Junior cycle science chemistry in action. By Theresa Lowry-Lehnen. Science Teacher.
29/05/13Junior CycleScienceJunior CycleScienceChemistry in ActionChemistry in ActionEdited and Reproduced byTheresa Lowry-LehnenRGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling, Dip Adv Psychotherapy, BSc(Hon’s) Clinical Science, PGCE (QTS) , H. Dip. Ed, MEd, Emotional Intelligence (Level 9) MHS Accredited
29/05/13Balancing equationsBalancing equationsConsider the following reaction:Na OH HH HNaOH+ +This equation doesn’t balance – there are 2 hydrogenatoms on the left hand side (the “reactants” and 3 onthe right hand side (the “products”)Sodium + water sodium hydroxide + hydrogenNa + H2O NaOH + H2
29/05/13Balancing equationsBalancing equationsWe need to balance the equation:NaOH HH HNaOHSodium + water sodium hydroxide + hydrogen+ +NaOH HNaOHNow the equation is balanced, and we can write it as:2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
29/05/13Testing for carbon dioxideTesting for carbon dioxideGasLimewater turnsmilky/cloudyLimewater
29/05/13Adding acid to carbonatesAdding acid to carbonatesCarbonates are compounds containing carbon and oxygen. When an acid isadded to a carbonate the carbonate starts to fizz. A gas called_________ _______ is produced.Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + waterCaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)2
29/05/13Flame testsFlame testsCompoundCompound Colour of flameColour of flame
29/05/13Flame testsFlame testsCompounds containing lithium, sodium, potassium, calcium andbarium can be recognised by burning the compound andobserving the colours produced:LithiumRedSodiumYellowPotassiumLilacCalciumBrick redBariumGreen
29/05/13Metal ionsMetal ionsMetal compounds in a solution contain metal ions. For example,consider calcium chloride:Chlorine is ingroup 7 so achloride ionwill be Cl-Calcium is ingroup 2 and hastwo electrons inits outer shell, soit will form a Ca2+ion.Calcium chloride has the formula CaCl2
29/05/13Metal ions and precipitatesMetal ions and precipitatesSome metal ions form precipitates, i.e. an insoluble solid thatis formed when sodium hydroxide is added to them. Considercalcium chloride:Ca2+(aq) + OH-Ca(OH)2 (s)2
29/05/13Metal ions and precipitatesMetal ions and precipitatesSome metal ions form precipitates, i.e. an insoluble solid thatis formed when sodium hydroxide is added to them. Considercalcium chloride:Ca2+(aq) + OH-Ca(OH)2 (s)2Metal ionMetal ion Precipitate formedPrecipitate formed ColourColourCalcium Ca2+ Calcium hydroxide: Ca2+(aq) + OH-(aq) Ca(OH)2 (s) WhiteAluminium Al3+Magnesium Mg2+Copper(II) Cu2+Iron(II) Fe2+Iron(III) Fe3+
29/05/13Testing for chloride and sulphate ionsTesting for chloride and sulphate ionsTest 1: Chloride ionsAdd a few drops of dilute nitric acid to the chloride ionsolution followed by a few drops of silver nitrate.Test 2: Sulphate ionsAdd a few drops of dilute hydrochloric acid to the sulphateion solution followed by a few drops of barium chloride.Precipitate formed = silver chloride (white)Precipitate formed = barium sulphate (white again)For each test state: 1) The colour of the precipitate2) What compound it is
29/05/13Ammonium, nitrate, bromide and iodide ionsAmmonium, nitrate, bromide and iodide ionsAmmonium ions:Add sodium hydroxide and test the gas using damp litmuspaper – ammonia gas turns damp litmus paper blue.Nitrate ions:Add sodium hydroxide followed by aluminium powder and testusing damp litmus paper.Bromide and iodide ions:Add a few drops of dilute nitric acid followed by a few dropsof silver nitrate solution. A pale yellow precipitate should beformed for bromide ions and a darker yellow precipitate foriodide ions.
29/05/13Thermal decompositionThermal decompositionA “thermal decomposition” reaction occurs when a compoundbreaks down (“decomposition”) through the action of heat.Practical work:Perform a thermal decomposition reactionon each of these compounds and state:1) The colour changes you observed2) The reaction that happenedCopper carbonate:Zinc carbonate:CuCO3 (s) CuO(s) + CO2 (g) (Green – Black)ZnCO3 (s) ZnO(s) + CO2 (g) (White – Yellow)
29/05/13Sulphuric acidSulphuric acidSulphuric acid has many important uses – car batteries, detergents,fertilisers etc.How sulphuric acid is made:Step 1: Burn sulphur in air:Step 2: Pass the sulphur dioxide over a vanadium oxide catalyst at 450OC:Step 3: Dissolve the sulphur trioxide in sulphuric acid:Step 4: Add water to the oleum:Sulphur + oxygen sulphur dioxideSulphur trioxide + conc. sulphuric acid oleumSulphur dioxide + oxygen sulphur trioxideOleum + water sulphuric acid
29/05/13Reversible ReactionsReversible ReactionsWhen a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactantsare added or taken away) an EQUILIBRIUM is achieved – in other words,the reaction goes at the same rate in both directions:A + B C + DEndothermic reactionsIncreased temperature:Decreased temperature:A + B C + DA + B C + DMore productsLess productsExothermic reactionsIncreased temperature:Decreased temperature:A + B C + DLess productsMore productsA + B C + D
29/05/13Sulphuric acidSulphuric acidStep 2 in the manufacture of sulphuric acid is an example of areversible reaction:2SO2 + O2 2SO3ExothermicEndothermicWhat would happen if the temperature was decreased?Solution – use 450OC as a compromiseThe reaction would favour the production of sulphur trioxideBUT the reaction would happen at a slower rate.
29/05/13Iron and SteelIron and SteelIn previous work we considered the role of theblast furnace in extracting iron from its ore.The iron contains roughly 5% carbon anddifferent metals and is very ________. Inorder to reduce these impurities and convertthe iron into _________ the molten iron istransferred into another furnace where it ismixed with recycled scrap iron and pure___________. The oxygen reacts with themetal impurities to form ________ oxides.Calcium carbonate is also added to removesome of the acidic oxides as _______ whenthe furnace is tilted.Words – slag, brittle, steel, oxygen, acidic
29/05/13Making steel – the reactionsMaking steel – the reactions1) Mixing oxygen with silicon impurities:2) Decomposition of limestone:3) Adding these products together:Silicon + oxygen Silicon oxideCalcium carbonate calcium oxide + carbon dioxideSilicon oxide + calcium oxide calcium silicateSteel with a highcarbon content isstrong but brittleSteel with a lowcarbon content iseasily shapedSteel with chromiumand nickel is calledstainless steel
29/05/13TitaniumTitaniumTitanium is a strong metal used in planes, replacement hipjoints, bikes etc. Two steps are used in its manufacture:Step 1: Convert titanium dioxide (ore) to titanium chlorideStep 2: Displace the titanium using sodium or magnesium:Titanium chloride + sodium titanium + sodium chlorideIn this reaction thetitanium is displaced my amore reactive metal. Thisreaction is done in an argonatmosphere to avoid anyfurther reactions.Titanium ions have acharge of 4+ and gain fourelectrons to becometitanium atoms. This is areduction reaction.
29/05/13AluminiumAluminiumAluminium is a fairly reactive metal that doesn’tcorrode due to forming a thin layer ofaluminium oxide. This explains why greenhousesdon’t rust and don’t need to be painted.A thicker layer of aluminium oxide can be made artificially.There are two stages:1) Remove the natural layerby placing the aluminium insodium hydroxide.2) Use electrolysis onsulphuric acid with thealuminium as the positiveelectrode. This is calledanodising.++++----H2SO4Al