StoichiometryPart1

FormulaeofsimplecompoundsFormulaeofsimplecompoundscanbededucedfromtheirions/valenciesbuttherearesomethatyoushouldknowoffbyheart.YouwilllearntheseandmoreasthecourseprogressesYoumustlearnthefollowingformulae:CarbondioxideWaterHydrogenSodiumchlorideSodiumhydroxideNitricacidSulfuricacidHydrochloricacidDeducetheformulaefromthemodels:

Howdoyouknowinwhatordertonametheelementsincompounds?

NamingCompoundsWhenthecompoundcontainsametalandanonmetal;thenameofthemetalisgivenfirstthenthenonmetalbutendingin–ide.E.g.Sodiumchloride,Magnesiumoxide,ironsulfide.Whenthecompoundismadeupoftwonon-metals;Ifoneishydrogen,thatisnamedfirst,Otherwisetheonewiththelowergroupnumbercomesfirstthenthenameoftheothernon-metalwithideontheend.e.g.Hydrogenchloride,carbondioxideValencyThevalencyofanelementisthenumberofelectronsitsatomslose,gainorshare,toformacompound.

Group Lose/Gain/shareelectrons

Valency Examples

I

II

III

IV

V

VI

VII

0

Hydrogen

Transitione’s

UsingValenciestowriteformulaeA WritetheformulaofaluminiumoxideModelanswer: Symbol Al O Valency 3 2 “swap”thenumbersandifpossible,cancel/simplify. Al2O3B WritetheformulaforaluminiumphosphideModelanswer: Symbol Al P Valency 3 3 “swap”thenumbersandifpossible,cancel. Al3P3,cancelnumbers:Al1P1,writtenasAlP. Writetheformulaofthefollowingsimplecompounds.

1 lithiumoxide

2 sodiumoxide

3 boronfluoride

4 calciumnitride

5 germaniumchloride

6 arsenicoxide

7 aluminiumsulphide

8 siliconcarbideCCpage67Q’s1–6.

BalancingchargestowriteformulaeYouareexpectedtoknowtheformulaeofalltheionslistedbelow,therewillbeatestatsomepoint.Youhavebeenwarned!

Thenextfewpagesareworksheetsthatwilltestyourskillsondeducingformulaeandbalancingchemicalequations.Pleasedothemyourself!

ChemicalCalculationsRelativeatomicmassdefinition–Ar(sometimeswrittenRAM)RelativeatomicmassandisotopesChlorinehasarelativeatomicmassof35.5!Howcananelementcontainhalfofa

neutron?Theanswerisduetotheisotopesofchlorineandtheirrelativeabundance.

Thereare3timesasmany35Clatomsasthereare37Cl.Sobydoingasimplecalculation

theaveragerelativeatomicmassisadecimal.ThefollowingmethodisusedtodeterminetheAr.

FindingthemassesofmoleculesandionsUsingArvalues,itiseasytoworkoutthemassofanymoleculeorgroupofions.RelativeMolecularMass(RMM)=MrThecombinedmassofalltheatomspresentinthesubstanceRelativeFormulaMass(RFM)=MrThecombinedmassofalltheionspresentinthesubstanceIonshavethesamemassasatomsasthemassofanelectronisnegligibleHydrogen(RMM)Mr:Water(RMM)Mr:SodiumChloride(RFM)Mr:WorkouttheMrofthefollowingsubstances:1 NH3

2 CH4

3 C6H12O6

4 CuSO4CCpages70–71Q’s1,2,3,4.

CalculationsinvolvingreactingmassesIfyouknowtheactualamountoftwosubstancesthatreactyoucan:

PredictotheramountsthatwillreactSayhowmuchproductwillform.

Twolawsofchemistryyoumustremember:

1 Elementsalwaysreactinthesameratiotoformagivencompound.6gofcarboncombineswith16gofoxygentoformcarbondioxide,so……12gofcarboncombineswith32gofoxygen,andsoon…….2 Thetotalmassdoesnotchangeduringachemicalreaction.

Totalmassofreactants=Totalmassofproducts6gofcarboncombineswith16gofoxygentoform22gcarbondioxide,12gofcarboncombineswith32gofoxygentoform44gofcarbondioxide

CalculatingQuantitiesExample1:Astudentobtains48gofmagnesiumsulfatefrom9.6gofmagnesium.What

massofmagnesiumsulfatecanthestudentgetfrom1.2gofmagnesium?

9.6gofmagnesiumgives48gofmagnesiumsulfate(writedowntheinfo!!!)so. 1.2gofmagnesiumgives1.2x48=6gmagnesiumsulfate 9.6Example2:InthereactionMg+CuSO4èMgSO4+Cu.6.4gofcopperareformedfrom

2.4gofmagnesium.Whatmassofmagnesiumisneededtoget32gofcopper? 6.4gofcopperisformedfrom2.4gofmagnesium(writedowntheinfo!!!)so. 32gofcopperrequires32x2.4=12gofmagnesium 6.4CCpages74–75.Q’s1to13.

StoichiometryPart2

TheMoleAnatomisimpossibletoweighonabalance.1000atomsareimpossibletoweighonabalance,amillion,abillionetc.Sowescaleituptoaspecificnumberofatoms,ionsormolecules.Anatomormoleculecanbecalledaunit,theycountas1!Thisnumberis6.02x1023.WecallthisnumberAvogadro’sconstant.Inonemoleofheliumatomsthereare6.02x1023heliumatomsInonemoleofwaterthereare6.02x1023watermoleculesAndsoon..butbecareful..Inonemoleofwaterthereare6.02x1023watermoleculesbutthereareX3atoms!Thatmeansthereare18.06x1024atomsinamoleofwater.Drawbelow:MolarMass-Themassof1moleYoucanfindthemassofonemoleofanysubstancebythesesteps:

1 Writedownthesymbolorformulaofthesubstance2 FinditsArorMr3 Expressthatmassingrams(g).

Forthisyouwillneedtoremembertheformulaofcommoncompoundsandwhichelementsexistnaturallyasmolecules.OxygenexistsasO2forexample.

Completethetable:

Substance Symbolorformula Ar Mr Massof1mole

Helium He He=4 Existsassingleatoms

4g

Oxygen O2 O=16 2x16=32 32gEthanol C2H5OH C=12

H=1O=16

2x12=245 6x1=66 1x16=16

46gWater

H20

CarbonDioxide

Coppersulphate

Sodiumchloride

Youwillneedtolearnthisequationand/orthecalculationtriangle

Numberofmoles(inagivenmass)=mass. massof1moleorMassofagivennumberofmoles=massof1molexnumberofmolesAnswerQ’s1to8inCCpage77.Usetheexamplesabovethequestionsinthetextbooktohelpyou.Completetheworksheetoverthepage.

MolesWorksheet1) Define“mole”.2) Howmanymolesarepresentin34gramsofCu(OH)2?3) Howmanymolesarepresentin2.45x1023moleculesofCH4?4) Howmanygramsaretherein3.4x1024moleculesofNH3?5) Howmuchdoes4.2molesofCa(NO3)2weigh?6) WhatisthemolarmassofMgO?7) Howaretheterms“molarmass”and“atomicmass”differentfromone

another?

CalculationsinvolvingequationsMostquestionsyouwillbeaskedtoanswerwillhaveanequation.Itisveryimportantyouunderstandhowtousemolesandratios.Considerthefollowingreaction:Mg+2HClèMgCl2+H2 IMPORTANT!!!-Thosebignumbersinfrontontheformulaetellusinwhatproportions(inmoles)thesubstancesreact.Thatiswhywebalanceequations.So..1moleofmagnesiumreactswith2molesofhydrochloricacidtogive1moleofmagnesiumchlorideand1moleofhydrogen.Question:Howmanymolesofmagnesiumchlorideareproducedwhen5molesofmagnesiumreactswithanexcessofhydrochloricacid?Mg+2HClèMgCl2+H2

Answer:LookattheratioofMgtoMgCl21moleofMg,gives1moleofMgCl2So5molesofMgmustgiveus5molesofMgCl2

Question:Ifwereact36gofMgwithanexcessofhydrochloricacid,whatmassofMgCl2isproduced?RememberthebignumberareforproportionsinmolesNOTMASS!YoumustworkoutthenumberofmolesfirstBEFOREyouusetheratio.(copythemodelanswerfromboard)Mg+2HClèMgCl2+H2

200gofcalciumcarbonatereactswithanexcessofhydrochloricacid.

1 Writethebalancedequation2 Calculatehowmanymolesofcalciumcarbonatethereare3 Deducehowmanymolesofcarbondioxideareproduced4 Calculatethemassofthecarbondioxideproduced.

123gofglucosereactswithanexcessofoxygen.

1 Writethebalancedequationforglucosereactingwithoxygen.(Respiration)2 Calculatethemassofwaterproduced.

Answerquestions1and2only.P79CC.

MolargasVolume1 mole of any gas occupies 24dm3 at rtp. Thatmeansthat1moleofoxygen,carbondioxide,hydrogenormethanewill24dm3ofspaceatrtp.(rtp=roomtemperatureandpressure)Rememberthatthemassof1molefordifferentgasesisnotthesame!Thevolumeisthesamebutthemassisdifferent.

Theequationyouneedtolearnis:

ExampleSimpleCalculation:Whatvolumedoes0.25molesofagasoccupyatrtp?1moleoccupies24dm3so0.25molesoccupies0.25X24dm3=6dm3

1dm3=1litre.

In1dm3thereare1000cm3

Reacting Masses / Gas Calculations Thestepsinvolvedinacalculationareasfollows: (a)Converttheinformationgiventomolesofonesubstance. (b)Usethechemicalequationtofindmolesofothersubstanceneeded. (c)Convertbackfrommolestomass(orconcentration,volumeetc.)

1. When calcium carbonate is heated, carbon dioxide is evolved: CaCO3 à CaO + CO2

What volume of carbon dioxide (at RTP) is produced from 500g calcium carbonate? [3]

2. 500g calcium carbonate was treated with hydrochloric acid at RTP:

CaCO3 + 2HCl à CaCl2 + H2O + CO2 What volume of CO2 gas was produced? [3]

3. Ammonia is produced in the Haber process according to the equation; N2 + 3H2 à 2NH3

What volume of (i) nitrogen and (ii) hydrogen is required to produce 68g of ammonia, at RTP? [6]

4. When carbon and carbon dioxide are heated together carbon monoxide is produced:

C + CO2 à 2CO. What volume of CO can be produced from 3g carbon at RTP? [4]

5. What volume of oxygen is released when 1000g of sugar, C6H12O6, is photosynthesis at RTP? 6CO2 + 6H2O à C6H12O6 + 6O2 [4] 6. Calculate the volume of i) CO2 and ii) H2O produced when 150 cm3 of methane is combusted. CH4(g) + O2(g) à CO2(g) + 2H2O(g) [4] Q’s1–7p81CC.

ConcentrationTheconcentrationofasolutionisdefinedas:Theunitsare orTheformulayoumustlearnis:pleaselabeltheunitsyoucanuseuseonthebottomrow.

Q’s1–5p83CC.PracticeCalculations:Part1

1) Calculate the number of moles of potassium hydroxide that must bedissolvedtomakethefollowingsolutions:(i) 500cm3of1mol/l

(ii) 200cm3of0.5mol/l

(iii) 100cm3of0.1mol/l

(iv) 2litresof0.25mol/l

(v) 250cm3of2mol/l

2) Calculate the concentration of each of the following solutions ofhydrochloricacid:(i) 1molofHCldissolvedtomake100cm3ofsolution

(ii) 2molofHCldissolvedtomake1litreofsolution

(iii) 0.1molofHCldissolvedtomake500cm3ofsolution

(iv) 0.5molofHCldissolvedtomake250cm3ofsolution

Part21) Calculate thenumberofgramsof substanceneeded tomakeeachof

thefollowingsolutions(i) 50cm3ofNaOH(aq),concentration2mol/l

(ii) 100cm3ofKOH(aq),concentration0.5mol/l

(iii) 1litreofNa2CO3(aq),concentration0.1mol/l

2 Calculatetheconcentrationofeachofthefollowingsolutions:(i) 5.65gofNaCldissolvedtomake1litreofsolution

(ii) 2.5gofCaCO3dissolvedtomake100cm3ofsolution

(iii) 8gofNaOHdissolvedtomake250cm3ofsolution

Toadd:notesonempiricalandmolecularformula,%yield.Pages90–91CC.Allquestions.