Chemistry - an illustrated guide to science (794128), страница 20
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Less reactive metals donot burn but form a surfacelayer of oxide. Metals at thebottom of the reactivity seriesare not oxidized byatmospheric oxygen.AgHgdo not burnor oxidizeon surfaceReaction with O2(g)on heating● MetalsCudo not burn,but onlyform a surfacelayer of oxide● Metalscan be arranged inorder of their reactivity,starting with the most reactive.This is called the reactivityseries. The relative reactivity ofmetals is reflected through allof their chemistry.PbFeReaction with coldwater● Metalsat the top of thereactivity series react readilywith cold water but withdecreasing vigor down tomagnesium.
The metals belowmagnesium do not react withcold water.Reaction withcold waterdisplace H2(g)from cold waterwith decreasingreactivityK, violentlydisplace H2(g)from cold waterwith decreasingreactivityMg, very slowlydo not displaceH2(g) fromcold waterdo not displaceH2(g) fromcold waterReaction withsteamdisplace H2(g)from steam withdecreasing vigorK, very violentlydisplace H2(g)from steam withdecreasing vigorFe, very slowly)do not displaceH2(g) from steamdo not displaceH2(g) from steamReaction withdilute aciddisplace H2(g)from diluteacid withdecreasing vigorK, explosivelydo not displaceH2(g) fromdilute aciddo not displaceH2(g) fromdilute acidReaction with steam● Metalsreact more vigorouslywith steam than with coldwater.
All of the metals downto iron react with steam withdecreasing vigor. The metalsbelow iron do not react withsteam.© Diagram Visual Information Ltd.Reaction with diluteacid● Allof the metals down to leadreact with dilute acids, withdecreasing vigor. The metalsbelow lead do not react withdilute acids.Mg,very vigorousFe,steadilyPb, very slowly115Tests on metals:flame testPATTERNS—METALSKey wordsionsaltsolution1 Flame test1 Flame test● Severalmetal ion s producecharacteristic colors when introducedto a bunsen flame either as a solid oras a solu tion of a salt.● A clean platinum or nichrome wire isdipped in concentrated hydrochloricacid and then into the solid orsolution.● The sample is introduced to themiddle of a non-luminous bunsenflame.flamecolorplatinum or nichrome wiresample2 Flame coloration2 Table of flame colorationColor of flameLikely ion presentMetalApple greenBa2+bariumBlue-greenCu2+copperBrick redCa2+calciumCrimsonSr 2+strontiumLilacK+potassiumOrange-yellowNa+sodiumRedLi +lithiumfollowing metals produce thefollowing colors in the flame test:barium: apple greencalcium: brick redcopper: blue-greenlithium: redpotassium: lilacsodium: orange-yellowstrontium: crimson● The lilac color of potassium issometimes difficult to see and is betterobserved through blue glass thatmakes the flame appear purple.● The orange-yellow color of sodium isvery intense and may mask the colorof other metal ions present.© Diagram Visual Information Ltd.● The116PATTERNS—METALSKey wordsamphoterichydroxideprecipitatesaltsodium hydroxidetransition metalsTests on metals:metal hydroxides1 Producing the hydroxide from the metallic salta few drops of NaOH1 Producing the hydroxide● Group1 metal hydroxides are verysoluble and form strong alkalinesolutions.
Group 2 metal hydroxidesare less soluble but still dissolvesufficiently to form weak alkalinesolutions. All other metals forminsoluble hydroxides. If several dropsof sodium hydroxide ( NaOH) solutionare added to a solution of a metal salt,a precipitate, often gelatinous, isformed.
Care must be taken whencarrying out this reaction becausesome metals form precipitates thatredissolve in excess sodiu m hydroxidesolution. If sodium hydroxide solutionis added too quickly, the initialprecipitate may not be seen.2 The reactionsreactions of metal salt solutionswith sodium hydroxide solution can beused to identify the metal.● Aluminum, zinc, and lead hydroxidesare all am photeric. When sodiumhydroxide solution is added tosolutions of salts of these metals, aninitial white precipitate is formed.However, if excess sodium hydroxidesolution is added, the precipitatedissolves, forming a solution of asoluble complex compound.metal saltsolutionAdd a small amount of NaOHto metal salt solutioninsoluble metalhydroxideA jelly-like solid forms2 The reactionsAluminum nitrate → white precipitate of aluminum hydroxideAl(NO3) 3 + 3NaOH → 3NaNO3 + Al(OH) 3 ↓● TheAl(OH) 3(s) + NaOH(aq) ➞Na[ Al(OH) 4 ] (aq)sodium tetrahydroxoaluminate(III)Zn(OH) 2(s) + 2NaOH(aq) ➞Na2[ Zn(OH) 4 ] (aq)© Diagram Visual Information Ltd.sodium tetrahydroxozincate(II)Pb(OH) 2(s) + 2NaOH(aq) ➞Na2[ Pb(OH) 4 ] (aq)sodium tetrahydroxoplumbate(II).and copper are tran sition m etalsand form characteristic coloredprecipitates with sodium hydroxidesolution.● IronZinc nitrate → white precipitate of zinc hydroxideZn(NO3) 2 + 2NaOH → 2NaNO3 + Zn(OH) 2 ↓Lead nitrate → white precipitate of lead hydroxidePb(NO3) 2 + 2NaOH → 2NaNO3 + Pb(OH) 2 ↓Iron(II) nitrate → green precipitate of iron(II) hydroxideFe(NO3) 2 + 2NaOH → 2NaNO3 + Fe(OH) 2 ↓Iron(III) nitrate → rust-brown precipitate of iron(III) hydroxideFe(NO3) 3 + 3NaOH → 3NaNO3 + Fe(OH) 3 ↓Copper nitrate → royal blue precipitate of copper hydroxideCu(NO3) 2 + 2NaOH → 2NaNO3 + Cu(OH) 2 ↓117Tests on metals:metal ionsReacations with reagentsaddition to flame tests and theproperties of their hydroxides,the presence of some metal ions inMetal ion in solutionKey wordshydroxidereagentsolution can be demonstrated by theirreactions with particular reagents.To the test solutionPositive resultAlumnumAdd 1 or 2 drops of litmus solutionfollowed by dilute hydrochloric aciduntil the mixture is just acidic.
Thenadd ammonia solution until justalkaline.Blue lake – a gelatinous precipitateof aluminum hydroxide – is formed,and this absorbs the litmus, leavingthe solution almost colorless.BariumAdd several drops of potassiumchromate solution.A yellow precipitate of bariumchromate. Lead ions also give a yellowprecipitate, but lead chromate isdeeper yellow and turns orange onheating.CopperAdd ammonia solution drop by dropuntil it is in excess.An initial blue precipitate of copper(II)hydroxide that dissolves in excessammonia solution to give a deep bluesolution containing the complex ion[Cu(NH3) 4 ] 2+ .Iron(II)Add several drops of potassiumhexacyanoferrate(III) solution.A deep blue solution is formed.Iron(III)Add several drops of ammoniumthiocyanate solution.Deep blood-red coloration.LeadAdd several drops of potassium iodidesolution.A yellow precipitate of lead(II) iodide.SilverAdd several drops of potassiumchromate solution.A brick-red precipitate of silverchromate.ZincAdd ammonium chloride andammonia solution, then pass hydrogensulfide through the mixture.A white, or more often dirty white,precipitate of zinc sulfide.© Diagram Visual Information Ltd.● InPATTERNS—METALS118PATTERNS—METALSKey wordsalloyaluminumcopperductilegalvanizingironleadreactivity serieszincUses of metalsMetalUseReasonAluminumStructural material forships, planes, cars,cookwareElectric cablesStrong but light; oxidelayer preventscorrosion.Light, but goodconductor.ZincCoating (galvanizing)steelReactive — givessacrificial protectionto iron; does notcorrode easily.Modifies theproperties of the otherelements.Uses of metals● Theuses of metals are related to boththeir physical and chemical properties.The physical properties of a metal aresometimes altered by mixing it withother metals or non-metals to formalloys.Alloys:brass (Zn/ Cu)bronze (Zn/ Sn/ Cu)Aluminum● Alu m in u mhas a low density but is toosoft for many applications.
It isfrequently used as duralumin (an alloyof aluminum and copper) as astructural material in the manufactureof airplanes.IronStructural material forall industries (in theform of steel)Strong and cheap;properties can bemade suitable byalloying.LeadRoofingCar batteriesVery malleable anddoes not corrode.Design of batterymakes rechargingpossible.Low melting point.Zinc● Zin cis above iron in the reactivityseries. During galvan izin g, iron isdipped in molten zinc, and the layer ofzinc formed on the iron protects itfrom rusting. If the galvanized iron isscratched, exposing the iron, anelectrolytic cell forms between theiron and zinc, and the zinc corrodes inpreference to the iron.Solder (Pb/ Sn alloy)Ironis used for all sorts of structures,most often as steel (an alloy of ironand carbon).
The one serious problemwith iron and steel is that they rust onexposure to water and oxygen in theair.TTBA● IronCopperLead© Diagram Visual Information Ltd.● Leadhas a high density and isimpervious to water, so it used asflashing on roofs. It is also used as inthe manufacture of car batteries. Inthe past, before its toxic nature wasunderstood, lead was also used forwater pipes and in paints. Solder (analloy of lead and tin) is widely used tojoin copper wires and copper pipes.YERElectric cablesPipesAlloys (see above)Coins (alloyed withnickel)Very good conductor.Very ductile, does notcorrode easily.Copperis very ductile and can be easilydrawn into wires.
It is a good conductor ofelectricity and is used for the conductingparts of electric cables. Copper does not● Copperreact with water and is a good conductorof heat. It is used for water pipes andradiators.119Reactivity of metals 1CHEMICAL REACTIONSKey words1 Forming oxides and chloridesalkalicalciumchloridecopperironhydroxidemagnesiumoxidesodiuma1 Forming oxides andchlorides●ba oxygen or chlorineb burning piece of reactive metalMost metals react with air to formmetal oxides. Reactive metals likem agn esiu m burn, producing light andheat. Less reactive metals like coppersimply change color on heating:2Mg(s) + O2(g) ➞ 2MgO(s)2Cu(s) + O2 ➞ 2CuO(s)● Metalswill also form chlorides whenheated in chlorine:2 Forming hydroxidesMg(s) + Cl 2(g) ➞ MgCl 2(s)Cu(s) + Cl 2 ➞ CuCl 2(s)f2 Forming hydroxides● Veryreactive metals like calciu m andsodiu m react with water to formsolutions of metal hydroxides andhydrogen gas:deCa(s) + 2H2O(l) ➞Ca(OH) 2(aq) + H2(g)2Na(s) + 2H2O(l) ➞2NaOH(aq) + H2(g)ccdef● Calciumcalciumcold waterinverted filter funnelhydrogenhydroxide is less soluble inwater and forms a weak alkali.● Sodium hydroxide is very soluble inwater and forms a strong alkali.3 Less reactive metals3 Less reactive metalsh● Lessjreactive metals, which react withwater very slowly or not at all, reactwith steam to form metal oxides andhydrogen gas.● Magnesium reacts very slowly withwater but readily with steam:kiMg(s) + H2O(g) ➞ MgO(s) + H2(g)● Ironldoes not react with water butreacts with steam to form iron(II)diiron(III) oxide:least reactive metals, such ascopper, do not react with water orsteam.glghijklwatersafety tubesteammagnesium ribbonhydrogen ignitesheat© Diagram Visual Information Ltd.3Fe(s) + 4H2O(g) ➞ Fe3O4 (s) + 4H2(g)● The120CHEMICAL REACTIONSKey wordsanodecarbonatecathodelimewateroxidereactivity seriessulfuric acidReactivity of metals 21 Reactions of metal compoundscbdfa1 Metal compounds● Theoxides of metals that are low inthe reactivity series, like copper, canbe reduced by heating them in astream of hydrogen gas.● All group 1 metal carbon ates, with theexception of lithium carbonate, are notdecomposed on heating.
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