chapter 4: chemical quantities and aqueous reactions
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ChemistryTRANSCRIPT
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CHAPTER 4CHEMICAL
QUANTITIES
ANDAQUEOUS
REACTIONS
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Global Warming Scientists have measured an average
0.6 C rise in atmospheric
temperature since 1860
During the same period atmosphericC!levels have risen !"#
$re the t%o trends causal&
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3
'he Sources o( )ncreased C! ne source o( C!is the combustion reactions o( (ossil
(uels %e use to get energ*$nother source o( C! is volcanic action
+o% can %e ,udge %hether the increase in C!is naturalor due to our use o( (ossil (uels&
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4
uantities in Chemical 2eactions
'he amount o( ever* substance used and made in achemical reaction is related to the amounts o( all theother substances in the reaction 3a% o( Conservation o( ass
4alancing e5uations b* balancing atoms
'he stud* o( the numerical relationship bet%eenchemical 5uantities in a chemical reaction is calledstoichiometry.
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Stoichiometric Calculations
'he coe((icients in the balanced e5uation give
the ratio o( moleso( reactants and products.
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Stoichiometr*
stoichiometry:a numerical relationship bet%een
chemical 5uantities in a balanced chemical e5uation allo%s one to predict the amounts o( products that (orm in a
chemical reaction based on the amounts o( reactants
: +!;g!;g+:;g!consumed in the
reaction there are : molecules o( +!and !
molecules o( >+:.
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@5uivalence (or Chemical 2eactions
Since chemists donAt usuall* thinB o( things in terms o(molecules/ *ou can trans(orm these relationships into mole tomole values.
: +!;g!;g+:;g+:.
?or ever* 1 mole o( >!*ou can produce ! moles o( >+:.
?or ever* : moles o( +!*ou %ill need 1 mole o( >!to per(ormthis reaction.
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ole ole 2elationships putting stoichiometric relationships to %orBE
: +!;g!;g+:;g!and more than enough +!/ ho%much >+:can %e maBe&
1 >! F ! >+: conversion (actor ! moles >+:
1 mole >!
moles >!moles >+:
: moles >! ! moles >+: H 6 moles >+:
1 mole >!
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ractice roblems ;moles to moles+:&
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ractice roblems ;grams to
gramsa>:;a5aCl
Solution
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What is the molarit* o( a solution that has !"." g
T4r dissolved in 1.I" 3 o( solution&
'ro- Chemistr*- $ olecular $pproach/ !e
What )s the molarit* o( a solution containing :.J g o(
>+: in !00.0 m3 o( solution&
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sing olarit* in Calculations
olarit* sho%s the relationship bet%een the moles o(solute and liters o( solution
)( a sugar solution concentration is !.0 / then 1 liter o(
solution contains !.0 moles o( sugar
! liters H J.0 moles sugar 0." liters H 1.0 mole sugar
1 3 solution - ! moles sugar
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or
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What volume o( 0.1!" >a+ ;in 3iters< contains
a total o( 0.!"" mol o( >a+&
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Determine the mass o( CaCl! in 1.I" 3 o( 1."0
CaCl!solution.
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What mass o( copper;))< sul(ate pentah*drate %ould
be re5uired to prepare !"0.0 m3 o( a 1.00 solution
o( CuSJ" +!&
'ro- Chemistr*- $ olecular $pproach/ !e
+o% %ould *ou prepare !"0.0 m3 o( 0.1"0
CaCl!&
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Dilution (ten/ solutions are stored as concentrated stoc*
so"$tio%s
'o maBe solutions o( lo%er concentrations (rom these stocBsolutions/ more solvent is added
the amount o( solute doesnAt change/ ,ust the volume o( solutionmoles solute in solution 1 H moles solute in solution !
'he concentrations and volumes o( the stocB and ne%solutions are
inversel* proportional
M1+,1- M+,
3#
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'o %hat volume should *ou dilute 0.!00 3 o( 1".0 >a+
to maBe a :.00 >a+ solution&
'ro- Chemistr*- $ olecular $pproach/ !e
What is the concentration o( a solution prepared b*
diluting J".0 m3 o( 8.!" +>:to 1:".0 m3&
+o% %ould *ou prepare !00.0 m3 o( 0.!" >aCl solution
(rom a !.0 solution&
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Solution Stoichiometr*
4ecause molarit* relates the moles o( solute to the liters
o( solution/ it can be used to convert bet%een amount o(
reactants andor products in a chemical reaction
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3(
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What volume o( 0.1"0 TCl is re5uired to completel*
react %ith 0.1"0 3 o( 0.1I" b;>:
! TCl;aq::;aqonelectrol*tes
aterials that dissolve in
%ater to (orm a solution that
%ill conduct electricit* are
called e"ectro"ytes
aterials that dissolve in
%ater to (orm a solution that
%ill not conduct electricit* are
called %o%e"ectro"ytes
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olecular Lie% o(
@lectrol*tes and >onelectrol*tes
'o conduct electricit*/ a material must have chargedparticles that are able to (lo%
@lectrol*te solutions all contain ions dissolved in the
%ater ionic compounds are electrol*tes because the* dissociate into
their ions %hen the* dissolve
>onelectrol*te solutions contain %hole moleculesdissolved in the %ater generall*/ molecular compounds do not ioniUe %hen the*
dissolve in %ater the notable eception being molecular acids
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Salt vs. Sugar Dissolved in Water
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ionic compounds
dissociate into ions %hen
the* dissolve
molecular compounds
do not dissociate %hen
the* dissolve
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$cids$cids are molecular compounds that io%i0e%hen the*
dissolve in %ater the molecules are pulled apart b* their attraction (or the %ater
%hen acids ioniUe/ the* (orm +=cations and also anions
'he percentage o( molecules that ioniUe varies (rom oneacid to another
$cids that ioniUe virtuall* 100# are called stro% !ci&s
+Cl;aq
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@lectrol*tes
$ strong electrol*tedissociates completel*%hen dissolved in %ater.
ionic compounds andstrong acids
$ %eaB electrol*teonl*dissociates partiall* %hendissolved in %ater.
%eaB acids
When compounds containing a pol*atomic ion dissolve/ the
pol*atomic ion sta*s together
+C!+:!;aq
4(
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Solubilit* o( )onic Compounds
Some ionic compounds/ such as >aCl/ dissolve ver*%ell in %ater at room temperature
ther ionic compounds/ such as $gCl/ dissolve
hardl* at all in %ater at room temperature Compounds that dissolve in a solvent are said to be so"$"e
Compounds that do not are said to be i%so"$"e
>aCl is soluble in %ater/ $gCl is insoluble in %ater the degree o( solubilit* depends on the temperature
even insoluble compounds dissolve/ ,ust not enough to bemeaning(ul
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When Will a Salt Dissolve&
redicting %hether a compound %ill dissolve in %ater is
not eas*
'he best %a* to do it is to do some eperiments to test
%hether a compound %ill dissolve in %ater/ then develop
some rules based on those eperimental results %e call this method the emiric!" metho&
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ractice Determine i( each o( the
(ollo%ing is soluble in %ater
T+
$g4r
CaCl!
b;>:
bSJ
T+ is soluble because it contains T=
$g4r is insolubleK most bromides are soluble/
but $g4r is an eceptionCaCl!is solubleK most chlorides are soluble/
and CaCl!is not an eception
b;>:
:
V
bSJis insolubleK most sul(ates are soluble/
but bSJis an eception
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recipitation 2eactions
Preciit!tio% re!ctio%s are reactions
in %hich a solid(orms %hen %e mi t%o
solutions the solid ;insoluble product< is called a
reciit!te
When one mies ions that (orm compounds
that are insoluble ;as could be predicted b*
the solubilit* guidelines
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//
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>o recipitate ?ormation H
>o 2eaction
T);aq< = >aCl;aq< TCl;aq< = >a);aq:;aq<
>a!S;aq< = CaCl!;aq<
/#
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Write the balanced chemical e5uation (or
the precipitation reaction bet%een an
a5ueous solution o( potassium carbonateand an a5ueous solution o( nicBel;))+J
solution o( b;C!+:!
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olecular @5uation
'he molecular e5uation lists the reactants and
products in their molecular (orm.
$g>:;aqet )onic @5uation
'o (orm the net ionic e5uation/ cross out an*thing thatdoes not change (rom the le(t side o( the e5uation to the
right.
'he onl* things le(t in the e5uation are those things that
change ;i.e./ react< during the course o( the reaction.
$g=;a5
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>et )onic @5uation
'o (orm the net ionic e5uation/ cross out an*thing thatdoes not change (rom the le(t side o( the e5uation to the
right.
'he onl* things le(t in the e5uation are those things that
change ;i.e./ react< during the course o( the reaction. 'hose things that didnAt change ;and %ere deleted (rom
the net ionic e5uation< are called spectatorions.
$g=;aq:9;aq
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Writing >et )onic @5uations
1. Write a balanced molecular e5uation.!. Dissociate all strong electrol*tes.
:. Cross out an*thing that remains unchanged (rom
the le(t side to the right side o( the e5uation.
J. Write the net ionic e5uation %ith the species thatremain.
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Write the complete ionic and net
ionic e5uation (or each
T!SJ;aq< = ! $g>:;aq< ! T>:;aq< = $g!SJ;sa!C:;aq< = ! +Cl;aq< ! >aCl;aq< = C!;g< = +!;la+;aq< >aCl;aq< = + ;laCl;aq< = +!;la+ solution that re5uires
!I." m3 to titrate "0.0 m3 o( 0.101" +!SJ&
G @ l i 2 ti
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Gas9@volving 2eactions Some reactions (orm a gas directl* (rom the ion
echange
T!S;aq< = +!SJ;aq
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>a+C:;aq< = +Cl;aq< >aCl;aq< = C!;g< = +!;la!S:;aq<
+!SJ;aq< = CaS;aq<
#(
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ther atterns in 2eactions
'he precipitation/ acid9base/ and gas9evolving reactions allinvolve echanging the ions in the solution
ther Binds o( reactions involve trans(erring electrons (rom
one atom to another these are called
o:i&!tio%;re&$ctio% re!ctio%s also Bno%n as redo reactions
man* involve the reaction o( a substance %ith !;ga;saCl;sa! >a=
= ! e
Cl!= ! e! Cl
'ro- Chemistr*- $ olecular $pproach/ !e
2 ti ( t l ith > t l
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2eactions o( etals %ith >onmetals
Consider the (ollo%ing reactions-J >a;sa!;sa;saCl;s< 'he reactions involve a metal reacting %ith a nonmetal
)n addition/ both reactions involve the conversion o((ree elements into ions
>a! P ! >a= !D
>aCl P >a= ClD
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id ti 2 d ti 2 ti
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re
ntice9
idation92eduction 2eactions
$n oidationoccurs%hen an atom or ionloseselectrons.
$ reductionoccurs%hen an atom or iongainselectrons.
ne cannot occur%ithout the other.
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re
ntice9
idation >umbers
'o determine i( an oidation9reduction reaction hasoccurred/ %e assign an oidation number to each element
in a neutral compound or charged entit*.
idation number ;oidation state< is a h*potheticalcharge assigned to the atom.
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re
ntice9
idation >umbers
@lements in their elemental (orm have an oidation
number o( 0.
'he oidation number o( a monatomic ion is the same
as its charge.
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re
ntice9
idation >umbers
>onmetals tend to have negative oidation numbers/
although some are positive in certain compounds or
ions.
*gen has an oidation number o( V!/ ecept in the peroideion in %hich it has an oidation number o( V1.
+*drogen is V1 %hen bonded to a metal/ =1 %hen bonded to a
nonmetal.
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re
ntice9
idation >umbers
>onmetals tend to have negative oidation numbers/
although some are positive in certain compounds or
ions.
?luorine al%a*s has an oidation number o( V1.'he other halogens have an oidation number o( V1 in most
binar* compoundsK the* can have positive oidation numbers/
ho%ever/ most notabl* in o*anions.
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re
ntice9
idation >umbers
'he sum o( the oidation numbers in a neutral
compound is 0.
'he sum o( the oidation numbers in a pol*atomic ion
is the charge on the ion.
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ractice roblems
Determine the o. XAs o( each element (or the (ollo%ing-
gCrJ
ClJ9
>!
?e>
nJ9
$ssign an oidation state to each
()
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$ssign an oidation state to each
element in the (ollo%ing
4r!
T=
3i?
C!
SJ!V
>a!!'ro- Chemistr*- $ olecular $pproach/ !e
id ti d 2 d ti
(1
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idation and 2eduction
$nother De(inition idation occurs %hen an atomAs oidation state increases
during a reaction
2eduction occurs %hen an atomAs oidation state decreases
during a reaction
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idation2eduction(
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idation 2eduction idation and reduction must occur simultaneousl*
i( an atom loses electrons another atom must taBe them 'he reactant that reduces an element in another
reactant is called the re&$ci% !e%t
the reducing agent contains the element that is oidiUed
'he reactant that oidiUes an element in another
reactant is called the o:i&i0i% !e%t
the oidiUing agent contains the element that is reduced
! >a;s< = Cl!;g< P ! >a=Cl;sa is oidiUed/ Cl is reduced
>a is the reducing agent/ Cl!
is the oidiUing agent'ro- Chemistr*- $ olecular $pproach/ !e
$ssign oidation states then determine the
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$ssign oidation states/ then determine the
element
oidiUed and reduced/ and determine theoidiUing agent
and reducing agent in the (ollo%ing reaction-?e = nJ
V= J +=P ?e:= = n! = ! +!
SnJ== Ca P Sn!= = Ca!=
? = S P S?