Chemical knowledge inductiontheoretical part.docx
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Chemical knowledge inductiontheoretical part.docx
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Chemicalknowledgeinductiontheoreticalpart
Chemicalknowledgeinduction2(theoreticalpart)
Two.Theoreticalpart
Theapplicationoflawtothehydrolysisofsalts:
Saltionwithwateroutoftheionizationofhydrogenionsorhydroxylionsgeneratedweakelectrolytereactioniscalledhydrolysisofsalts.
Itsgeneralruleis:
whoisweak,whohydrolysis,whoisstrongerthanothers;thetwoisnothydrolyzed;thetwoweakismorehydrolysis;theweakerthemorehydrolysis.
So,inwhatcasesdoyouconsiderthehydrolysisofsalt?
1.toanalyzeandjudgetheacidityandalkalinityofsaltsolution,weshouldconsiderhydrolysis.
2.thehydrolysisofsaltshouldbetakenintoaccountwhendeterminingthespeciesandconcentrationofionsinthesaltsolution.
SuchasNa2Ssolutioncontainsions,accordingtotheconcentrationfromlargetosmallorder:
C(na+),>c(s2-),>c(oh-),>c(hs-),>c(h+)
Or:
C(na+),+c(h+),=2c(s2-),+c(hs-),+c(oh-)
3.thehydrolysisofsaltshallbetakenintoconsiderationwhenpreparingcertainsaltsolutions
SuchasthepreparationofFeCl3,SnCl4,Na2SiO3andothersaltsolution,theyshouldbedissolvedinthecorrespondingacidoralkalisolution.
4.hydrolysisshouldbeconsideredwhenpreparingcertainsalts
Al2S3,MGS,Mg3N2andothersubstancesareveryeasytointeractwithwater.Theycannotexiststablyinsolution.Therefore,theycannotbepreparedbythemethodofdoubledecompositionreaction,butcanonlybepreparedbydryprocess.
5.certainreactivemetalsreactwithstronglyacidweakbasesandconsiderhydrolysis
ReactivemetalssuchasMg,Al,Zn,etc.reactwithNH4Cl,CuSO4,AlCl3andothersolutions
3mg+2alcl3+6h2o=3mgcl2+2al(OH):
+3h2=3
6.todeterminetheacidityandbasicityofthesolutionattheendoftheneutralizationtitration,toselecttheindicatorandtojudgetheexcessoftheacidorbaseintheph=7,thehydrolysisofthesaltshallbetakenintoaccount
IfCH3COOHandNaOHreactexactlywhenph>7,ifthetwoisph=7afterreaction,thenCH3COOHisexcessive.
ThegeneralprincipleofindicatorselectionisthattherangeofdiscolorationoftheselectedindicatorshouldbeconsistentwiththerangeofpHvaluesofthesaltsolutionobtainedaftertitration.Thestrongandweakinteractionshouldchoosedropsofmethylorange;weakacidandalkalidropsofphenolphthaleinshouldchooseeachother.
7.preparationofferrichydroxidecolloidtoconsiderwhenhydrolysis.
Fecl3+3h2o=fe(OH)3(colloidal)+3hcl
8.hydrolysisshouldbeconsideredwhenanalyzingthereactionbetweensaltandsalt.
Thereactionoftwosaltsolutionsshouldbeconsideredinthreesteps:
(1)redoxreactionsoccur;
(2)whetherdoublehydrolysisreactioncanoccur;
(3)theabovetworeactionsdonotoccur,andthenconsiderthepossibilityofmetathesis
9.whenheating,evaporatingandconcentratingthesaltsolution,thehydrolysisofthesaltshallbetakenintoaccountindeterminingthefinalresidue
(1)whenheatingandconcentratingnonhydrolyticsaltsolution,therawmaterialisusuallyobtained
(2)heatingconcentratedNa2CO3typesaltsolution,usuallygettherawmaterial
(3)heatingandconcentratingtheFeCl3typesaltsolution.Finally,amixtureofFeCl3andFe(OH)3wasobtained,andtheFe2O3wasburned.
(4)nosolidcanbeobtainedwhenheated,evaporated,dried(NH4),2CO3orNH4HCO3salts
(5)Ca(HCO3)heatingdrysaltsolutiontype2,thecorrespondingnormalsalt.
(6)heatingMg(HCO3)2,MgCO3solution,andfinallyobtainingMg(OH)2solid
10.otheraspects
(1)thechoiceofwaterpurifyingagent:
suchasal3+,FeCl3,etc.,canbeusedaswaterpurifyingagent,shouldbeexplainedfromtheangleofhydrolysis.
(2)theuseoffertilizershallbeconsideredhydrolysis.Suchasplantashcannotbemixedwithammoniumnitrogenfertilizer.
(3)sodiumbicarbonatetabletscantreatexcessivegastricacid.
(4)sodaliquidcanbeusedtowashoilpollution.
(5)grindingreagentbottlescannotcontainNa2SiO3,Na2CO3andotherreagents
Allthisisnotalift.Inthestudy,weshouldanalyzetheconcretesituationandapplyitflexibly.
Completeflamereaction:
1.sodiumion:
Sodiumflamereactionshouldnotbedifficulttodothis,butthemosttroublesometodo.Becausesodiumflameisyellow,andthealcohollampflameforlampwickisnotclean,impurealcoholmostoftheflameisyellow.Eventhenearcolorless(paleblue)flames,anewwire(ornickelwire,platinumwire)ontheignition,thebeginningoftheflameisyellow,itisdifficulttoexplaintheflameisthesodiumionortheoriginalalcohollampflame.Toseetheyellowflameofsodiumclearly,thefollowingmethodcanbeused.
Themethod(tweezerscottonalcoholmethod):
usetweezerstotakeasmallgroupofcotton(cotton,
Alittlealcohol(95%ethanol,thesamebelow)isusedtosqueezethealcoholoutofthecotton
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