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Air and water


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IGCSE, air and water, chemistry

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Air and water

  1. 1. Air and WaterGrade 10 IGCSE Chemistry
  2. 2. What you need to be able to do andunderstand:Describe a chemical test for water.Describe and explain, in outline, thepurification of the water supply byfiltration and chlorination.State some of the uses of water inindustry and in the home.Describe the separation of oxygenand nitrogen from liquid air byfractional distillation.Describe the composition of clean airas being a mixture of 78% nitrogen, 21%oxygen and small quantities of noblegases, water vapour and carbondioxide.State the common air pollutants ascarbon monoxide, sulfur dioxide andoxides of nitrogen, and describe theirsources.Explain the presence of oxides ofnitrogen in car exhausts and theircatalytic removal.Describe the rusting of iron in terms ofa reaction involving air and water, andsimple methods of rustprevention, including paint and othercoatings to exclude oxygen.
  3. 3. How do you know somethingis water?The tests for water – there are TWO things you can do:1. Add a few drops to white anhydrouscopper(II) sulphate.• If it turns from white to blue then it’swater!2. Dip in a piece of dry blue cobalt chloridepaper.• If it turns from blue to pink then it’swater!
  4. 4. We need water all the time – how do we purify it?1. A screen12. A coagulant is added3. Air is added –flotation tanks.Then the sludge isskimmed off.4. Sand and otherfilters5. Disinfection withchlorine or fluorine6. Storage ina reservoir23456
  5. 5. 1. A screen traps any large particles such astwigs.2. A coagulant is added – a chemical to makesmall suspended particles stick together.3. Next, air is blown through the water inflotation tanks, to make the coagulatedparticles float to the top. They areskimmed off.4. The water is passed through a bed of finesand to filter it• It may go through further filters likecharcoal to remove bad tastes andsmells.5. Chlorine is added to kill bacteria. Fluorinecan also be added to help fight toothdecay.6. The water is pumped to a storagereservoir, ready for you!
  6. 6. Uses of water– this is not that hard…;)Water in industryWater is an important raw material and has many uses. It is used as a solvent and as acoolant both in the home and in industry. It is used in many important industrialprocesses including the manufacture of sulphuric acid.Seawater/brine is a valuable resource e.g. large scale evaporation in salt pans (usingfuel burning or solar energy) to produce sea salt sodium chloride NaCl, the water alsocontains lots of other salts including bromides from which the element bromine isextracted.The water cycle.Water is the most abundant substance on the surface of our planet and is essential forall 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 formedrises into the atmosphere, cools and forms clouds of condensation (exothermic –releasing energy). Eventually this gives rain and snow precipitation which on meltingreturns 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 separateoxygen and nitrogenfrom air?Air is a mixture of gases – they allhave different boiling points!Start at 3 minend at 6:30Boiling points of gases (°C):• CO2 -32• O2 -183• N2 -1963. Liquefied air is then passed into the bottomof a fractionating column – the column iswarmer at the bottom.4. Liquid N2 boils first where it is piped off5. Liquid O2 collects at the bottom1. Air is filtered to remove dust2. 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 removedWARMER
  9. 9. ACK! I can’t breath!Pollutant How is it formed? What harm does it do?Carbon monoxide(CO)colourless gas, insoluble,no smellBurning of fossil fuels in too little air(inside car engine and furnaces)Poisonous even in small amounts.Blocks oxygen receptors inhaemoglobin – so you suffocate.Sulfur dioxide (SO2)an acid gas with a sharpsmellBurning of fossil fuels – especially inpower stationsEye and throat irritant and causesrespiratory problems. Dissolves inwater to form acid rain.Nitrogen oxides(NO2 & NO)acidic gasesBurning of fossil fuels – then areaction happens with NOx and O2Respiratory problems and dissolvesin water to form acid rain.Lead compoundsBurning of fossil fuels (a long timeago tetra-ethyl lead was added to gas– now it is only used in somecountries)Lead poisoning damages children’sbrains. Damages kidneys and nervoussystems in adults.AIR POLLUTION!
  10. 10. burning less fuel by having more efficientenginesusing low sulfur fuelsusing catalytic converters, which convertnitrogen monoxide to nitrogen andoxygen, and carbon monoxide to carbondioxideadjusting the balance between public andprivate transport, with more people usingbuses and trains instead of carsHow do you reduce airpollution?Atmospheric pollution caused by the exhaust given out by cars can bereduced by:NO & COA catalytic converter – youcan find this in your carN2, O2 &CO2inoutBut is CO2 harmless?
  11. 11. NO & COin N2, O2 &CO2outWhy do you think its called a catalytic converter?Both types consist of a ceramic structure coated with a metal catalyst, usuallyplatinum, rhodium and/or palladium.In the catalytic converter, there are twodifferent types of catalysts at work: areduction catalyst and an oxidationcatalyst.In A: NO is reduced:2NO(g) → N2(g) + O2(g)AIn B: CO is oxidised:2CO(g) + O2(g) → 2CO2(g)B
  12. 12. Rust! – when air and water collideAfter several days what will you see?Place nails in test tubes like this:Air and water:Water, no air:Air, no water:Rust!No rustNo rustRusting 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 preventrusting?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. Thisis called sacrificial protection.
  14. 14. The last bit from Stoichiometry…Use the molar gas volume, takes as 24dm3 at room temperature andpressureCalculate stoichiometric reacting masses and reacting volumes of solutions;solution concentrations will be expressed in mol/dm3 (calculations involvingthe idea of limiting reactants may be set)Fluorine F238gChlorine Cl271gOxygen O232gImagine 3 containers each with a volume of 24dm3(cubic decimeter) and each is at standard roomtemperature and pressure. Standard room temperatureand pressure is SET to 20°C and 1 ATM – which we sayrtp for short – standard room temperature andpressure.What do all ofthesecontainershave incommon?They allcontain1 mole!1mole 1mole 1mole
  15. 15. So we can conclude that 1 mole of every gas occupies the samevolume, at the same temperature and pressure.At room temperature and pressure this is 24dm3.This is also called its molar volume.ACloud A has nitrogendioxide NO2BCloud B has oxygen O2Here are two clouds – they have identical volumes andare at the same temperature and pressure.Do they alsohave the samenumber ofmoles?YES!at rtp it is:1 moleHow much does each cloud weigh?Cloud A: NO2 = 46g Cloud B: O2 = 32g
  16. 16. Volume atrtp (dm3)No. ofmoles 24dm3Use this triangle to help youwith these problems. Coverthe one you need to find out!Calculating gas volumes frommoles and grams1. What volume does 0.25 molesof a gas occupy at rtp?2. What volume does 22grams ofcarbon dioxide gas occupy atrtp?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 = 0.5mole0.5moles occupies 0.5 x 24dm3 = 12dm3 (or 12000cm3) at rtp.
  17. 17. Volume atrtp (dm3)No. ofmoles 24dm3Use this triangle to help youwith these problems. Coverthe one you need to find out!Calculating gas volumes fromequations1. What volume of hydrogen will reactwith 24dm3 of oxygen to form water?2. When sulfur burns in air it forms sulfurdioxide. What volume of this gas isproduced when 1g of sulfur burns?2H2(g) + O2(g) → 2H2O(l) so:Mole ratio between H2 and O2 is 2:1 therefore2 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 SO20.031 x 24dm3 = 0.75dm3 at rtp.