SSS CHEM Composition and Rxn Stoich STUDENT v2

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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!

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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 §

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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

http://Pdfaid.com

rmccormick

Typewritten Text

AP Chemistry Equations & Constants

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 =

=

Copyright © 2016 National Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us online at www.nms.org 1

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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)


Science


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


Science


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.


Science


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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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


Science


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.

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SSS CHEM Composition and Rxn Stoich STUDENT v2