Chapter 4: Chemical Quantities and Aqueous Reactions

7/13/2019 Chapter 4: Chemical Quantities and Aqueous Reactions

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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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'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&

'ro- Chemistr*- $ olecular $pproach/ !e


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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&


What )s the molarit* o( a solution containing :.J g o(

>+: in !00.0 m3 o( solution&

33


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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


or


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What volume o( 0.1!" >a+ ;in 3iters< contains

a total o( 0.!"" mol o( >a+&


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" +!&


+o% %ould *ou prepare !"0.0 m3 o( 0.1"0

CaCl!&

3


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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&


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&

3'


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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


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


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


/3


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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.

4


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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


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


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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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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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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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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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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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


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

(3


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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?

Chapter 4: Chemical Quantities and Aqueous Reactions

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Transcript of Chapter 4: Chemical Quantities and Aqueous Reactions