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