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AP CHEMISTRY
Composition and Reaction Stoichiometry
Presenter Name: ______________________________Please write down the name of the presenter for this session.You will need the title of the session and presenter's name forevery session you attend to complete the survey you will bereceiving by email later today.If you complete the survey by Tuesday morning, you will beentered for a chance to win a $25 Amazon gift card!
47.9
0
91.2
2
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49
(261
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50.9
4
92.9
1
180.
95
(262
)
52.0
0
93.9
4
183.
85
(263
)
54.9
38
(98)
186.
21
(262
)
55.8
5
101.
1
190.
2
(265
)
58.9
3
102.
91
192.
2
(266
)
H Li Na K Rb
Cs Fr
He
Ne Ar
Kr
Xe
Rn
Ce
Th
Pr
Pa
Nd U
Pm Np
Sm Pu
Eu
Am
Gd
Cm
Tb Bk
Dy Cf
Ho
Es
Er
Fm
Tm Md
Yb
No
Lu Lr
1 3 11 19 37 55 87
2 10 18 36 54 86
Be
Mg
Ca Sr
Ba
Ra
B Al
Ga In Tl
C Si
Ge
Sn
Pb
N P As
Sb Bi
O S Se Te Po
F Cl
Br I At
Sc Y La Ac
Ti Zr Hf
Rf
V Nb Ta Db
Cr
Mo W Sg
Mn Tc Re
Bh
Fe Ru
Os
Hs
Co
Rh Ir Mt
Ni
Pd Pt §
Cu
Ag
Au §
Zn Cd
Hg §
1.00
79
6.94
1
22.9
9
39.1
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7
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91
(223
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12
232.
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237.
05
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4
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151.
97
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157.
25
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158.
93
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162.
50
(251
)
164.
93
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167.
26
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168.
93
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173.
04
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174.
97
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9.01
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8
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11
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98
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78.9
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60
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91
(210
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58.6
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08
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63.5
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87
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97
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65.3
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59
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4 12 20 38 56 88
5 13 31 49 81
6 14 32 50 82
7 15 33 51 83
8 16 34 52 84
9 17 35 53 85
21 39 57 89
58 90
*Lan
than
ide
Ser
ies:
†Act
inid
e S
erie
s:
* †
59 91
60 92
61 93
62 94
63 95
64 96
65 97
66 98
67 99
68 100
69 101
70 102
71 103
22 40 72 104
23 41 73 105
24 42 74 106
25 43 75 107
26 44 76 108
27 45 77 109
28 46 78 110
29 47 79 111
30 48 80 112
Perio
dic
Tabl
e of
the
Elem
ents
§Not
yet
nam
ed
ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS
Throughout the test the following symbols have the definitions specified unless otherwise noted.
L, mL = liter(s), milliliter(s) mm Hg = millimeters of mercury g = gram(s) J, kJ = joule(s), kilojoule(s) nm = nanometer(s) V = volt(s) atm = atmosphere(s) mol = mole(s)
ATOMIC STRUCTURE
E = hν
c = λν
E = energy ν = frequency
λ = wavelength
Planck’s constant, h = 6.626 × 10−34 J s
Speed of light, c = 2.998 × 108 m s−1
Avogadro’s number = 6.022 × 1023 mol−1
Electron charge, e = −1.602 × 10−19 coulomb
EQUILIBRIUM
Kc = [C] [D]
[A] [B]
c d
a b, where a A + b B c C + d D
Kp = C
A B
( ) ( )
( ) ( )
c dD
a b
P P
P P
Ka = [H ][A ][HA]
+ -
Kb = [OH ][HB ][B]
- +
Kw = [H+][OH−] = 1.0 × 10−14 at 25°C
= Ka × Kb
pH = − log[H+] , pOH = − log[OH−]
14 = pH + pOH
pH = pKa + log [A ][HA]
-
pKa = − logKa , pKb = − logKb
Equilibrium Constants
Kc (molar concentrations)
Kp (gas pressures)
Ka (weak acid)
Kb (weak base)
Kw (water)
KINETICS
ln[A] t − ln[A]0 = − kt
[ ] [ ]0A A1 1
t
- = kt
t½ = 0.693k
k = rate constant
t = time t½ = half-life
ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS
Throughout the test the following symbols have the definitions specified unless otherwise noted.
L, mL = liter(s), milliliter(s) mm Hg = millimeters of mercuryg = gram(s) J, kJ = joule(s), kilojoule(s) nm = nanometer(s) V = volt(s)atm = atmosphere(s) mol = mole(s)
ATOMIC STRUCTURE
E = hνc = λν
E = energy ν = frequency
λ = wavelength
Planck’s constant, h = 6.626 × 10−34 J s
Speed of light, c = 2.998 × 108 m s−1
Avogadro’s number = 6.022 × 1023 mol−1
Electron charge, e = −1.602 × 10−19 coulomb
EQUILIBRIUM
Kc = [C] [D]
[A] [B]
c d
a b, where a A + b B c C + d D
Kp = C
A B
( ) ( )
( ) ( )
c dD
a b
P P
P P
Ka = [H ][A ][HA]
+ -
Kb = [OH ][HB ][B]
- +
Kw = [H+][OH−] = 1.0 × 10−14 at 25°C
= Ka × Kb
pH = − log[H+] , pOH = − log[OH−]
14 = pH + pOH
pH = pKa + log [A ][HA]
-
pKa = − logKa , pKb = − logKb
Equilibrium Constants
Kc (molar concentrations)
Kp (gas pressures)
Ka (weak acid)
Kb (weak base)
Kw (water)
KINETICS
ln[A] t − ln[A]0 = − kt
[ ] [ ]0A A1 1
t
- = kt
t½ = 0.693k
k = rate constant
t = time t½ = half-life
GASES, LIQUIDS, AND SOLUTIONS
PV = nRT
PA = Ptotal × XA, where XA = moles A
total moles
Ptotal = PA + PB + PC + . . .
n = mM
K = °C + 273
D = m
V
KE per molecule = 12
mv2
Molarity, M = moles of solute per liter of solution
A = abc
1 1
pressurevolumetemperaturenumber of molesmassmolar massdensitykinetic energyvelocityabsorbancemolarabsorptivitypath lengthconcentration
Gas constant, 8.314 J mol K
0.08206
PVTnm
DKE
Aabc
R
Ã
- -
=============
==
M
1 1
1 1
L atm mol K
62.36 L torr mol K 1 atm 760 mm Hg
760 torr
STP 0.00 C and 1.000 atm
- -
- -====
THERMOCHEMISTRY/ ELECTROCHEMISTRY
products reactants
products reactants
products reactants
ln
ff
ff
q mc T
S S S
H H H
G G G
G H T S
RT K
n F E
qI
t
D
D
D D D
D D D
D D D
=
= -Â Â
= -Â Â
= -Â Â
= -
= -
= -
�
heatmassspecific heat capacitytemperature
standard entropy
standard enthalpy
standard free energynumber of moles
standard reduction potentialcurrent (amperes)charge (coulombs)t
qmcT
S
H
Gn
EIqt
============ ime (seconds)
Faraday’s constant , 96,485 coulombs per moleof electrons1 joule
1volt1coulomb
F =
=
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NATIONALMATH + SCIENCEINITIATIVE
CompositionandReactionStoichiometryWarm-Up
1) Acompoundcontains40%calcium,12%carbon,and48%oxygen.Whatistheempiricalformulaforthecompound?(A) CaC2O4 (B)CaCO3 (C)CaCO4 (D)CaCO6
2) AcertainhydrocarbonwasfoundtohaveanempiricalformulaofCH3.Itsmolarmasswasdeterminedtobe
30.0g/mol.Whatisitsmolecularformula?(A) CH3 (B)C2H6 (C)C3H9 (D)C4H12
3) Whichofthefollowingcompoundscontainsthegreatestpercentageofiron?
(A) FeCl2 (B)FeO (C)Fe3(PO4)2 (D)Fe3O4
4) DinitrogentetroxideisformedfromitsgaseouselementsatSTP.Howmanylitersofeachreactantarerequiredtoform44.8Lofdinitrogentetroxide?(A) 22.4LN2and22.4LO2 (B)22.4LN2and44.8LO2(C)44.8LN2and22.4LO2 (D)44.8LN2and89.6LO2
5) ForareactionA+B→C,howmanylitersofCcanbeformedwhen3LofAand4LofBreactatSTP?
(A) 3LofC (B)4LofC (C)6LofC (D)7LofC
Forthese,youcanuseacalculator
6) Combustionanalysisofahydrocarbonproduced33.01gofCO2and13.51gofH2O.Determinetheempiricalformulaofthehydrocarbon.
7) A1.50gsampleofZniscombinedwith250.mLof0.110MAgNO3at25°C.IdentifythelimitingreactantanddeterminetheamountofZn2+produced.
2Ag+(aq)+Zn(s)→Zn2+(aq)+2Ag(s)
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CompositionStoichiometry• Rememberthatwhenlookingatachemicalformulathesubscriptsnotonlytellusaratioofatomsbut,more
importantly,aratioofMOLESOFATOMS.
• Empiricalformulaproblemsthenbecomeanexerciseinconvertingmasstomolesandultimatelyfindingmoleratioofelements.
• InordertogetamolecularformulayouMUSThavethemolecularmolarmass.
MMempiricalx______=MMmolecularThatfactoristhenappliedtothesubscriptsoftheempiricalformulatoproducethemolecularformula.
• Combustionanalysissimplyaddsoneadditionalstepinyourcalculation;youmustusethemassofCO2andH2OtodeterminethenumberofmolesofCandHrespectively.Rememberthatthereis1molC/1molCO2and2molH/1molH2O
• Theseproblemsarestrongcandidatesforinclusionoflaboratorydata.Beonthelookoutforthesecalculations
inlab-basedscenarios.TurnandTalk
1) WhatifavolumeofCO2wasgiveninacombustionprobleminsteadofamass?HowdoesthatchangethecalculationofmolesofC?
2) Whatifathirdelementwasincludedinthecombustionproblem–likeN,S,orP?Whatwouldyouneedto
knowinordertodeterminethemolesofthatelementforcomparison?
3) Howdoestheprocessofdeterminingthewatersofhydrationcomparetotheprocessofdeterminingtheempiricalformula?
RhymeTime:Remember,
%tomass→masstomole→dividebythesmallest→makeitwhole
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DeconstructionExercise,anoldiebutgoodie,1990Anexperimentisperformedtodeterminetheempiricalformulaofacopperiodideformedbydirectcombinationofelements.Acleanstripofcoppermetalisweighedaccurately.Itissuspendedinatesttubecontainingiodinevaporgeneratedbyheatingsolidiodine.Awhitecompoundformsonthestripofcopper,coatingituniformly.Thestripwiththeadheringcompoundisweighed.Finally,thecompoundiswashedcompletelyfromthesurfaceofthemetalandthecleanstripisdriedandreweighed.
Massofcleancopperstrip 1.2789grams
Massofcopperstripandcompound 1.2874grams
Massofcopperstripafterwashing 1.2748grams
Determine:
(a) Thenumberofmolesofiodinethatreacted(b) Thenumberofmolesofcopperthatreacted(c) Theempiricalformulaforthecopperiodide.
First,intheprompt,circlewhatweareaskedtodetermine.Assoonasyousee“empiricalformula”think“I’llneedmoles.”Next,thinkaboutallthewayswecanfindmoles–fromgrams?FromPV=nRT?Frommolarityandvolume?Whatinformationdowehave?
Lookatthethreevaluesgiveninthedatatable–whichdifferenceswouldgiveususefulinformation?(1)and(2)?(2)and(3)?(1)and(3)?Calculateeachandlabelwhattheyrepresent:
Now,tackledeterminingthenumberofmoles,parts(a)and(b).Onceyouhavemolesofeach,determinethemoleratioandtheempiricalformula(c).
StrategyHint:Whenyouseeadatatable
thathasmasseswith/withoutorbefore/afterthere’s
probablyagoodchanceyouaregoingtoneedtosubtractvaluestogetsomethinguseful.
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IndependentPracticeHydrateLab2008Q2,parts(a),(b)and(c)Inthefirstoftwoexperiments,astudentisassignedthetaskofdeterminingthenumberofmolesofwaterinonemoleofMgCl2・nH2O.Thestudentcollectsthedatashowninthefollowingtable.
Massofemptycontainer 22.347gInitialmassofsampleandcontainer 25.825g
Massofsampleandcontainerafterfirstheating 23.982gMassofsampleandcontaineraftersecondheating 23.976gMassofsampleandcontainerafterthirdheating 23.977g
(a) Explainwhythestudentcancorrectlyconcludethatthehydratewasheatedasufficientnumberoftimesinthe
experiment.(b)Usethedataaboveto
(i)calculatethetotalnumberofmolesofwaterlostwhenthesamplewasheated,and(ii)determinetheformulaofthehydratedcompound.
(c) Adifferentstudentheatsthehydrateinanuncoveredcrucible,andsomeofthesolidspattersoutofthecrucible.Thisspatteringwillhavewhateffectonthecalculatedmassofthewaterlostbythehydrate?Justifyyouranswer.
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NATIONALMATH + SCIENCEINITIATIVE
ReactionStoichiometryMentalMathMoleRatiosThemole:moleratioisattheheartofreactionstoichiometryproblems.ManyofyouuseDimensionalAnalysistosolvestoichiometryproblems,butforthesakeofsolidifyingyourconceptualunderstanding,completethefollowingexerciseusingonlymentalmath–nocalculatorsorscratchworkallowed.Plus,it’sgoodpracticeforthemultiplechoicesection!
Canyouextendthisideatolimitingreactantproblems?
2HCl Mg → MgCl2 H2
Available 0.10mol 0.10mol →
used → made
Available 0.02mol 0.10mol →
used → made
C3H8 5O2 → 3CO2 4H2O
0.10mol →
0.5mol →
1.0mol →
2.0mol →
4Al 3O2 → 2Al2O3
0.10mol →
0.5mol →
→ 1.0mol
2.0mol →
2KMnO4 5H2SO3 → 2MnSO4 K2SO4 2H2SO4
0.10mol →
0.5mol →
→ 1.0mol
→ 1.0mol
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NATIONALMATH + SCIENCEINITIATIVE
Stoichiometryquestionsarelikelytopopupanywhereonthetest.Anytimethereisachemicalreactioninvolved,stoichiometryisapossibilty.Thebasicpremiseofallstoichiometryproblemsisthis:Findmolesofsomething→useittofindmolesofsomethingelse→dosomethingwithyournewmolevalueConsidersomeofthewaystogettomolesinaproblem:
TurnandTalkMatcheachofthesepromptstooneoftheapproachesinthefigureabove:
1) Whatmassofhydrochloricacidcan3.0gofsodiumbicarbonateneutralize?2) Whatvolumeof0.10MsilvernitratesolutionwouldbenecessarytoprecipitatealloftheCl-fromamixtureof
0.10Lof0.15Msodiumchlorideand0.25Lof0.20MMgCl2solutions?3) Giventhedecompositionofliquidwaterintogaseousoxygenandhydrogen,whatmassofwaterisnecessaryto
form1.5LofO2at315Kand0.957atm?4) WhatmassofLithium,ingrams,reactscompletelywith50.0mLofnitrogengasatSTP?5) Whatmassofwaterisproducedfromthereactionof3.0x1023moleculesofhydrogenwithexcessoxygen?
StoichiometryGoldenRule:
FindthemolesofSOMETHING,ANYTHING
g/mm
MOLES
MxL
PV/RTL/22.4atSTP
Particles/6.02x1023
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DeconstructionExercise2008Q2parts(d)and(e)
Considerthescenariotheyaredescribing.IsachemicalreactioninvolvedintheprecipitationofAgCl?WritethereactionthatisoccurringtoprecipitatetheAgClfromthemixture.Part(d)asksustodescribeaproceduretodeterminehowmuchAgClisprecipitated.Thinkaboutreactionsyou’veseeninlabthatproducedaprecipitate.YoumixsolutionAwithsolutionBandsomethingcloudyhappens.Thenwhat?Howdoyouretrievethesolid?Whatdatadoyouneedtorecord?Writedownyourstepshere:Part(e)assumesthatthestudentsuccessfullyfollowedaproceduresimilartotheoneyouproposed,andisnowreadytodothetwocalculationsfor(i)molesand(ii)percent.Rememberthegoldenruleofstoichiometry?FINDTHEMOLESOFSOMETHING.Wehave2massvaluesthatwouldbegoodcandidates.(1)themassofthemixture,2.94gand(2)themassofpureAgClcollected,5.48g.TheAgClshouldbetheobviouschoicesincewecandetermineandusethemolarmassofAgCl.Now,calculatethenumberofmolesofAgClinthe5.48grams.
Inthesecondexperiment,astudentisgiven2.94gofamixturecontaininganhydrousMgCl2andKNO3.TodeterminethepercentagebymassofMgCl2inthemixture,thestudentusesexcessAgNO3(aq)toprecipitatethechlorideionasAgCl(s).(d)Startingwiththe2.94gsampleofthemixturedissolvedinwater,brieflydescribethestepsnecessarytoquantitatively
determinethemassoftheAgClprecipitate.(e)ThestudentdeterminesthemassoftheAgClprecipitatetobe5.48g.Onthebasisofthisinformation,calculateeach
ofthefollowing.(i)ThenumberofmolesofMgCl2intheoriginalmixture(ii)ThepercentbymassofMgCl2intheoriginalmixture
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WhatisthemoleratiobetweenAgClandMgCl2fromyourbalancedequation?UseittoconvertmolesofAgCltomolesofMgCl2togettheanswerfor(i).
Part(ii)asksforthepercentbymassofMgCl2intheoriginalmixture.Inthiscase,thePARTis__________________________________andtheWHOLEis______________________________________
Sinceweneedapercentbymass,we’llneedthemassofMgCl2present.Easyenough,wejustcalculatedmolesofMgCl2in(i)soasimpleconversionwithmolarmassshoulddothetrick.(ii)Now,setupthepercentfraction,PARToverWHOLEx100,andsolve.
StrategyHint:Alwaysthinkof
percentagesasPARToverWHOLEx100,thenidentifywhatPARTandWHOLErepresentinthegivencontext.
StrategyHint:SinceweweregivenamassofAgClbutaskedaboutan
amountofMgCl2–stoichiometryisinourfuture.The
mole:moleratiowillbekey.
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IndependentPracticeGravimetricAnalysis2014Q1
MassofKItablet 0.425gMassofthoroughlydriedfilterpaper 1.462gMassoffilterpaper+precipitateafterfirstdrying 1.775gMassoffilterpaper+precipitateafterseconddrying 1.699gMassoffilterpaper+precipitateafterthirddrying 1.698g
AstudentisgiventhetaskofdeterminingtheI−contentoftabletsthatcontainKIandaninert,water-solublesugarasafiller.Atabletisdissolvedin50.0mLofdistilledwater,andanexcessof0.20MPb(NO3)2(aq)isaddedtothesolution.Ayellowprecipitateforms,whichisthenfiltered,washed,anddried.Thedatafromtheexperimentareshowninthetableabove.(a)Forthechemicalreactionthatoccurswhentheprecipitateforms,
(i)writeabalanced,net-ionicequationforthereaction,and(ii)explainwhythereactionisbestrepresentedbyanet-ionicequation.
(b)Explainthepurposeofdryingandweighingthefilterpaperwiththeprecipitatethreetimes.(c)Inthefiltratesolution,is[K+]greaterthan,lessthan,orequalto[NO3
−]?Justifyyouranswer.(d)Calculatethenumberofmolesofprecipitatethatisproducedintheexperiment.(e)CalculatethemasspercentofI−inthetablet.(f)Inanothertrial,thestudentdissolvesatabletin55.0mLofwaterinsteadof50.0mLofwater.Predictwhetherthe
experimentallydeterminedmasspercentofI−willbegreaterthan,lessthan,orequaltotheamountcalculatedinpart(e).Justifyyouranswer.
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MultipleChoicePracticeRememberNOCALCULATOR–mentalmathonly!(1) 2H2O(l)+4MnO4
−(aq)+3ClO2
−(aq)à4MnO2(s)+3ClO4
−(aq)+4OH−
(aq)
Accordingtothebalancedequationabove,howmanymolesofClO2
−(aq)areneededtoreactcompletelywith20.
mLof0.20MKMnO4solution?(A)0.0030mol(B)0.0053mol(C)0.0075mol(D)0.030mol
(2) 2N2H4(g)+N2O4(g)à3N2(g)+4H2O(g)When8.0gofN2H4(32gmol-1)and92gofN2O4(92gmol-1)aremixedtogetherandreactaccordingtotheequationabove,whatisthemaximummassofH2Othatcanbeproduced?(A)9.0g(B)18g(C)36g(D)72g
(3) CS2(l)+3O2(g)→CO2(g)+2SO2(g)WhatvolumeofO2(g)isrequiredtoreactwithexcessCS2(l)toproduce4.0LofCO2(g)?(Assumeallgasesaremeasuredat0°Cand1atm.)(A)12L(B)22.3L(C)1/3x22.4L(D)2x22.4L
(4) Acompoundcontains1.10molofK,0.55molofTe,and1.65molofO.Whatisthesimplestformulaofthiscompound?(A)KTeO(B)KTe2O(C)K2TeO3(D)K2TeO6
(5) 10HI+2KMnO4+3H2SO4à5I2+2MnSO4+K2SO4+8H2OAccordingtothebalancedequationabove,howmanymolesofHIwouldbenecessarytoproduce2.5molofI2,startingwith4.0molofKMnO4and3.0molofH2SO4?(A)20(B)10(C)8.0(D)5.0
(6) Whena1.25-gramsampleoflimestonewasdissolvedinacid,0.44gramofCO2wasgenerated.IftherockcontainednocarbonateotherthanCaCO3,whatwasthepercentofCaCO3bymassinthelimestone?(CaCO3,100gmol-1)(A)35%(B)44%(C)67%(D)80%
(7) A27.0-gramsampleofanunknownhydrocarbonwasburnedinexcessoxygentoform88.0gramsofcarbondioxideand27.0gramsofwater.Whatisapossiblemolecularformulaofthehydrocarbon?(A)CH4(B)C2H2(C)C4H3(D)C4H6
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MorePractice2009BQ3
2H2O2(aq)→2H2O(l)+O2(g)ThemassofanaqueoussolutionofH2O2is6.951g.TheH2O2inthesolutiondecomposescompletelyaccordingtothereactionrepresentedabove.TheO2(g)producediscollectedinaninvertedgraduatedtubeoverwaterat23.4°Candhasavolumeof182.4mLwhenthewaterlevelsinsideandoutsideofthetubearethesame.Theatmosphericpressureinthelabis762.6torr,andtheequilibriumvaporpressureofwaterat23.4°Cis21.6torr.(a)Calculatethepartialpressure,intorr,ofO2(g)inthegas-collectiontube.(b)CalculatethenumberofmolesofO2(g)producedinthereaction.(c)Calculatethemass,ingrams,ofH2O2thatdecomposed.(d)CalculatethepercentofH2O2,bymass,intheoriginal6.951gaqueoussample.(d) WritetheoxidationnumberoftheoxygenatomsinH2O2andtheoxidationnumberoftheoxygenatomsinO2inthe
appropriatecellsinthetablebelow.
Substance OxidationNumberofOxygenAtoms
H2O2
O2
(f)Writethebalancedoxidationhalf-reactionforthereaction.