Che111:Chapter9PracticeProblemsKey
1.Theunitmostoftenusedtodescribethemassofatomsistheatomicmassunit,whose
symbolisuoramu.Anatomicmassunitisdefinedasexactly____1/12_____________themass
ofanatomofcarbon-12.
2.One_____mole_____________ofcarboncontains6.022×1023carbonatoms
3.Whatistheweightedaveragemassingramsof6.022×1023atomsoftheelements(a)
bromineand(b)nickel?
a)80g
b)59g
4.Amultivitamintabletcontains40milligramsofpotassium.Howmanymolesofpotassium
doeseachtabletcontain?
=1.02x10-3moles
5.Foreachofthefollowingionicsubstances(a)Co2O3and(b)Fe2(C2O4)3,calculateitsformula
massandwriteaconversionfactorthatconvertsbetweenmassingramsandmolesofthe
substance.
a)2(Co)+3(O)=2(59)+3(16)=
1.66x102gCo2O3
1moleCo2O3
b)2(Fe)+3[2(C)+4(O)]=2(56)+3[2(12)+4(16)]=
3.76x102gFe2(C2O4)3
1moleFe2(C2O4)3
6.Amultivitamintabletcontains5μgofnickelintheformofnickel(II)sulfate(NiSO4).How
manymicrogramsofNiSO4doeseachtabletcontain?
=13μgNiSO4
7.Asampleofanioniccompoundthatisusedinthesemiconductorindustryisanalyzedand
foundtocontain53.625gofindiumand89.375goftellurium.Whatistheempiricalformula
forthiscompound?
53.625gIn
1molIn
=0.466/0.466=1
115gIn
In1Te1.5!In2Te3
89.375gTe 1molTe =0.698/0.466=1.5
128gTe
8.Hydralazineisadrugusedtotreatheartdisease.Itis59.99%carbon,5.03%hydrogen,and
34.98%nitrogenandhasamolecularmassof160.178.Whatisthemolecularformulafor
hydralazine?
59.99gC
5.03gH
1molC
12gC
1molH
1gH
=4.999/2.5=2
C2H2N
=5.03/2.5=2
EmpiricalMass=2(12)+2(1)+1(14)=40g/mol
34.98gN
1molN
14gN
=2.5/2.5=1
EmpiricalMass/MolecularMass=160/40=4
C2x4H2x4N1x4!C8H8N4
9.Spodumeneisalithiumaluminumsilicatecontainingtheequivalentof6.5%to7.5%lithium
oxide,Li2O.CrudeoreminedinNorthCarolinacontains15%to20%spodumene.What
maximummass,inkilograms,oflithiumcouldbeformedfrom2.538megagramsofspodumene
containingtheequivalentof7.0%Li2O?
=83kgLi2O