Chemistry11MoleII

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1. UnitConversions

UnitConversions• Youmustfollowthesamemethodshownbelow.

• Wecanconvertfromoneunittoanotherbyusingrelationshipsthatareequivalenttoeachotherthen

arrangedasaratio.Theratioiscalledtheconversionfactor.

• Forexample,withtimeweknowthefollowingrelationships:

Relationship ConversionFactor

1min=60s

1min60s

and 601mins

1hour=60min

160minhour and 60min

1hour

24hours=1day

124dayhours

and 241hoursday

Notethatthevaluesintheratiosareequaltoeachother(i.e.1min=60s).Therefore,theratioreally

hasavalueequalto1.Multiplyinganyfactorbytheconversionfactorisequivalenttomultiplyingby1andwillnotchangethevalueoftheexpression.

Thegeneralformulaforsolvingproblemsusingtheconversionfactormethod:

UnknownAmount=(initialamountgivenintheproblem)x(conversionfactor) Examples:

1. Howmanysecondsaretherein49.56minutes?

49.56 minutes × 60 seconds1 minute = 2973.6 seconds = 2974 seconds (4 sig figs)

2. Howmanyhoursaretherein448.2minutes?

3. Howmanyminutesaretherein44days?(2steps)

4. Howmanysecondsaretherein3days?(3steps)

5. Howoldareyouinseconds? Note:

• Alltheunitscanceleachotherexceptthedesiredunit(s).• Theexpression“3days”ismultipliedbythreeconversionfactorsthatareallequivalentto

“1”.Thefinalanswerchangedbecausethe“expression”hasadifferentunit,buttheactualvalueisstillthesame.

6. Ifthedensityofseawateris1.2g/mL,calculatethevolumeof45gofseawater.

45g × 1mL1.2g = 37.5 mL = 38 mL (2 sig figs)

7. Ifacarismovingat50.0km/h,calculatehowfar(inmetres)thecarmovesin5.00seconds.

ALWAYSINCLUDETHEUNITSFORALLTHECALCULATIONSWEDOINCHEMISTRY.DONOTBETEMPTEDTOEXCLUDETHEM!

MoreExamples:

8. Howmanyminutesaretherein1.67week?

9. Howmanycentimetersarein21.598km?

10. Ifyouhave45dozeneggs,howmanyeggsdoyouhave?

11. Ifacarcanmove50.0km/h,howfarcanthecargoin3.2675hours?

12. Onemoleculeofphosphorushas4atoms.Howmanymoleculesaretherein448atomsof

phosphorus?

13. Ifonemoleofcarbonhasamassof12.0g,whatisthemassof4.7molesofcarbon?

14. Thedensityofaluminumis2.7g/mL.Whatisthevolumeof7.4gofaluminum?

15. Ifacaraverages60.0km/h,howlongwillittaketocover57km? “Onlythosewhohavethepatiencetodosimplethingsperfectlywillacquiretheskilltodo

difficultthingseasily.” ~JohannvonSchiller(Germanphilosopher)B.MultipleUnitConversions

16. Howmanyminutesaretherein3days?

17. Theenergyneededtomelt1kgoficerequires334kJ.Thelargestknowniceberghasavolumeofabout3.1x1013m3.Howmuchheatwasrequiredtomelttheicebergif1.0m3oficehasamassof917kg?

18. Howfardoesacargoin10.00secondsifitismovingat50.00km/h?

19. If1yard=3feet,1foot=12inches,and1inch=2.54cm,howmanymetersarein50.00yards?

20. Asprintercanrun100.metresin10.0seconds.Howfastisthesprintermovinginkm/h?

21. Achickenfarmerwishedtopurchaseagiftforhiswife.Thegiftwasworth2horses.Atthelocalmarket,3horseswereworth5cows,1cowwasworth4hogs,3hogswereworth4goats,and1goatcost9chickens.Howmuchwasthegiftgoingtocostthefarmerwhohadtopayinchickens?

22. Trythisthischallengingconversion!Suppose1dip=6dops,1dop=8daps,1tick=13tocks,and1tock=10tacks.Convert21.1dips/tack2intodops/tock2.

1)2974sec2)7.470hr3)63,000min4)3x105sec5)9.2x108sec6)38mL7)69.4m8)1.68x104min9)2.1598x106cm10)540eggs11)163km12)112molecules13)56g14)2.7mL15)0.95hr16)4x103min17)9.5x1018J18)0.1389km19)45.72m20)36.0km/h21)160chickens22)1.27x104dops/tocks2