高中化学解题方法与技巧High school chemistry problem solving methods and skills.docx

高中化学解题方法与技巧High school chemistry problem solving methods and skills.docx

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高中化学解题方法与技巧Highschoolchemistryproblemsolvingmethodsandskills

高中化学解题方法与技巧（Highschoolchemistryproblemsolvingmethodsandskills）

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Highschoolchemistryproblemsolvingmethodandskillrelationmethod

Continuousreactionsformultistepreactions

Althougheverystepofthereactionareindependent（reactionconditionsandequipmentmaybedifferent）,buttheproductbeforeareactionisareactionafterthereaction,accordingtothetransferoftheintermediateproducts,findouttherelationofrawmaterialsandfinalproducts

Itisveryconvenienttocalculatebyrelationalformula

Andtheaccuracyofthecalculationresultscanbeguaranteed

Whenlookingforarelationship,payspecialattentiontowhethersomeoftheelementsinthematerialaretransferredintotheproduct

Areintermediatesinvolvedinrawmaterial?

Itisimpossibletoblindlyderivetherelationaccordingtotheconservationofatomsintheinitialandtheproduct

Thefollowingisaconsiderableamountoftreatment:

（1）thelossrateofanelementinthecompound=thelossrateofthecompound;thelossrateoftheintermediateproduct=thelossrateoftherawmaterial;andtheintermediateproductconversionrate=theconversionrateoftherawmaterial

Thecommonreactionsofmultistepreactionsareasfollows:

1.Industrialsulphuricacid:

FeS2-2S-2H2SO4;II.Industrialsyntheticammonia:

3C-2N2-4NH3;3.Industrialnitricacid:

N2-2NH3-2HNO3;cokeacetylene;3C-CaC2-C2H2

inaddition

Insomesubjects,chemicalreactionequationsthatarenotseeninsometextbooksareoftenpresent

Intheformofinformationasasolutiontocertainconditions

Atthispoint,lookpatientlyforthetransformationbetweensubstancesorelements

Soastogetthecorrectrelation

Exercises

1,theproductionofsulfuricacidwithpyritecontainingFeS280%

Itisknownthattheorehasacombustionrateof95%

TheconversionrateofSO2was90%

TheabsorptionrateofSO3was98%

98%tonsofsulphuricacid,500tons

Howmanytonsofraworeareneeded?

Howmanylitersundertheconditionoftheair?

（assumingthevolumefractionofoxygeninairis20%）

2,industrialproductionofcalciumcarbideistouselimeandcokeheatinginthefurnace（3C+CaO==CaC2+CO）,assumingthattheutilizationrateofrawmaterials100%,then36tonsofcokecanproducetonsofacetylene?

3、chromiumcontentinsteelsampleisabout1.3%

TheprocedurefordeterminingchromiumcontentinsteelsamplesistodissolvethesteelsampleunderacidicconditionsandoxidizethechromiumtoCr2O72-ions

ThenaddthestandardFeSO4solutionof20.0mL0.100mol/L

Respondadequately

Thechemicalequationis6Fe2++Cr2O72-+14H+=6Fe3++2Cr3++7H2O,titratedwithan0.010mol/LstandardKMnO4solutiontoexcessFe2+

TheamountofKMnO4solutionrequiredisbetween5.00~10.00mL

Calculatetherangeofthesteelsample

（PotassiumPermanganateandionicequationforthereactionofFe2+:

5Fe2++MnO4-+8H+=5Fe3++Mn2++4H2O）

4.TodeterminethemassfractionofCaCO3inalimestone

WeighWglimestonesamples

Addanexcessof6mol/Lhydrochloricacid

Dissolveitcompletely

Heatboiling

RemovedissolvedCO2

Thenaddsufficientquantitiesofammoniumoxalate[（NH4）C2O4]solution,slowlyaddingammoniareducestheacidityofthesolution,whiletheprecipitationofcalciumoxalateprecipitation:

C2O42-+Ca2+=CaC2O4down,filteroutCaC2O4,H2SO4:

CaC2O4+H2SO4=H2C2O4+CaSO4,dissolvedasdilutedwithdistilledwaterdilutesolutiontoremoveV0mL,V1mL,KMnO4inacidsolutiontitrationofamol/Loccursatthistimethefollowingreaction:

__MnO4-+__H2C2O4+__H+,___Mn2++___CO2=+__H2Oiftheendpointoftitrationconsumptionduringamol/LKMnO4V2mL,pleaseKMnO4thetrimionequationandH2C2O4reaction,andcalculatethemassfractionofCaCO3inthesample.

5.Thereactionofphenolandbrominecanbeusedforthequantitativedeterminationofphenol

Themethodisasfollows:

1.KBrO3-KBrsolution1000mLispreparedbytheratioofmaterialto1:

5

Thesolutionreactscompletelyunderacidicconditionstoproduce0.05molBr2;thereactionisfollowedbythereactionofthesolutionwithanexcessofBr2

ReductiveunreactedbromidewasreducedwithKI

TitratetheiodineproducedwiththeNa2S2O3standardsolution

ThechemicalequationforthereactionofNa2S2O3withI2is2Na2S2O3+I2=2NaI+Na2S4O6;accordingtothevolumeoftheNa2S2O3standardsolutionconsumed

Thepurityofphenolcanbecalculated

Weighing0.2gphenolsample

Dissolveinwateranddiluteto250mLundercertainconditions

Takethesolution10mL

TheaboveKBrO3-KBrsolutionreactswiththe10mLunderacidicconditions

AddexcessKI

Titratewith0.1mol/LNa2S2O3solutiontothefinishline

ConsumeNa2S2O3solution,5.2mL

Calculatethepurityofphenolsample

（phenoltype94）

Solvingmethodsandskillsinhighschoolchemistry-totalresponseequationmethod

Amongtheproblemsinchemistrycalculationinseniorhighschool,therearesometypesofproductcategoriesthatvarywiththeamountofreactants

SuchasH2S+O2

WhenO2isnotenough

TheVO2/VH2Sislessthanorequalto1/2

2H2S+O2=2S+2H2O;whenO2isenough

VO2/VH2Sismorethanorequalto3/2

2H2S+3O2=2SO2+2H2O;andwhen1/2

TheproductsofH2ScombustionarebothSandSO2.Itisverycomplicatedanderrorproneiftheyarediscussedstepbystepaccordingtoeachspecificreaction

Atthispoint,thetotalreactionequationcanbetrimmedbytheratiooftheamountofreactantmaterial

Thetotalresponseequationisusedtojudgeandcalculatedirectly

Similarreactionsinclude:

CO2+NaOH=OH,CO2+Ca

（2）,H3PO4+NaOH,H3PO4+NH3,Na2CO3+HCl,Al3++NaOH,AlO2-+H++H2O,Fe+HNO3,etc.

Exercises

At1and20degreescentigrade

Mix40mlH2Swith50mlO2andignite

Howmanymillilitersofgasarethereafterreaction?

（setthetemperatureandpressureunchanged）

2,thestandardconditionsof1.12litersofCO2gasinto100ml0.7mol/literofcausticsodasolution,andthenatlowtemperaturevacuumevaporationdryingsolution,howmanygramsofsolidcanget?

3,200mL0.8mol/Lhydrochloricaciddropsintothe300mL0.4mol/LNa2CO3solution

Aftercompletereaction

CalculatethevolumeoftheresultingCO2inthestandardcase

4,to148gconcentrationof0.1%clearlimewaterthroughCO2gas

Getwhiteprecipitate0.1g

IfCO2takesfulladvantageof

ThevolumeoftheCO2gaspassedintois（）

A.22.4mLB.33.6mLC.44.8mLD.67.2mL

5.AbsorbNH3under11.2Lstandardwith2mol/LH3PO4solution200mL

Fullacting

Whatistheproduct?

Whatistheamountofitssubstance?

6,AgironreactsexactlywithnitricacidwithBGnitricacidtoformNO

Ifa:

b=1:

3

Thequalityofthereducednitricacidis（）

A.agB.3a/4gC.b/4gD.bg

7,in100ml0.1mol/LAlCl3solution,intothemetalsodium,tobecompletedafterthereactionH2392ml（superscriptcase）,ifthemetalsodiumsurfaceisnotoxidized,canproduceprecipitationhowmanygrams?

8,understandardconditions

AmixtureofCOandCO2isfilledwithavolumeof22.4L,andasufficientamountofairtightcontainerisusedtoinitiateacompletereactionwithainterruptedelectricalspark

Thefollowingarethecorrectestimatesoftheamountofsubstancesandtheirsubstancesthatarepresentinthecontainer（excludingthevolumeoccupiedbythesolidmaterial）

A.exists,0.5molNa2CO3,0.25molCO,B.exists,0.125molO2,1mol,Na2CO3

C.exists0.5molCO,0.5molNa2CO3,D.exist0.75molNa2CO3,0.25molCO

9.MixtheamolNa2O2andbmolNaHCO3solidsandheatthemto250degreesinaclosedvessel

Theexhaustgasafterfullreaction（setonlywhentheCO2andNa2O2afterreaction,othersubstancesthatreactwithNa2O2）,ifthereactionpressurecontaineris0Pa,andthesolidresidueinwatersolutionwithoutgas,thenaddproperamountofCH4inthereaction,sothatitcanbefullyburnt.Thisa/bshouldsatisfywhatconditions?

JoinCH4instandardconditionofthevolumeishowmuch?

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2002collegeentranceexaminationtrainingquestions:

chemicalcalculation