Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large...

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Ch 6. Chemical Composition Chem 30A

Transcript of Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large...

Page 1: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Ch 6. Chemical Composition

Chem 30A

Page 2: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

The Mole

Page 3: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

The Mole •  Inlaboratories,largenumbersofatomsareusedforexperiments,soscien6stsmadeupaunittoavoidusingverylargenumbers:mole(mol)

•  Themoleisaunitofmeasure:1dozen=121gross=1441mole=6.02214x1023

Avogadro’snumber(NA)

1dozeneggs=12eggs1moleeggs=6.02214x1023eggsàhugenumber!

Page 4: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

The Mole

Themoleisusefulforcoun6ngatoms,molecules,andions.

•  1molof12Catoms=6.022x102312Catoms•  1molofH2Omolecules=6.022x1023H2Omolecules•  1molofNO3

-ions=6.022x1023NO3-ions

Page 5: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Converting Between Moles and # of Particles

6.022x1023par6cles/mol

moles numberofpar6cles

ExProbs

(Canbeatoms,ions,ormolecules)

Page 6: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Where Did Avogadro’s Number Come From?

•  Itwasmeasured!

•  Thevalueofthemole(Avogadro’snumber,NA)isbasedon12Cstandard:

NA=thenumberofatomsinexactly12gof12C =6.02214x1023

Sobydefini6on:1molof12Catomshasamassof12g.

Page 7: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Relationship Between amu/atom and g/mole

•  Bydefn:1atomof12Chasamassof12amu.•  Bydefn:1moleof12Chasamassof12g.

•  So,massof12C=

atomicmass molarmass•  Molarmass:themassofonemoleofasubstance

[g/mol]

12 amu and 12 g atom mol

Page 8: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Relationship Between Atomic Mass and Molar Mass

1 amu = 1 g atom mol

#atomicmass[amu] = #molarmass[g]

Becausetheatomicmassesofallotherelementsarerela6vetoatomicmassof12C,thisrela6onshipbetweenatomicmassandmolarmassistrueforeveryelement.

Page 9: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Atomic Mass [amu] = Molar Mass [g]

Substance AtomicMass MolarMassC 12.01amu/atom 12.01g/molMg 24.30amu/atom 24.30g/molO 16.00amu/atom 16.00g/molAg 107.87amu/atom 107.87g/molHe 4.00amu/atom 4.00g/mol

Nowweknowthemolarmassofanatombylookingattheperiodictable!

Similarly,formolecules:formulamass[amu]=molarmass[g]

ExProbs

Page 10: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Converting Between Moles and Mass

Wecanusethemolarmass(g/mol)toconvertbetweenthemolesofpar6clesandthemass(ing)ofasubstance:

molarmass(g/mol)

gramsofsample

molesofsample

ExProbs

Page 11: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Grams-Moles-Number of Particles Conversions

ExProbs

molarmass[g/mol]

6.02x1023par6cles/mol

grams moles No.ofpar6cles

Page 12: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Amounts of an Element in a Compound

ChemicalFormulasasConversionFactors•  Findmoleselementingivenmolesofcompound.

– Howmanymolesofcarbonarein0.245moleofC6H12O6?

•  Findgramsofelementingivengramsofcompound.– Howmanygramsofcarbonarein1.50gofC6H12O6?

ExProbs

*Mustgothroughmolerela6onship:molofelement molofcompound

Page 13: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Mass Percent Composition of Compounds

Page 14: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Mass Percent Composition

•  Massfrac6onofanelementinacompound= massofanelement massofcompound inasampleofcompound•  Masspercent=massfrac6onx100

Exprobs

•  Masspercentofanelementinacompound= massofanelementincompoundsamplex100massofacompoundincompoundsample

Page 15: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Mass Percent from Chemical Formula

•  Massfrac6onofanelementinacompound=

massofanelementmassofcompoundin1moleofcompound•  Masspercent=massfrac6onx100

Exprobs

•  Masspercentofanelementinacompound= massofanelementin1molofcompoundx100massof1molofcompound

Page 16: Ch 6. Chemical Composition - Laney College · 8/30/2017  · The Mole • In laboratories, large numbers of atoms are used for experiments, so scien6sts made up a unit to avoid using

Mass Percent of an Element in a Compound

ChemicalFormula

MassofelementandMassofcompoundinaGivensample

Mass%ofelementInCompound


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