stoichiometry part 1 - kirkmanedthe valency of an element is the number of electrons its atoms lose,...
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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.