Chemical knowledge inductiontheoretical part.docx

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