metal salts：金属盐

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1、METALSALTSpHSCALEWhenasubstancedissolvesinwater,itformsanaqueoussolution,whichmaybeacidic,alkalineorneutral.Indicators,forexamplelitmus,canbeusedtoshowwhetherasolutionisacidic,alkalineorneutralbythewaytheircolourschange.Universalindicatorcanshow,inaddition,howacidicoralkalineasolution

2、is.TheacidityoralkalinityofasolutionisexpressedasitspHnumber:pH01234567891011121314increasingacidityneutralincreasingalkalinityAcidshaveapHlessthan7whereasalkalis/baseshaveapHgreaterthan7.AcidsdissolveinwatertoproduceH+ions.Thiswaswhatmakesthesolutionacidic.Alkalisaresolublebaseswhich

3、dissolveinwatertoproduceOH-ions.Acidsandalkaliscanbeusedtoneutraliseeachotherastheyreacttoproducewater(pH7).H++OH-H20METHODSFORMAKINGSALTSThereareseveralmethodsformakingsalts.Themethodchosendependson:·whetherthesaltreactswithwater·whetherthesaltissolubleorinsolubleinwater·whethertheme

4、talcontainedinthesaltisareactiveorunreactivemetal1.PRECIPITATIONWhenasaltisinsolubleinwater,itispreparedbyprecipitation.Asolutionofasolublesaltcontainingthedesiredmetalion(usuallythemetalnitrate)isaddedtoasolutioncontainingthedesirednegativeion(usuallyasitssodiumsalt).Thetwoionscombin

5、eimmediatelytogiveaprecipitate(asolid).Theprecipitateisfilteredoff,washedwithwateranddried.e.g.tomakelead(II)iodide,asolutionoflead(II)nitrateisaddedtoasolutionofsodiumiodidePb(NO3)2(aq)+2NaI(aq)PbI2(s)+2NaNO3(aq)Pb2+(aq)+2I-(aq)PbI2(s)e.g.tomakebariumsulphate,asolutionofbariumnitrate

6、isaddedtoasolutionofsodiumsulphateBa(NO3)2(aq)+Na2SO4(aq)BaSO4(s)+2NaNO3(aq)Ba2+(aq)+SO42-(aq)BaSO4(s)TOPIC11.2.5:SALTS&ELECTROLYSIS92.SOLUBLESALTSTherearethreemethodsformakingsolublesalts:·thereactionofanacidwithareactivemetal·thereactionofanacidandaninsolublemetaloxide(orhydroxide)·

7、thereactionofanacidandaninsolublemetalcarbonateThemethodfollowedineachcaseisthesame.a)ThereactionofanacidwithareactivemetalThereactionofanacidwithametalcanonlybeusedformetalswhichareneithertooreactivenortoounreactive,i.e.thosebetweenCaandSninclusiveinthereactivityseries.Forexample,mag

8、nesiu