. 9. ACK! I can’t breath! Pollutant How is it formed? What harm does it do? Carbon monoxide (CO) colourless gas, insoluble, no smell Burning of fossil fuels in too little air (inside car engine and furnaces) Poisonous even in small amounts. Blocks oxygen receptors in haemoglobin – so you suffocate. Sulfur dioxide (SO2) an acid gas with a sharp smell Burning of fossil fuels – especially in power stations Eye and throat irritant and causes respiratory problems. Dissolves in water to form acid rain. Nitrogen oxides (NO2 & NO) acidic gases Burning of fossil fuels – then a reaction happens with NOx and O2 Respiratory problems and dissolves in water to form acid rain. Lead compounds Burning of fossil fuels (a long time ago tetra-ethyl lead was added to gas – now it is only used in some countries) Lead poisoning damages children’s brains. Damages kidneys and nervous systems in adults. AIR POLLUTION!
  10. 10. burning less fuel by having more efficient engines using low sulfur fuels using catalytic converters, which convert nitrogen monoxide to nitrogen and oxygen, and carbon monoxide to carbon dioxide adjusting the balance between public and private transport, with more people using buses and trains instead of cars How do you reduce air pollution? Atmospheric pollution caused by the exhaust given out by cars can be reduced by: NO & CO A catalytic converter – you can find this in your car N2, O2 & CO2 in out But is CO2 harmless?
  11. 11. NO & CO in N2, O2 & CO2 out Why do you think its called a catalytic converter? Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. In the catalytic converter, there are two different types of catalysts at work: a reduction catalyst and an oxidation catalyst. In A: NO is reduced: 2NO(g) → N2(g) + O2(g) A In B: CO is oxidised: 2CO(g) + O2(g) → 2CO2(g) B
  12. 12. Rust! – when air and water collide After several days what will you see? Place nails in test tubes like this: Air and water: Water, no air: Air, no water: Rust! No rust No rust Rusting needs oxygen AND water. The iron has been oxidised. 4Fe(s) + 2H2O(l) + 3O2(g) → 2Fe2O3·2H2O(s) What are some ways to prevent rusting?
  13. 13. What are some ways to prevent rusting? Cover the iron (to keep out oxygen and water): • Paint • Grease • Another metal (galvanising with zinc, electroplating with tin) Cover the iron (to keep out oxygen and water): • Paint • Grease • Another metal (galvanising with zinc, electroplating with tin) Let another metal corrode instead: Use magnesium or zinc as they are more reactive than iron. This is called sacrificial protection.
  14. 14. The last bit from Stoichiometry… Use the molar gas volume, takes as 24dm3 at room temperature and pressure Calculate stoichiometric reacting masses and reacting volumes of solutions; solution concentrations will be expressed in mol/dm3 (calculations involving the idea of limiting reactants may be set) Fluorine F2 38g Chlorine Cl2 71g Oxygen O2 32g Imagine 3 containers each with a volume of 24dm3 (cubic decimeter) and each is at standard room temperature and pressure. Standard room temperature and pressure is SET to 20°C and 1 ATM – which we say rtp for short – standard room temperature and pressure. What do all of these containers have in common? They all contain 1 mole! 1mole 1mole 1mole
  15. 15. So we can conclude that 1 mole of every gas occupies the same volume, at the same temperature and pressure. At room temperature and pressure this is 24dm3. This is also called its molar volume. A Cloud A has nitrogen dioxide NO2 B Cloud B has oxygen O2 Here are two clouds – they have identical volumes and are at the same temperature and pressure. Do they also have the same number of moles? YES! at rtp it is: 1 mole How much does each cloud weigh? Cloud A: NO2 = 46g Cloud B: O2 = 32g
  16. 16. Volume at rtp (dm3) No. of moles 24dm3 Use this triangle to help you with these problems. Cover the one you need to find out! Calculating gas volumes from moles and grams 1. What volume does 0.25 moles of a gas occupy at rtp? 2. What volume does 22grams of carbon dioxide gas occupy at rtp? 1 mole occupies 24dm3 so: 0.25moles occupies 0.25 x 24dm3 = 6dm3 (or 6000cm3) at rtp. Molar mass of CO2 = 44g/mol so: 22grams = 0.5mole 0.5moles occupies 0.5 x 24dm3 = 12dm3 (or 12000cm3) at rtp.
  17. 17. Volume at rtp (dm3) No. of moles 24dm3 Use this triangle to help you with these problems. Cover the one you need to find out! Calculating gas volumes from equations 1. What volume of hydrogen will react with 24dm3 of oxygen to form water? 2. When sulfur burns in air it forms sulfur dioxide. What volume of this gas is produced when 1g of sulfur burns? 2H2(g) + O2(g) → 2H2O(l) so: Mole ratio between H2 and O2 is 2:1 therefore 2 x 24dm3 = 48dm3 at rtp. S(s) + O2(g) → SO2(g) and molar mass of S is 32g/mol so: 1g = how many moles? = 1/32 = 0.031moles of S. Mole ratio between S and SO2 is 1:1 therefore 0.031moles of SO2 0.031 x 24dm3 = 0.75dm3 at rtp.

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