5th Day Composition Stoichiometry

8/9/2019 5th Day Composition Stoichiometry

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omposition Stoichiometry

Louie Paolo D. CarpioInstructor 3

Institute of Chemistry, UP Diliman


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OBJECTIVES for today

1. Review relevant concepts

2. Discuss the Law of Definite Composition

3. Differentiate empirical formula fromactual formula

4. Solve problems in composition

stoichiometry.


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SI!!S you "ill #e learnin$

1. Solvin the chemical formula !both

empirical an" actual formula# base" on the

iven mass percentaes of elements.

2. Solvin the chemical formula fromcombustion analysis.

3. Solvin the chemical formula from a iven

reaction.


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!a" of Definite Com%osition

Law of Definite Composition& $lements may react with other elements in

specific ratios to form a compoun". %hese

specific ratios can be "escribe" by&

!1# fi'e" mass percentaes of each element

in the compoun"

!2# fi'e" particle ratio in the compoun"

& (or a iven compoun") these proportions

are in"epen"ent of time) location)

temperature) pressure) etc.


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!a" of Definite Com%osition

*llustration of Law of Definite Composition

$'ample& C+2has a "efinite composition of

2.one atom of carbon an" 2 atoms of o'yen

3.12.,11 !2-.3 # of carbon an" 32.,,,

!-2.-# of o'yen for each 44.,11 of C+2

& %his "efinite composition is in"epen"ent oflocation) time an" other con"itions

& %his law is only use" to "escribe

compoun"s an" not chemical reactions


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'ass Percenta$es

/ass percentae of an element in a

compoun" can be calculate" from

the e0uation&

( )

=

compoun"theofmassmolar

compoun"ofmoleainelementofmass1,,$


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E(am%le )

Solve for the mass percentaes ofcarbon an" o'yen in the compoun"

C+2.

// C+2 1 !C# 2 !+#

// C+2 12.,11 mol 2!1.,, mol#

// C+2 44.,11 mol

1. Solve for the molar mass of C+2


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E(am%le )

Solve for the mass percentaes ofcarbon an" o'yen in the compoun"

C+2.

2. Solve for the mass of each atom

( )

2-.25C

3mol44.,113mol12.,111,,C

=

= ( )

-2.-1+

mol44.,11mol#!1.,,21,,+

=

=

// C+2 44.,11 mol


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Chemical *ormula

%he "efinite composition of a substance canbe easily "escribe" by its chemical formula.

%here are 2 types of chemical formula&

3. empirical formula 6 7simplest8 formula

where the simplest or smallest whole

numbers are use"

4. actual formula 6 the actual number of atomsin the molecule or formula unit is written


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Chemical *ormula

$'ample&

%he compoun" 7"e'trose8 has an actual

chemical formula of C912+. :hat is its

empirical formula;


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Chemical *ormula

%here are 3 types of molar masses base" onthe chemical formula&

3. empirical mass 6 molar mass base" on the

empirical formula

4. molecular mass 6 molar mass base" on the

actual formula of a molecular compoun"

>. formula mass 6 molar mass base" on the

actual formula of an ionic compoun"


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Chemical *ormula

$'ample&%he compoun" 7"e'trose8 has an actual

chemical formula of C912+. :hat is its

empirical formula. Determine its empiricalan" molecular mass.


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$'ample&

%he compoun" "iborane has an empirical

formula of A93 an" has a molar mass of

2-.- mol. :hat is its actual formula;1. Solve for the empirical mass !$/#&

$/ !1# !A# 3 !9#

$/ 1,.?1 mol 3 !1.,,? mol#

$/ 13.?24 mol

E(am%le


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$'ample&

%he compoun" "iborane has an empirical

formula of A93 an" has a molar mass of

2-.- mol. :hat is its actual formula;3. Solve for the actual formula&

E(am%le


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Chemical *ormula

$mpirical formula& C92+

< chemical formula "escribes moleratio of elements in substance.

1 mole C & 2 moles 9 & 1 mole +


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Definition of Composition Stoichiometry

Composition Stoichiometry

6 "escription of 0uantitative

relationshipsamon elements incompoun"s

B these 0uantitative relationships are

usually "escribe" in terms of massratios or mole ratios of elements in a

substance


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Determination of Chemical (ormula

Determination of the chemical

formula is focuse" on establishinthe simplest mole ratios.


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Schematic Dia$ram of Sol-in$

Com%osition Stoichiometry Pro#lems

1. Determine the mass ratio !or mass percentaes#of elements in the substance

2. Solve for the mole ratios by assumin 1,, of

substance3. $stablish the simplest whole number ratio tosolve for the empirical formula

4. =et the empirical mass of the substance base"on the empirical formula

>. =et the ratio of molar mass an" empirical massto et actual formula

/r

n

nsr

$/


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$'ample&


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Ta#ular solution to E(am%le 3

21.59 gO

13.60 gH

64.81 gC

Mass

ratioatom

1.349

13.492

5.396

moles

C+$R% %+ /+L$S

E molar mass ofatom

E 12.,11 mol

E 1.,,? mol

E 1.,,, mol

/r n ns $/


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Ta#ular solution to E(am%le 3

/r n ns $/


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Solution to E(am%le 3

/r n ns $/


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$'ample& < compoun" is ??.1 C an"

11.?4 9 by mass. *ts molar mass is

2,4.4 mol. :hat is the empirical an"molecular formula of the compoun";

1. Determine mass ratios2.


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Ta#ular solution to E(am%le .

11.84 gH

88.16 gC

Mass

ratioatom

11.746

7.340

moles

C+$R% %+ /+L$S

E molar mass ofatom

E 12.,11 mol

E 1.,,? mol

/r n ns $/


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11.746

7.340

moles

/r n ns $/


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/r n ns $/


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/r n ns $/


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Solution to E(am%le 3

/r n ns $/ 9?

$/ ?.115 mol // 2,4.4 mol

3mol?.115

mol2,4.4

massempirical

massmolar@ ==


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$'ample& >.?> mol + 1.,, mol


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& Fsually "one for compoun"s

containin C) 9 an" +.

& Compoun"s are 7burne"8 with +2 an"the pro"ucts are C+2 an" 92+ for

complete combustion

& (or incomplete combustion) C+ ispro"uce" instea" of C+2

Combustion analysis problems


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C+/AFS%*+ R$


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< ,.2,,, ram sample of pure

hy"rocarbon !contains C H 9 only#

was burne" to pro"uce ,.>?>> ram of

C+2an" ,.3>5> ram of 92+. Determine

!1# the empirical formula of the

compoun" !2# the mass percentaes of

C an" 9 in this hy"rocarbon.

$'ample >


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$'ample >

+92yC+'+

4y'9C 222y' +

++

,.2,,, ,.>?>> ,.3>5>

*mportant mole ratios base" on thereaction

2. 1 mole C+2& 1 mole C

3. 1 mole 92+ & 2 moles 9


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$'ample >

+92

yC+'+4

y'9C 222y' + ++

,.2,,, ,.>?>> ,.3>5>

3H atom

0.039910.019950.3595 gH2O

1C atom

0.01330

0.013300.5855 gCO2

Simplest

mole ratio

of atoms

Moles ofatom

Moles ofompo!"#

Massmole!le


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< ,.2,,, ram sample of pure hy"rocarbon!contains C H 9 only# was burne" to pro"uce ,.>?>>

ram of C+2 an" ,.3>5> ram of 92+. Determine !1#

the empirical formula of the compoun" !2# the mass

percentaes of C an" 9 in this hy"rocarbon.

$'ample >

$mpiricalformula& C93

3H atom

0.03991

1C atom0.01330

Simplest mole

ratio of atoms

Moles of

atom


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Solve for mass percentaes

$'ample >

$mpirical mass of C93&

1!C# 3!9# 12.,11 mol 3 !1.,,? mol#

$/ 1>.,3> mol

( )

-5.?5C

mol1>.,3>

mol12.,111,,C

=

=

( )

2,.119

mol1>.,3>mol#!1.,,?31,,9

=

=


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2.,, rams of a compoun" containin

C) 9 an" + was reacte" with e'cess +2to form 3.> of C+

2

an" 1.4 of 92

+.

Solve for the empirical formula of the

compoun".

$'ample

+92

yC+'+

2

G

4

y'+9C 222Gy' + ++


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$'ample

+92yC+'+

2G

4y'+9C 222Gy' +

++

2.,, 3.> 1.4

PR+AL$/& there are two sources ofo'yen atoms

2. o'yen atoms in the unInown compoun"3. o'yen atoms from +2

!3.,2 #


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$'ample

+92yC+'+

2G

4y'+9C 222Gy' +

++

2.,, 3.> 1.4

Solution&

2. Solve for moles of C an" 9 first

3. Solve for rams of + in the actualcompoun"

4. Convert rams in J 2 into moles of +

>. Solve for empirical formula

!3.,2 #


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$'ample

H atom

0.1634 g

H atom

0.16210.081041.46 gH2O

C atom

0.9716 g

C atom

0.08089

0.080893.56 gCO2

$rams ofatom

Moles ofatom

Moles ofompo!"#

Massmole!le

+92

y

C+'+2

G

4

y

'+9C 222Gy' +

++

2.,, 3.> 1.4 !3.,2 #


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$'ample

+92

y

C+'+2

G

4

y

'+9C 222Gy' +

++2.,, 3.> 1.4

%he 2.,, rams of the compoun" shoul"come from the mass of C) 9 an" + in thecompoun". %herefore&

!3.,2 #

2.,, rams rams C rams 9 rams +

2.,, rams ,.5-1 ,.134 !rams +#

!rams +# 2.,, rams 6 !,.5-1 ,.134 #

!rams +# ,.?>1 rams


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$'ample & e'ten"in the table

H atom

3

H atom

0.16210.081041.46 gH2O

O atom

1

O atom

0.054070.054070.8651 gO

C atom

1.5

C atom

0.080890.080893.56 gCO2

Simplest

mole ratio

Moles of

atom

Moles of

ompo!"#Massmole!le

+92

y

C+'+2

G

4

y

'+9C 222Gy' +

++2.,, 3.> 1.4 !3.,2 #

T # l l ti t E l /


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Ta#ular solution to E(am%le /

/r n ns $/


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Ta#ular solution to E(am%le /

/r n ns $/


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$'ample.2.3,3 rams of @enon as reacts with

1.334 rams of fluorine as to form an

unInown compoun" compose" of@enon an" fluorine only. :hat is the

formula of the compoun";

averae atomic masses&

@e 131.2, mol ( 1?.55? mol

Reaction analysis problems


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$'ample.2.3,3 rams of @enon as reacts with

1.334 rams of fluorine as to form an

unInown compoun" compose" of@enon an" fluorine only. :hat is the

formula of the compoun";

Reaction analysis problems


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e't meetin

& Solution stoichiometry& titrations& Reaction stoichiometry 2& limitin

reaents in a chemical reaction


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$n" of Class

& Kuestions;;;& Chapters covere" to"ay

Chapters 2B4 to 2B1,

Documents

5th Day Composition Stoichiometry