5th day composition stoichiometry
TRANSCRIPT
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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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Ta#ular solution to E(am%le .
11.746
7.340
moles
/r n ns $/
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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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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,