CW/HWAssignments2.  Ch.3NotesPartA10/113.  Ch.3packet10/11

PLANNER •  LabsmustbeturnedinbyMondaymorning•  Study–Ch.3&5

Essentialknowledgestandards•  [SPQ-1.A.1]Onecannotcountparticlesdirectlywhileperforminglaboratorywork.Thus,

theremustbeaconnectionbetweenthemassesofsubstancesreactingandtheactualnumberofparticlesundergoingchemicalchanges.

•  [SPQ-1.A.2:Avogadro’snumberprovidestheconnectionbetweenthenumberofmolesinapuresampleofasubstanceandthenumberofconstituentparticles(orformulaunits)ofthatsubstance.

•  [SPQ-1.A.3]:Expressingthemassofanindividualatomormoleculeinamuisusefulbecausetheaveragemassinamuofoneparticleorformulaunitofasubstancewillalwaysbenumericallyequaltothemolarmassofthatsubstanceingrams.Thus,thereisaquantitativeconnectionbetweenthemassofasubstanceandthemumberofparticlesthatthesubstancecontains(n=m/M)

•  [SPQ-2.A.3]:Thechemicalformulathatliststhelowestwholenumberratioofatomsoftheelementsinacompoundistheempiricalformula

•  [SPQ-2.B.1]:Whilepuresubstancescontainmoleculesorformulaunitsofasingletype,mixturescontainmoleculesorformulaunitsoftwoormoretypes,whoserelativeproportionscanvary.

•  [TRA-1.B.1]:Allphysicalandchemicalprocessescanberepresentedsymbolicallybybalancedequations.

•  [SPQ-4.A.2]:Coefficientsofbalancedchemicalequationscontaininformationregardingtheproportionalityoftheamountsofsubstancesinvolvedinthereaction.Thesevaluescanbeusedinchemicalcalculationsinvolvingthemoleconcept.

FLT•  Iwillbeableto:– Calculatethequantitiesofasubstanceoritsrelativenumberofparticlesusingdimensionalanalysisandthemoleconcept

– Explainthequantitativerelationshipbetweenthemassspectrumofanelementandthemassesoftheelement’sisotopes

– Explainthequantitativerelationshipbetweentheelementalcompositionbymassandthecompositionofsubstancesinamixture

– Explainthechangesintheamountsofreactantsandproductsbasedonthebalancedchemicalequationforachemicalprocess

•  BycompletingCh.3Notes

Ch.3:Stoichiometry

ChemicalQuantitiesReview

Recall: Units • Whatareourunitsfor…

– Mass?• Grams!

– Volume?• Liters!

– Amount?• Moles!

What is the mole?

We’re not talking about this kind of mole!

The Mole § Mole (mol) = amount = defined as

the # of carbon atoms in exactly 12 g of carbon-12.

Moles (is abbreviated: mol) § 1 mole = 6.022 x

1023 particles or atoms or molecules

§ Avogadro’s Number = 6.022 x 1023

Similar Words for an amount §  Just like a dozen is 12, or a pair is

two, a mole is an amount. §  One dozen eggs = 12 eggs §  One mole of eggs = 6.022 x 1023

eggs

Figure3.4-One-MoleSamplesofSeveralElements

Table3.1-Comparisonof1MoleSamplesofVariousElements

Moles (is abbreviated: mol) § Writing conversions: mol à

particles

6.022x1023particles

6.022x1023molecules1mol

1mol

Ex/ § How many moles of water is 5.87

x 1022 molecules?

SampleQuestion•  Whichofthefollowingisthemostaccuratedescriptionofamole?a.  Massofcarboninameasuredsampleofcarbonb.  Numberofatomsinanygivenmassofanelementc.  Numberofsodiumionsin58.44gofsodiumchlorided.  Atleasttwooftheseareaccuratedescriptionsofa

mole

SampleQuestion•  Whichofthefollowingisclosesttotheaveragemassofoneatomofcopper?a.  63.55gb.  52.00gc.  58.93gd.  65.38ge.  1.055×10–22g

MolarMass

Atomic & Molar Mass § Molar mass = Mass of 1 mole (g/mol) § Allows us to convert from mol ßà g § Ex/ Molar mass of Carbon

1molC

12.01gC

MolarMassforFormulas

Calculating Formula Mass

Calculate the formula mass of magnesium carbonate, MgCO3.

24.3 g + 12 g + 3 x (16.00 g) = 84.3 g

Thus, 84.3 grams is the formula mass for MgCO3.

MolarMass•  Example•  Calciumcarbonate(CaCO3),alsocalledcalcite,istheprincipalmineralfoundinlimestone,marble,chalk,pearls,andtheshellsofmarineanimalssuchasclamsa.  Calculatethemolarmassofcalciumcarbonateb.  Acertainsampleofcalciumcarbonatecontains4.86

moles•  Whatisthemassingramsofthissample?•  WhatisthemassoftheCO32–ionspresent?

MolarMass•  Solution(a)

•  Thus,themassof1moleofCaCO3(1moleofCa2+plus1moleofCO32-)is100.09g

•  Thisisthemolarmass

MolarMass•  Solution(b)•  Massof1moleofCaCO3is100.09g

– Samplecontainsnearly5moles,orcloseto500g– Exactamountisdeterminedasfollows:

•  Tofindthemassofcarbonateions(CO32–)presentinthissample,realizethat4.86molesofCaCO3contains4.86molesofCa2+ionsand4.86molesofCO32–ions

MolarMass•  Solution(b)

MolarMass•  Trythis:•  Calculatethemolarmassofthefollowingsubstances:

MolarMass•  Trythis:•  Whatnumberofnitrogenatomsarepresentin1.00gofeachofthefollowingcompounds?

SampleQuestion•  Whichofthefollowing100.0-gsamplescontainsthegreatestnumberofatoms?a.  Magnesiumb.  Zincc.  Silverd.  Calciume.  Allsamplescontainthesamenumberofatoms

SampleQuestion•  Forwhichofthefollowingcompoundsdoes1.0grepresent2.27×10–2mol?a.  H2Ob.  CO2c.  NH3d.  C2H6

SampleQuestion•  Massof0.82molofadiatomicmoleculeis131.3g

–  Identifythemoleculea.  F2b.  Cl2c.  Br2d.  I2

SampleQuestion•  Whichofthefollowing100.0-gsamplescontainsthegreatestnumberofoxygenatoms?a.  H2Ob.  N2Oc.  C3H6O2d.  CO2e.  Allofthesampleshavethesamenumberofoxygen

atoms

Recall

MassSpectrometer•  Helpstoaccuratelycomparethemassesofatoms

MassSpectrometer•  Helpsdetermineaccuratemassvaluesforindividualatoms

•  Determinestheisotopiccompositionofnaturalelements

AverageAtomicMass•  Knownasatomicweight(asperIUPAC’sdeclaration),whichisdimensionlessbycustom–  IUPAC-InternationalUnionofPureandAppliedChemistry

•  Sinceelementsoccurinnatureasmixturesofisotopes,atomicmassesareusuallyaveragevalues

SampleQuestion•  Ex/TheatomicnumberofIndiumis49anditsatomicmass114.8g– Naturallyoccurringindiumcontainsamixtureofindium-112andindium-115,respectively,inanatomicratioofapproximately:

a.  6:94b.  25:75c.  50:50d.  75:25e.  94:6

SampleQuestion•  Ex/Youhaveasampleofzinc(Zn)andasampleofaluminum(Al)– Eachsamplecontainsthesamenumberofatoms– Whichofthefollowingstatementsconcerningthemassesofthesamplesistrue?a.  Massofthezincsampleismorethantwiceasgreatasthe

massofthealuminumsampleb.  Massofthezincsampleismorethanthemassofthe

aluminumsample,butitisnottwiceasgreatc.  Massofthealuminumsampleismorethantwiceasgreatas

themassofthezincsampled.  Massofthealuminumsampleismorethanthemassofthe

zincsample,butitisnottwiceasgreate.  Massesofthetwosamplesareequal

PercentComposition

PercentComposition•  WaystoDescribeaCompound’sComposition:•  Intermsofthenumbersofthecompound’sconstituentatoms

•  Intermsofmasspercent(weightpercent)

PercentComposition•  Ex/CalculatingMassPercent•  Carvoneisasubstancethatoccursintwoformshavingdifferentarrangementsoftheatomsbutthesamemolecularformula(C10H14O)andmass– Onetypeofcarvonegivescarawayseedstheircharacteristicsmell,andtheothertypeisresponsibleforthesmellofspearmintoil

•  Computethemasspercentofeachelementincarvone

PercentComposition•  Ex/CalculatingMassPercent-Solution•  Wherearewegoing?

– Tofindthemasspercentofeachelementincarvone– Whatdoweknow?

•  MolecularformulaisC10H14O– Whatinformationdoweneedtofindthemasspercent?

•  Massofeachelement(we’lluse1moleofcarvone)•  Molarmassofcarvone

PercentComposition•  Ex/CalculatingMassPercent-Solution•  Howdowegetthere?

– Determinethemassofeachelementin1moleofC10H14O

PercentComposition•  Ex/CalculatingMassPercent-Solution

– WhatisthemolarmassofC10H14O?

– Whatisthemasspercentofeachelement?•  Findthefractionofthetotalmasscontributedbyeachelementandconvertittoapercentage

PercentComposition•  Ex/CalculatingMassPercent-Solution

•  Realitycheck–  Individualmasspercentvaluesshouldtotalto100%withinround-offerrors

•  Inthiscase,percentagesaddupto100%

PercentComposition•  TryThese:•  Calculatethepercentcompositionbymassofthefollowingcompoundsthatareimportantstartingmaterialsforsyntheticpolymers:a.  C3H4O2(acrylicacid,fromwhichacrylicplasticsare

made)b.  C4H6O2(methylacrylate,fromwhichPlexiglasismade)

SampleProblem•  Whichofthefollowing100.0-gsamplescontainsthehighestpercentoxygenbymass?a.  H2Ob.  N2Oc.  C3H6O2d.  CO2e.  Allofthesampleshavethesamepercentoxygenby

mass

Mole–VolumeRelationship

Mole-Volume Relationship § Volume may be affected by

§ (1) Temperature § (2) Pressure

§ Consequently, we need to compare gases at a constant temperature and pressure for consistency

Mole-Volume Relationship § Standard

Temperature and Pressure (STP): § 1 atm of

pressure and 273 K (0°C)

Mole-Volume Relationship § Molar Volume:

§ At STP, 1 mole of any gas occupies a volume of 22.4 L

1mol

22.4L

22.4L

1mol

SampleProblems

Example § What is the volume of 4.59 mole of

CO2 gas at STP?

Recall § Density = mass/volume (g/L)

Example § The density of a gas is 1.964 g/L

at STP. What is the molar mass of the gas?

CHEMICALEQSREVIEW

Chemical Equations • Chemical Equation = Shorthand for a

chemical rxn using formulas and symbols

Chemical Equations

•  There are two parts to a reaction: 1.  Reactants = substances you start

with 2.  Products = substances you end up

with

Symbols • à = “yields” or “reacts to form”

Reactants à Products

Symbols •  + = “and”

Cu + Cl2 à CuCl2

Symbols • States of matter = indicated with

subscripts (s), (l), (g), or (aq)

2H2(g) + O2(g) à 2H2O(l)

Symbols •  aq = aqueous = dissolved in water

NaCl(aq) à Na+ + Cl-

Symbols • Double arrow = reversible rxn

Symbols • Others: Heat (Δ), energy, and

catalysts can be indicated on arrows

Symbols • A catalyst is a substance that is

added to speed up a reaction, but is not used or consumed by the reaction

WritingEquations

Writing Equations • Ex 1/ Bromine and potassium iodide

react to form potassium bromide and iodine

***NOTE*** • Diatomic gases =

H, N, O, F, Cl, Br, I • Write as diatomic if

they are by themselves in a chemical equation

Writing Equations • Ex 2/ Iron and oxygen react to form

iron (III) oxide

Now, read these equations:

Fe(s)+O2(g)→Fe2O3(s)

Cu(s)+AgNO3(aq)→Ag(s)+Cu(NO3)2(aq)

NO2(g)N2(g)+O2(g)→

ConservationofMass

Law of Conservation of Mass •  Law of Conservation of Mass =

mass in a closed system can neither be created nor destroyed

Law of Conservation of Mass • What does this mean for us?

– In a balanced chemical equation, the number and kinds of atoms on each side of the equation should be equal.

Law of Conservation of Mass

Balancing Equations • A balanced equation has the same

number of each element on both sides of the equation

Balancing Equations • We use coefficients to indicate

multiples of molecules or compounds

Balancing Equations • Coefficients are multiples of the

entire formula • How does this affect each atom?

Rules 1.  Write out correct formulas (if not

already written) Ex/ Li + H3PO4 à H2 + Li3PO4

Rules 2. Count the number of atoms of each type on both sides

–  If possible, keep polyatomic ions together

Ex/ Li + H3PO4 à H2 + Li3PO4

Rules 3. Balance the elements one at a time by adding coefficients in front.

à Generally, balance H, O, & monatomic atoms last

Ex/ Li + H3PO4 à H2 + Li3PO4

Rules 4. Double-check – always Ex/ Li + H3PO4 à H2 + Li3PO4

Rules Never’s: •  Never add or change subscripts on

formulas •  Never put a coefficient in the middle of a

formula

Try These: 1.  AgNO3+Cu→Cu(NO3)2+Ag

2.  CH4+O2→CO2+H2O

3.  C3H8 + O2 à H2O + CO2