Acids Bases and Salts.docx
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Acids Bases and Salts.docx
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AcidsBasesandSalts
Acids,BasesandSalts
Allsubstancesareacidic,neutralorbasic(alkaline).HowacidicorbasicasubstanceisshownbyitspH.Thereareseveralotherwaysbywhichwecouldfindoutwhetherasubstanceisacidic,neutralorbasic.
pHScale:
Thisisascalethatrunsfrom0to14.SubstanceswithapHbelow7areacidic.SubstanceswithpHabove7arebasic.AndthosewithpH7areneutral.
Indicators:
Indicatorsaresubstancesthatidentifyacidityoralkalinityofsubstances.Theycannotbeusedinsolidform.
UniversalIndicator:
ThisisasubstancethatchangescolorwhenaddedtoanothersubstancedependingonitspH.Theindicatorandthesubstanceshouldbeinaqueousform.
LitmusPaperorSolution:
Thisindicatorispresentintwocolors:
redandblue.Weusebluelitmusifwewanttestasubstanceforacidity.Weuseredlitmusifwewanttotestasubstanceforalkalinity.Itsresultsare:
∙Acids:
Turnsbluelitmuspaper/solutionred,
∙Bases:
Turnsredlitmuspaper/solutionblue,
∙Neutral:
ifitisusedaspaperthecolordoesn’tchange.Ifitisusedassolutionitturnspurple.
Note:
usedamplitmuspaperiftestinggases.
Phenolphthalein:
Thisisanindicatorthatisusedtotestforalkalinitybecauseitiscolorlessifusedwithanacidicorneutralsubstanceanditispinkifitisusedwithabasicsubstance.
MethylOrange:
Thisindicatorgivesfirecolors:
Redwithacids,yellowwithneutralsandorangewithbases.
Acids:
Acidsaresubstancesmadeofahydrogenionandnon-metalions.Theyhavethefollowingproperties:
∙TheydissolveinwaterproducingahydrogenionH+,
∙Theyhaveasourtaste,
∙Strongonesarecorrosive,
∙TheirpHislessthan7.
Allacidsmustbeinaqueousformtobecalledanacid.ForexampleHydrochloricacidishydrogenchloridegasdissolvedinwater.Themostcommonacidsare:
∙HydrochloricacidHCl,
∙SulphuricAcidH2SO4,
∙NitricAcidHNO3,
∙CirtricAcid,
∙CarbonicAcidH2CO3.
StrengthofAcids:
OneofthemostimportantpropertiesofacidsisthatitgiveshydrogenionH+whendissolvedinwater.ThisiswhytheamountofH+ionstheacidcangivewhendissolvedinwateriswhatdeterminesitsstrength.Thisiscalledionizationordissociation.Themoreionizedtheacidisthestrongeritis,theloweritspH.ThemoreH+ionsgivenwhentheacidisdissolvedinwaterthemoreionizedtheacidis.
StrongAcids:
HavepH’s:
0,1,2,3
Theyarefullyionized
Whendissolvedinwater,theygivelargeamountsofH+ionsExamples:
HydrochloricAcid
SulfuricAcid
NitricAcid
WeakAcids:
HavepH’s:
4,5,6
Theyarepartiallyionized
Whendissolvedinwater,theygivesmallamountsofH+ionsExamples:
Ethanoicacid(CH3COOH)
CitricAcid
CarbonicAcid
Hydrochloricacidisastrongacid.WhenitisdissolvedinwaterallHClmoleculesareionizedintoH+andCl-ions.Itisfullyionized.
EthanoicacidhastheformulaCH3COOH.Itisaweakacid.Whenitisdissolvedinwater,onlysomeoftheCH3COOHmoleculesareionizedintoCH3COO-andH+ions.Itispartiallyionized.
Note:
AcidswithpH3or4canbeconsideredmoderateinstrength.
Solutionsofstrongacidsarebetterconductorsofelectricitythansolutionsofweakacids.Thisisbecausetheycontainmuchmorefreemobileionstocarrythecharge.
Concentratedacidsarenotnecessarilystrong.Theconcentrationofanacidonlymeanstheamountofmoleculesoftheaciddissolvedinwater.Concentratedacidshavealargeamountofacidmoleculesdissolvedinwater.Diluteacidshaveasmallamountofacidmoleculesdissolvedinwater.Concentrationisnotrelatedtostrengthoftheacids.Strongacidsarestillstrongeveniftheyarediluted.Andweakacidsarestillweakeveniftheyareconcentrated.
Bases:
BasesaresubstancesmadeofhydroxideOH-ionsandametal.Basescanbemadeof:
∙Metalhydroxide(metalion&OH-ion)
∙Metaloxides
∙Metalcarbonates(metalion&CO32-)
∙Metalhydrogencarbonate(Bicarbonate)
∙Ammoniumhydroxide(NH4OH)
∙AmmoniumCarbonate((NH4)2CO3)
Propertiesofbases:
∙Bittertaste
∙Soapyfeel
∙HavepH’sabove7
∙Strongonesarecorrosive
Somebasesarewatersolubleandsomebasesarewaterinsoluble.Watersolublebasesarealsocalledalkalis.
Likeacids,alkalis'strengthisdeterminedbyitsabilitytobeionizedintometalandhydroxideOH-ions.Completelyionizedalkalisarethestrongestandpartiallyionizedalkalisaretheweakest.Ammoniumhydroxideisoneofthestrongestalkaliswhileweakalkalisincludethehydroxidesofsodium,potassiumandmagnesium.
TypesofOxides:
BasicOxides
Theyaremetaloxides
Theyreactwithacidsformingasaltandwater
Theyaresolids
Theyareinsolubleinwaterexceptgroup1metaloxides.
Theyreactwithanacidformingsaltandwater
Examples:
Na2O,CaOandCuO
AmphotericOxides
TheseareoxidesofAluminum,Zinc&Lead
Theyactasanacidwhenreactingwithanalkali&viceversa
Theirelement’shydroxidesareamphoterictoo
Theyproducesaltandwaterwhenreactingwithanacidoranalkali.
AcidicOxides
Theyareallnon-metaloxidesexceptnon-metalmonoxides
Theyaregases
Theyreactwithanalkalitoformsaltandwater
Note:
metalmonoxidesareneutraloxides
Examples:
CO2,NO2,SO2(acidicoxides)&CO,NO,
H2O(neutraloxides)
Salts:
Asaltisaneutralioniccompound.Saltsareoneoftheproductsofareactionbetweenanacidandabase.SaltsareformedinreactionsInwhichtheH+ionfromtheacidisreplacedbyanyothermetalion.Somesaltsaresolubleinwaterandsomeareinsoluble.
SolubleSalts:
AllNitrates
AllhalidesEXCEPTAgClandPbCl2
AllsulfatesEXCEPTCaSO4,BASO4,PbSO4
Allgroup1metalssalts
Allammoniumsalts
InsolubleSalts:
Silverandleadchlorides(AgCl&PbCl2)
Calcium,bariumandleadsulphates(CaSO4,BASO4,PbSO4)
AllcarbonatesEXCEPTgroup1metalsandammoniumcarbonates
PreparingSolubleSalts:
DisplacementMethod(ExcessMetalMethod):
Metal+Acid→Salt+Hydrogen
Note:
thistypeofmethodissuitabletoformakingsaltsofmoderatelyreactivemetalsbecausehighlyreactivemetalslikeK,NaandCawillcauseanexplosion.ThismethodisusedwiththeMAZIT(Magnesium,Aluminum,Zinc,IronandTin)metalsonly.
Example:
setupanexperimenttoobtainmagnesiumchloridesalt.
Mg+2HCl→MgCl2+H2
1.Add100cm3ofdilutehydrochloricacidtoabeaker
2.Addexcessmassofpowderedmagnesium
3.Whenthereactionisdone,filterthemixturetogetridofexcessmagnesium(residue)
4.Thefiltrateismagnesiumchloridesolution
5.Toobtainmagnesiumchloridepowder,evaporatethesolutiontilldryness
6.Toobtainmagnesiumchloridecrystals,heatthesolutionwhilecontinuouslydippingaglassrodinthesolution
7.Whenyouobservecrystalsstartingtoformontheglassrod,turnheatoffandleavethemixturetocooldownslowly
8.Whenthecrystalsareobtained,drythembetweentwofilterpapers
Observationsofthistypeofreactions:
∙Bubblesofcolorlessgasevolve(hydrogen).Totestapproachalightedsplintifhydrogenispresentitmakesapopsound
∙Thetemperaturerises(exothermicreaction)
∙Themetaldisappears
Youknowthereactionisoverwhen:
∙Nomoregasevolves
∙Nomoremagnesiumcandissolve
∙Thetemperaturestopsrising
∙Thesolutionbecomesneutral
ProtonDonorandAcceptorTheory:
Whenanacidandabasereact,waterisformed.TheacidgivesawayanH+ionandthebaseacceptsittoformwaterbybondingitwiththeOH-ion.AhydrogenionisalsocalledaprotonthisiswhyanacidcanbecalledProtonDonorandabasecanbecalledProtonAcceptor.
NeutralizationMethod:
Acis+Base→Salt+Water
Note:
Thismethodisusedtomakesaltsofmetalsbelowhydrogeninthereactivityseries.Ifthebaseisametaloxideormetalhydroxide,theproductswillbesaltandwateronly.Ifthebaseisametalcarbonate,theproductswillbesalt,waterandcarbondioxide.
Type1:
Acid+MetalOxide→Salt+Water
Toobtaincoppersulfatesaltgivencopperoxideandsulfuricacid:
CuO+H2SO4→CuSO4+H2O
∙Add100cm3ofsulfuricacidtoabeaker
∙AddexcessmassofCopperoxide
∙Whenthereactionisover,filtertheexcesscopperoxideoff
∙Thefiltrateisacoppersulfatesolution,toobtaincoppersulfatepowderevaporatethesolutiontilldryness
∙Toobtaincoppersulfatecrystals,heatthesolutionwhitecontinuouslydippingaglassrodinit
∙Whenyouobservecrystalsstartingtoformontheglassrod,turnheatofandleavethemixturetocooldownslowly
∙Whenyouobtainthecrystalsdrythembetweentwofilterpapers
Observationsofthisreaction:
∙Theamountofcopperoxidedecreases
∙Thesolutionchangescolorfromcolorlesstoblue
∙Thetemperaturerises
∙Youknowthereactionisoverwhen
∙Nomorecopperoxidedissolves
∙Thetemperaturestopsrising
∙Thesolutionbecomeneutral
Type2:
Acid+MetalHydroxide→Salt+Water
toobtainsodiumchloridecrystalsgivensodiumhydroxideandhydrochloricacid:
HCl+NaOH→NaCl+H2O
∙Add100cm3ofdilutehydrochloricacidtoabeaker
∙Addexcessmassofsodiumhydroxide
∙Whenthereactionisover,filtertheexcesssodiumhydroxideoff
∙Thefiltrateissodiumchloridesolution,toobtainsodiumchloridepowder,evaporatethesolutiontilldryness
∙Toobtainsodiumchloridecrystals,hearthesolutionwhilecontinuouslydippingaglassrodinit
∙Whencrystalsstarttoformontheglassrod,turnheatoffandleavethemixturetocooldownslowly
∙Whenthecrystalsareobtained,drythembetweentwofilterpapers
Observations:
∙Sodiumhydroxidestartsdisappearing
∙Temperaturerise
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