2019 final exam fall answers explained · 2019 final exam (gardner version) with explanations and...

2019FinalExam(GardnerVersion)withExplanationsandAnswers

Choosethebestanswertoeachofthefollowingquestions.

1. Whatisthemolarityofasolutioninwhich15.0gramsofNaClhasbeendissolvedin2.375litersofwater?a. 0.108Mb. 0.257Mc. 6.32Md. 12.6M

Remember,Molarityiscalculatedinmoles/liters.Manyofyoujustdividedthegramsbytheliters—butyoucan’tdothat!Payattention!Ifyouaregivengrams,youhavetoconvertthemtomolesandthendividebyliters.15.0gramsNaClx1moleNaCl/58.44g(molarmass)/2.375liters=0.108M

2. Whichcoefficientswillbalancetheequationbelow?_____Ca(ClO3)2à_____CaCl2+_____O2

a. 1,1,2b. 1,1,3c. 1,2,3d. 2,2,3

Atthebeginning,ontheleft,thereare1Calcium,2Chlorines,and6Oxygens.Ontheright,thereare1Calcium,2Chlorines,and2Oxygens.TheonlythingoutofbalanceisOxygen,sowejustneedtosticka3infrontoftheO2tobalance.

3. Lookatthegraphontheright.Findthestar.Whichprocessoccursatthatpartofthegraphifpotentialenergyisbeingabsorbed?a. Meltingb. Freezingc. Condensationd. Vaporization

Remembertheflatpartsofthegraphareareaswheretemperaturedoesn’tchange.Theyrepresentprocesses,notphases.Thediagonalsfromthebottomaresolid,thenliquid,thengas.IfweareABSORBINGenergy,heatisbeingadded,sothebottomflatlinerepresentsmelting.Thetopflatlinewherethestarisrepresentsboilingorvaporization.

4. Whichelementsareinthesameperiod?a. Lithium,Hydrogen,Sodiumb. Nitrogen,Oxygen,Fluorinec. Neon,Bromine,Phosphorusd. Uranium,Cesium,Krypton

Periodsarethehorizontalrowsontheperiodictable.Soyou’rejustlookingforthreeelementsthatareonthesamerow.

5. Whichistrueaboutatoms?a. Thenucleusofanatomisfilledwithprotons,neutrons,andelectrons.b. Mostofthevolumeofanatomisfilledwithemptyspace.c. Allatomswillacceptelectronstobecomeions.d. Thenucleiofatomsarealwaysneutralincharge.

Thenucleusofatomsonlycontainsprotonsandneutrons.Mostoftheatom’svolumeisEMPTYSPACE.Metalswon’tacceptelectrons,theyjustgivethemaway.Thenucleiofatomsarealwayspositive(becauseprotons(+)andneutrons(o)aretheonlythinginside).

6. WhatisthenameofthechemicalHNO3?a. hydrogennitrateb. hydrogennitritec. nitricacidd. nitrousacid

Remember,withtheexceptionofwater(H2O)andhydrogenperoxide(H2O2),everychemicalthathasaformulastartingwithHisanacid.Polyatomicionsthatendin–atebecome–icacids,andpolyatomicionsthatendin–iteare–ousacids.

7. Lookattheequationbelowanddeterminewhichstresswouldshifttheequilibriumofthereversiblereactionstowardtheproducts?

8SO2(g)ßàS8(g)+8O2(g)+1200kJa. Pressureisincreased.b. Temperatureisincreased.c. Sulfurisadded.d. O2leaksfromthereaction.

Stressaffectsequilibrium(LeChatelier’sprinciple).Ifpressureisincreased,onlygasesmatterandyoushifttheequationfromhighmolesofgastowardlowmolesofgas.Thereare8molesofgasontheleftand9molesofgasontheright,sotheshiftwouldbetotheleft(reactants).Iftemperatureisincreased,thenthesidethathasenergywillhavetoomuchandtheequationwillshiftawayfromtheenergy.Energyisontheright,sothereactantswillbefavored(leftshift).Ifsulfurisadded,thereistoomuchsulfurontheright,soitwillshiftleft.But,ifoxygenleaks,thenthereisaholeontheright,andtheequationwillshiftrighttomakeupfortheloss.

8. Twochemicalsaremixedtogether.Alitmatchisbroughtnearthemouthofthetesttubeandtheflameflaresexplosivelyandmakesaloudwhistlingpop!Whichgaswasmostlikelygeneratedbythereaction?a. Hydrogenb. Nitrogenc. Watervapord. Carbondioxide

Hydrogenisflammable/explosive.Aroundaflame,you’llgetaflashandpop!Nitrogen,watervapor,andcarbondioxideareallanti-burnerssothematchwouldbeextinguished.

9. Whichreactionismostlikelytooccur?a. 2Na+2H2Oà2NaOH+H2b. Cd+MgOàCdO+Mgc. Ni+ZnCl2àNiCl2+Znd. 2Fe+3CaCl2à2FeCl3+3Ca

Remember,insinglereplacementreactions,youmustlookattheActivitySeriesinyourReferenceTables.IfthesingleelementishigherontheActivitySeriesthantheelementinthecompound,thereactionwilloccur.ThatonlyhappenswithNareplacingtheHinwater.CdwillnotreplaceMg.NiwillnotreplaceZn.FewillnotreplaceCa.

10. Whichwouldmostlikelyincreasetherateofreaction?a. Decreasethetemperatureb. Increasethevolumeofthecontainerc. Increasethesurfaceareaofsolidreactantsd. Increasetheactivationenergy

Toincreasetherateofreaction,weneedmorecollisionsbetweenmolecules.Collisionsincreasewhentemp.isincreased,whentherearemoreparticlestocrashintoeachother,orwhentheparticlesinagasarebroughtclosertogether.Decreasingthetemp.wouldslowdownparticlesandstopcollisions.Increasingthevolumewouldmakemoreroomandtheparticleswouldbelesslikelytohiteachother.Increasingthesurfaceareawouldmakemoreparticlesavailabletocrashintoeachother.IncreasingtheactivationenergywouldmakeitHARDERtoreactbecausemoreenergywouldberequiredforthereaction.

11. Whichbestdescribesthesubatomicparticlesin210Pb2+?a. 82protons,125neutrons,80electronsb. 82protons,125neutrons,82electronsc. 82protons,128neutrons,80electronsd. 82protons,128neutrons,84electrons

Pb(Lead)has82protonsaccordingtothePT.Themassnumberforthisisotopeis210,so210-82=128neutrons.Becausethisionhasa2+charge,thereshouldbe2lesselectronsthanprotons(82-2=80electrons).

12. UsingtheBohrModelofHydrogen,whatkindofenergyisemittedwhenanelectronmovesfromn=5ton=3?a. Visiblelight,blueb. Visiblelight,redc. Ultravioletradiationd. Infraredradiation

Anyelectronmovingtowarditsgroundstateton=3wouldreleaseinfraredradiation.

13. Whichcompoundisapolarcovalentcompound?a. NaClb. CH4c. CO2d. NH3

CovalentcompoundsaremadeofONLYNONMETALS.NaClisIONICbecauseitcontainsametal(Na).CH4andCO2arebothcovalentcompounds,butbecausetheysharetheirelectronsequally,theyarenonpolar.NH3hasarelativelynegativelychargedendandarelativelypositiveendbecauseofunequallysharedelectrons.

14. Basedontheelectronconfigurationofanatom,1s22s22p63s23p4,whichstatementistrueabouttheatomasitbecomesanion?a. Theelementislikelytogain2electronstobecomeanion.b. Theelementislikelytolose2electronstobecomeanion.c. Theelementislikelytogain4electronstobecomeanion.d. Theelementislikelytolose4electronstobecomeanion.

Rememberwithelectronconfiguration,thenumbersinfrontoftheletterstellyouwhatring(energylevel)electronsareon.Thelargestnumberinfrontofthelettersis3,sothevalence(outside)ringis#3.Onthethirdenergylevel,wehave2electronsfromthes,and4fromthep,foratotalof6valenceelectrons.Weneed8electronstobestable.So,thiselementmuchpickup2electronstobecomeanion.

15. Howmuchenergymustbeabsorbedbyapieceoficethathasamassof38gramsinordertomelttheice?a. 13000Jb. 26000Jc. 86000Jd. 180000J

ThisquestionisONLYaskingyouabouttheenergyneededtomelttheice.Temperaturedidnotchangeduringthisprocess.So,weuseashortQequation.Becausewearemelting,wemustuseheatoffusion(HF).Q=mHfTheheatoffusionofwateris334J/g.Soweonlyhavetosaymass(38)xHf(334).Thatgives12,692,whichin2SigFigsis13000J.

16. 17.5Lofgasinaballoonareunderapressureof1.23atm.Ifthepressureisincreasedto2.88atm,thenwhatisthenewvolumeofthegas?a. 5.41Lb. 7.47Lc. 9.13Ld. 12.7L

Thisgaslawonlyusesvolumeandpressure.UseBoyle’sLawP1V1=P2V2tosolveforV2.1.23x17.5=2.88xV2à(1.23x17.5)/2.88=V2àV2=7.47L

17. Whichreactionwillproduceaprecipitate?a. NaNO3+KClà?b. LiF+HC2H3O2à?c. MgCl2+Na2Oà?d. Al(NO3)3+CaBr2à?

Forthisproblem,youhavetocompletethedoublereplacementreactiontofindtheproducts.Then,youhavetousethesolubilitychartonyourReferencetabletofigureoutwhichproductisnotsoluble.OxidesareNOTsolubleunlesstheyaremadewithGroup1metals.OneoftheproductsofC.(MgO)isinsolubleandthereforeaprecipitate.

18. Whichcompoundhasthegreatestpercentofoxygenbymass?a. Li2Ob. MgOc. H2Od. Zn(NO3)2

Findthemolarmassofeachofthefourcompounds.Then,dividetheamountofoxygenineachonebythemolarmassforeachone.

19. WhatisthepHofachemicalthathas[H+]=1x10-8M?a. 1b. 6c. 8d. 10

Remember,pHisalogarithmicscale.Ifyoureallywanttoputthisintothecalculator,enter–log[1x10-8]andyouwillget8.OR,iftheformatiseasylike1x10n,thepH=n.

20. Whichchemicalwouldmostlikelybecomeanelectrolytewhendissolvedinwater?a. Sucrose(C12H22O11)b. Carbondioxide(CO2)c. Tablesalt(NaCl)d. Sulfurtrioxide(SO3)

Ioniccompoundsalwaysmakeelectrolytesinsolutions.Covalentcompoundsarenonelectrolytes.Theonlyioniccompoundonthislististablesalt.

21. Lookatthesolubilitycurvesontheright.HowmuchKNO3wouldittaketosaturateasolutionmadewith200gramsofwaterat30degreesCelsius?a. 35gramsb. 45gramsc. 70gramsd. 90grams

Thesolubilitycurvegraphisbasedon100gH2O.Ifyoulookatthegraph,youseeKNO3at30degreesC,itissaturatedat45grams—whichiswhatmostofyouchose.BUT,thequestionaskedabout200gramsofwater.So,if45gramswillbedissolvedin100gramsofwater,then90gramswillbedissolvedin200gramsofwaterbecauseyouhavedoublethesolute.

22. Stillusingthesolubilitycurvesontheright,howcouldyoudescribethesolutionthatformedif12gramsofKClO3weredissolvedin100gramsofwaterat20degreesC?a. Saturatedb. Unsaturatedc. Supersaturatedd. Dilute

WhenyoulookatwhereKClO3isat20degreesC,about8gramsofsolutecanbedissolved.If12gramshavebeendissolved,thatisOVERtheline,sothesolutionisSUPERsaturated.

23. Whichparticlewouldfilltheblanktomakethefollowingnuclearreactionmakesense?

14Cà14N+_____a. Alphaparticleb. Betaparticlec. Gammaradiationd. Positron

Ifwefillinthemissinginformationintheequation,theleftsidehasamassof12,andatomicnumberof6.Ontheright,wehaveamassof12andanatomicnumberof7.Ifwethensolveforxandyinthetwoequations,6=6+x,sox=0.6=7+y,soy=-1.Soourblankhasamassof0andanatomicnumberof-1.Thatdescribesanelectron,whichisalsoknownasabetaparticle.(Alphaparticlesare4and2,Gammais0and0.Positronsare0and1).

24. Whichtypeofbondismostoftendescribedasa“seaofelectrons”thatformsaroundapositivesetofnuclei?a. Ionicb. Covalentc. Metallicd. Hydrogen

“Seaofelectrons”istheliteraldefinitionofmetallicbonds.

25. Whichtypeofbondismostlikelytobeaweakbondbetweentwodifferentmolecules,ratherthanabondthatholdsatomstogethertoformonemolecule?a. Ionicb. Covalentc. Metallicd. Hydrogen

IonicandCovalentbondsarebondsbetweenatoms,notmolecules,andarestronger.Metallicbondsareauniquekindofbondthatdoesn’tholdmoleculestogethereither.Hydrogenbondsholddifferentmolecules(likewater)together,butareweak.Breakingthehydrogenbondsofwatercausesthephasetochangebetweenice,liquid,andsteam.

26. Whichchemicalismostlikelytobeconsideredanacid?

a. Soapb. Vinegarc. Waterd. Bakingsoda

Cleanersareusuallybases.Waterisneutral.Acidsareusuallysourtothetaste,likevinegar.

27. Forasetofreversiblereactionstobeatequilibrium,the_____mustbethesame.a. Concentrationsofreactantsb. Concentrationsofproductsc. Ratesofreactionsd. Massesofproductsandreactants

Thedefinitionofequilibriumis:Reversiblereactionsoccuratthesamerates.

28. Usingthereversiblereactionsbelow,whatisthecorrectequilibriumexpressionforcalculatingtheequilibriumconstant?

2NH3(g)ßàN2(g)+3H2(g)a. [NH3]/[N2][H2]b. [NH3]2/[N2][H2]3c. [N2][H2]3/[NH3]2d. [N2][H2]/[NH3]

Tocalculatetheequilibriumconstant,[products]coefficient/[reactants]coefficients

29. Usingtheequationintheproblemabove,ifyouhad6.0molesofNH3,howmanymolesofH2gaswouldbeproducedfromthedecomposition?a. 3.0b. 6.0c. 12d. 18

YouguyswereallgivencreditforthisproblembecauseIwasstupidandthecorrectanswerisn’tanyofthesechoices.Theactualanswerisfoundbystoichiometry:6.0molesNH3x3.0molesH2/2.0molesNH3=9.0molesH2

30. Accordingtothecollisiontheory,toincreasetherateofreactions,youmust:a. Increasethenumberofcollisionsb. Decreasethenumberofcollisionsc. Increasetheactivationenergyd. Decreasetheaveragekineticenergyoftheparticles

Morecollisions=morereactions!INCREASINGACTIVATIONENERGYISNOTGOOD.THATMAKESITHARDERFORAREACTIONTOOCCUR.

31. Whichphrasebestdescribestemperatureofasubstance?a. Averagekineticenergyoftheparticlesb. Averagepotentialenergyoftheparticlesc. Amountofheatemittedbyparticlesd. Amountofheatabsorbedbyparticles

Thedefinitionoftemperatureisaveragekineticenergyoftheparticlesofasubstance.

32. WhichprocessoccursifthesubstanceatPointXchangedconditionsasindicatedinthegraph?a. Meltingb. Sublimationc. Depositiond. Vaporization

PointXisaSOLID.IfitcrossesthelineanddirectlybecomesaGASwithoutbecomingaliquidfirst,thatissublimation.

33. Basedonthephasechart,whatistrueat510.2kPaand216.8K?a. Thesubstanceexistsinallthreephases.b. Thesubstanceisvaporizing.c. Thesubstanceismelting.d. Thesubstanceisatthecriticalpoint.

Thosecoordinatesshowthepointwhereallthreephasesunite(triplepoint).Becauseoftheconnectionbetweenallthreephases,anyofthemorallofthemcanexistatthattempandpressure.

X

34. Na2SO4isdroppedintowaterwhereitdissolves.Whichcorrectlyexplainswhathappensbetweenthesoluteandsolvent?a. ThepositiveO-endofthewatermoleculeseparatesandsurroundstheNa+of

thesalt.b. ThenegativeO-endofthewatermoleculeseparatesandsurroundstheNa+

ofthesalt.c. ThepositiveO-endofthewatermoleculeseparatesandsurroundstheSO42-

ionofthesalt.d. ThenegativeO-endofthewatermoleculeseparatesandsurroundstheSO42-

ionofthesalt.Inthesolution,Na2SO4willsplitintoions(Na+andSO42-).Becauseoppositesattract,negativethingswillbeattractedtotheNa+andsurroundit.TheO-endofthewatermoleculeisrelativelynegative(polar).PositivethingswouldbeattractedtoSO42-sotheHydrogenendofthewatermoleculewouldbeattractedtothesulfateandsurroundit.

35. 2800JoulesofenergyarereleasedfromabarofIronasitcooleddownfrom96.2degreesCto18.1degreesC.Whatwasthemassoftheironbar?a. 80.gramsb. 120gramsc. 150gramsd. 230grams

ThelongQequationisneededtosolvethisproblem.Q=mx(TF–TI)xCp-2800=m(18.1–96.2)0.449,solveform;m=80grams

36. WhichisthecorrectformulaforthecompoundthatwouldformbetweenelementsYandZbasedontheirLewisDotStructures?a. YZ2b. Y2Zc. Y2Z3d. Y3Z2

TheLewisdotstructuresrepresentacationandanion.Y3+andZ2-.Ifyoujustswapanddrop,yougettheanswer.

37. Whichelementfromthislistismostelectronegative?a. Nitrogenb. Fluorinec. Nickeld. Francium

Remember,notcountingtheNobleGases,electronegativityincreasesaswemovefromlefttorightacrossthePTandfrombottomtotop.Nonmetalsaremoreelectronegativethanmetalsbecausetheywanttotakeelectrons,metalsdon’t.Fluorineisthemostelectronegative.

Y Z

38. Whichisas-blockelementinthefifthperiod?

a. Kb. Src. Snd. Pb

Rememberthes-blockelementsarethefirsttwocolumnsofthePT.Thefifthperiodisthe5throw.Kiss-block,butnot5thperiod.Snisd-blockandPbisp-block.

39. Whichwouldresultinmorecollisionsbetweenmoleculesinasolution?a. Preventingthesolutionfrommovingb. Increasingthepressureonthesolutionc. Loweringthetemperatureofthesolutiond. Stirringthesolution

Ifthesolutiondoesn’tmove,nocollisionswilloccur,thusnoreaction.Ifyouincreasethepressure,itwouldhavenoeffect,becausethesolutionisliquidandpressureonlyaffectsgasparticles.Loweringthetempwouldslowparticlesdown,reducingcollisions.Stirringthesolutionwillspeedparticlesupandmakemorecollisionsoccur.

40. Whichistrueaboutasolutionwith[OH-]=7.00x10-9M?a. IthasapHof8.15andisabase.b. IthasapHof8.15andisanacid.c. IthasapHof5.85andisabase.d. IthasapHof5.85andisanacid.

Youaregivenahydroxideconcentration[OH-].First,youneedtousetheequation:-log[7.00x10-9]andthatwillgiveyouthepOHof8.15,NOTapHof8.15.YouneedtosubtractpOHfrom14tofindthepH.14-8.15=5.85ThepHis5.85—thatislessthan7,sothechemicalisanACID.

41. Whichelementwouldmostlikelyformacation?a. Neon b. Chlorine c. Potassium d. Nitrogen

Cationsarepositivelychargedions.Onlymetalsmakecationsbecausetheygiveawayelectrons.Anionsarenegativelychargedions.

42. WhichisthenameofthecompoundP2O5?a. Phosphorusoxideb. Phosphorusmonoxidec. Diphosphorusmonoxided. Diphosphoruspentaoxide

Everyonegotthisquestioncorrect.I’mgladyourecognizehowtonamecovalentcompoundsusingprefixes.

43. Whichofthesubatomicparticlesisthesmallest?

a. Protonb. Neutronc. Electrond. Nucleus

Protonsandneutronsarethesamesize.Theyare1a.m.u.(atomicmassunit).Thenucleusholdsthemsoit’sbigger.Theelectronsare1/2000thesizeofaprotonorneutron,whichiswhywedon’tincludetheminthemassnumber.

44. Lookatthereactionontheright.Whatstatementistrue,basedonthegraph?a. Itisexothermic.b. Itisendothermic.c. Itisadecompositionreaction.d. Itisacombustionreaction.

Thereactantshavemuchlessenergythantheproducts.Soenergymust’vebeenabsorbedbythereaction.Whenenergyisabsorbed,thereactionisendothermic.

45. Whichhydrateismadeofmorethan50%water?a. Na2CO3*10H2Ob. FeSO4*7H2Oc. Ba(OH)2*8H2Od. NaC2H3O2*3H2O

Findthemolarmassofeachofthehydrates.Then,dividetheamountofwaterbythemolarmassofthewholehydrate.

46. Howmanymolesofnitrogengasarepresentin18.1Latatemperatureof350Kandapressureof787mmHg?a. 0.65molesb. 0.85molesc. 1.2molesd. 1.5moles

Thisproblemcanbesolvedusingtheidealgaslaw.PV=nRT787x18.1=n(62.4)350,solveforn.*The62.4camefromthereferencetable(gasconstant)

47. Whichpairofelementsismostlikelytoshareelectronswhenbonding?a. Ironandchlorineb. Sulfurandfluorinec. Neonandnitrogend. Sodiumandmagnesium

Covalentbondsformwhenelectronsareshared.Covalentbondsformbetweennonmetalsonly.Noblegaseswon’tmakecompounds.

48. WhichVSEPRshapeisdemonstratedbythemoleculeontheright,CH4?a. Bentb. Linearc. Tetrahedrald. Trigonalpyramid

4atomsarespreadevenlyaroundacentralatom.Thatshapeisanisohedronakatetrahedral.

49. Lookattheequationbelow.DeterminehowmanygramsofC4H10mustbecombustedinordertorelease7.6x1024m/cofCO2.

2C4H10+13O2à8CO2+10H2Oa. 180gramsb. 210gramsc. 340gramsd. 410grams

7.6x1024m/cCO2x1moleCO2/6.02x1023m/sCO2x2molC4H10/8molCO2x58g=183gramsà2SigFigs:180g.

50. Whichtwofactorshavethegreatestinfluenceoverthephaseofasubstance?a. Massandpressureb. Pressureandtemperaturec. Temperatureandvolumed. Volumeandmass

Thinkaboutthephasechangechart,thevariablesonthechartaretempandpressure.

51. Youhave200gramsofU-235.Ifthehalf-lifeoftheradioisotopeis4.5billionyears,howmuchwouldbeleftafter18billionyears?a. 100grams b. 50grams c. 25grams d. 12.5grams

18billionyears/4.5billionyears=4half-lives200à100à50à25à12.5