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Chapter 18:Solubility and

Simultaneous Equilibria

Chemistry: The Molecular Natureof Matter, 6E

Jespersen/Brady/Hyslop

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Jespersen/Brady/HyslopChemistry:TheMolecularNature ofMatter,6E

Solubility of Salts

Precipitation reactions (C !"

Exchange reactions in which one product is water

insoluble compound CaCl2 (l ! "a2C#$ (aq CaC#$ (s ! 2 "aCl (aq

#nsoluble compoun$

Compound ha%ing water solubility o& less than '')mole o& dissol%ed material per liter o& solution

S * '') +

2

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Solubility of Salts Ch ! Solubility %ules

,uidelines &or what is insoluble

-oesn.t mean compound won.t dissol%e at all Just not %ery much

No& &ant to

uantitate solubilities Explore conditions under which some compounds

precipitate and others don.t

0pplications in separation o& ions Especially toxic metal ions such as Hg2!1 l$!1 3$!1 etc

$

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'hy Stu$y Solubility ooth decay

0cids &rom &oods dissol%e enamel1 4Ca5(6#7$#H8 9hydroxyapatite

:educed by &luoride which replaces #H; to &orm&luorapatite 9 4Ca5(6#7$

?@ray o& upper and lower gastrointestinal tract Clari&ied by barium sul&ateA%ery insoluble

BaS#7 toxic1 but sa&e1 as it doesn.t dissol%e

7

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Solubility E)uilibria Solids in equilibrium with ions in solution

hen ionic salt dissol%es in water

0ssume dissociates into separate hydrated ions >nitially1 no ions in solution

Ca*+ (s" Ca+ (a)" + *- (a)"

0s dissolution occurs1 ions build up and collide Ca+ (a)" + *- (a)" Ca*+ (s"

0t Equilibrium

Ca*+ (s" Ca+ (a)" + *- (a)"

"ow ha%e saturated solution

5

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Solubility an$ Solubility Pro$uctSolubility

0mount o& salt that dissol%es in gi%en amount o&

sol%ent to gi%e saturated solution

Concentration >n&inite number o& %alues

Solubility pro$uct 6roduct o& molar concentrations o& ions in saturated

solution raised to appropriate powers

Equilibrium constant

#nly one %alue &or gi%en solid at gi%en temperatureTemperature $epen$ence

Solubilities and thus Csp change with

D

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Solubility of Salts Consider 0gCl in water

#nly a %ery small amount dissol%es

Equilibrium exists when solution is saturated ./Cl(s" ./(a)" Cl-(a)"

Equilibrium law

0sp 2./32Cl-3

0sp solubility pro$uct constant

Solubility equilibrium

:e&lects solubility o& compound

6roduct o& ion concentrations

F

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Solubility an$ Solubility Pro$uct Solubility

0mount o& salt that dissol%es in gi%en amount o&sol%ent to gi%e saturated solution

Solubility pro$uct 6roduct o& molar concentrations o& ions in

saturated solution raised to appropriate powers

Temperature $epen$ence Solubilites and thus Csp change with temperature

Table 1841 Solubility product constants at 25 GC

+ore in able CD (0ppendix p 075

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#on Pro$uct 5s4 Solubility Pro$uct

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'ritin/ 0sp E)uilibrium 9a&s

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Calculation usin/ 0sp an$ Molar

SolubilitiesMolar solubility

+oles o& salt dissol%ed in one liter o& saturatedsolution

0ssume what little dissol%ed1 dissociates )''L

0ssumes there is somesolid uantity is not important

Solid is not included in mass action expression

.4 i5en Solubilites, Calculate 0sp74 i5en 0sp, Calculate Solubility

))

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.4 i5en Solubilites , Calculate 0spE 140t 25 GC1 the solubility o& 0gCl is )$7 x)';5 + Calculate the solubility product &or 0gCl

./Cl (s"

./

(a)" Cl-

(a)"0sp 2./

32Cl-3

Csp 9 ()$7 x )';5()$7 x )';5

Csp

9148; 1;-1;

./Cl (s" ./ (a)" Cl- (a)"

> ''' ' ''

C

E

14

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>our Turn?

he solubility o& a salt1 02B$1 is &ound to be$')';5 +4 hat is the %alue o&CspM

0 2D x )'@2)

B 57 x )'@K

C 27 x )'@2$

- )F x )'@2)

02B$ 20$! ! $B2@

408 9 2($' x )'@5

4B8 9 $($' x )'@5

9 40824B8$ 9 (D' x )'@52(K' x )'@5$

9 2D x )'@2)

)$

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74 i5en 0sp, Calculate Solubility

E4 + hat is the molar solubility o& Cu> inwaterM hat are the equilibrium

concentrations o& Cu!

and >;

MStep 14 'rite balance$ e)uation for

$issociation of salt

Cu# (s" Cu (a)" #- (a)"

Step +4 'rite e)uilibrium la&

0sp 2Cu

32#-

3Step

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E4 + Molar Solubilities from 0sp

Step =4 Concentration Table

Step !4 Plu/ into an$ sol5e 0sp epression

Csp 9 ' )'; 9 (x(x

x2 9 ' )'; 9 +48 1;-= M 9 calculated molar solubility

o& Cu> 2Cu3 2#- 3

Conc (+ Cu# (s" Cu (a)" #- (a)"

>nitial ''' ' ''Change

Equil.m

+x+x

xx

x

)5

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Molar Solubility an$ 0sp Problems

Strategy &or sol%ing

) rite balanced equation &or dissociation o& salt

2 rite equilibrium law

$( Csp &or salt (&rom table

7 Concentration table

5a Sol%e &or x 9 solubility

#r

5b ,i%en solubilities1 calculate Csp

)D

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.4 i5en Solubilites , Calculate 0spE4 < Calculate Csp &or Bi2S$ gi%en solubility is

)' x )';)5 + at 25 GC

Step 14 'rite balance$ e)uation for$issociation of salt

7i+S< (s" + 7i

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.4 i5en Solubilites , Calculate 0sp

7i+S< (s" + 7i+ (a)" < S+- (a)"

> ("o entries ''' '''

C in this

E column

+3(1.0 105 )+2(1.0 1015)

3.0 10152.0 1015

Ksp = (2.0 x 1015)2(3.0 x 1015)3

Ksp = (4.0 x 1030)(27 x 1045)

Ksp = 1.1 x 1073

Step =4 Sol5e for 0sp

)

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74 i5en 0sp, Calculate Solubilities

E4 = Calculate the solubility o& Canitial ("o entries ''' '''

Change in this

Equil.m column

+

+)K

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E4 = Molar Solubilities from 0sp

Step

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>our Turn?

,i%en Csp 9 )7 x )';F &or Cu(>#$21 calculatethe solubility o& this salt

0 52 x )'@$

B $$ x )'@$

C 2D x )'@7

- $F x )'@7

Cu(>#$2 (s Cu2!

! 2>#$@

sp 9 )7 x )'@F 9 s (2s2

s 9 $$ x )'

2)

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>our Turn?hat is the molar solubility o& 0g$6#7 in waterM hat

is the molar concentration o& each ion in solutionMCsp 9 K )'

;)F

0 57 x )'@K 40g!8 9 57 x )'@K 46#7$@8 9 57 x )'@K

B 7$ x )'@5 40g!8 9 )$ x )'@7 46#7$@8 9 7$ x )'@5

C 57 x )'@K 40g!8 9 )D x )'@ 46#7$@8 9 57 x )'@K

-KF x )'@F 40g!8 9 2F x )'@7 46#7$@8 9 KF x )'@F

0g$6#7 (s $0g! ! 6#7

$@

sp 9 K x )'@)F 9 40g846#8 9 ($s$(s

s 9 7$ x )'40g!8 9 $s 9 )$ x )'@7 +

46#7$@8 9 s 9 7$ x )'@5 +

22

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>our Turn?hat is the solubility o& 6bCl2 in grams per )''' m=

at 25o M sp 9 )F x )'@5

0 '5D g

B 'F2 g

C '75 g

- '$K g

6bCl2 (s 6b2! ! 2Cl@

sp 9 )F x )'@5 9 46b2!84Cl@82 9 s (2s2

s 9 )D2 x )'@5

+()D2 x )'@5 mol/= x (2F)) g/mol x ') = 9 '75 g

in )'' m=

2$

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%elati5e SolubilitiesCsp gi%es in&ormation about solubility o& salts +ust be care&ul when comparing relati%e

solubilities

wo possible cases when comparing

) +ust compare salts that contain the same number

o& ions0g>(s Csp 9 )5 x )'

;)D

Cu>(s Csp 9 5' x )';)2

CaS#7(s Csp 9 D) x )';5

Each salt dissol%es to produce 2 ions

Salt cation ! anion

Csp

9 4cation84anion8

27

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%elati5e Solubilities

) +ust compare salts that contain the same numbero& ions

>& solubility 9 x

hen 4cation8 9 4anion8 9 x

Csp 9 x2

So can compare solubilities by comparing Csp.s

CaS#7 * Cu> * 0g>

most soluble least solublelargest Csp smallest Csp

solubilityx sp ==

25

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%elati5e Solubilities

2 Compare salts with di&&erent number o& ions Each produces di&&erent number o& ions

Each uses di&&erent Csp

expression

"o way to predict relati%e solubility based on Csp Bi2S$ * 0g2S * CuS+ost soluble least soluble

2D

Salt 0 sp Aions CalcB$Solubility (M"

CuS 5 x )';75

2 K2 x )';2$

0g2S )D x )';7K $ $7 x )';)F

Bi2S$ )) x )';F$ 5 )' x )';)5

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Common #on Effect 3p until now all calculations in pure water hat happens i& > add another salt to a solution

containing one o& the ions in our insoluble saltM

Consider Pb#+(s" Pb+(a)" +#-(a)"

Saturated solution o& 6b>2 in water

6b>2 (yellow solid precipitates out

'hy

=e Chatelier.s 6riniciple

0dd product >;

Equilibrium mo%es to le&t and solid 6b>2 &orms

2F

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Common #on Effect Common ion

>on in solution that is supplied by more than one

solute

Common #on Effect

=owering o& solubility o& ionic compound by

addition o& common ion

2

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E4 ! Common #on Effect

0 hat is the molar solubility o& 0g2Cr#7 in')'+ 0g"#$ solutionM Csp 9 K' )'

;)2

B hat is the molar solubility o&0g2Cr#7 in pure waterM

C hat is the molar solubility o&

0g2Cr#7 in ')'' + "a2Cr#7M

0g2Cr#7(s 20g!(aq ! Cr#7

2;(aq

sp 9 40g!824Cr#7

2;8 9 K' )';)2

2K

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.4 +olar solubility o& 0g2Cr#7 in ')'+ 0g"#$solutionM Csp 9 K' )'

;)2

Csp 9 K' )';)2 9 (')'+24x8

x 9 Solubility o& 0g2Cr#7 9 K' )';)' +

40g!8 9 ')' +

4Cr#7

2;8 9 K' )';)' +

')''(

)''Kx

)2

=

./+Cr=(s" +./(a)" Cr=

+-(a)"

> ("o entries ')' + '''

C in this

E column

+x+2x

x#0.10

$'

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74 Solubility o& 0g2Cr#7 in pure water./+Cr=(s" +./

(a)" Cr=+-(a)"

> ("o entries ''' + ''' +C in this

E column

+x+2x

x2x

Ksp = [Ag+]2[CrO4

2] = (2x)2(x) = 9.0 1012 = 4x3

$ )2$)2

)'252

7

)''Kx

=

=

? 9 Solubility o& 0g2Cr#7 9 )$) )';7 +

4Cr#72;8 9 x 9 )$) )';7 +

40g!

8 9 2x 9 2D2 )';7

+ $)

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C4 Solubility o& 0g2Cr#7 in ')'' + "a2Cr#7M./+Cr=(s" +./

(a)" Cr=+-(a)"

> ("o entries ''' + ')' +C in this

E column

+x+2x

2x #0.10

Ksp = (2x)2(0.10) = 9.0 1012 = 4x2(0.10)

)))2

)'252

7'

)''Kx

=

=

x 9 Solubility o& 0g2Cr#7 9 7F )';D +

4Cr#72;8 9 x 9 7F )';D +

40g!

8 9 2x 9 K5 )';D

+ $2

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$$

C4 Solubility o& 0g2Cr#7 in ')'' + "a2Cr#7M./+Cr=(s" +./

(a)" Cr=+-(a)"

> ("o entries ''' + ')' +C in this

E column + D;41;

Csp 9 (2x2(')' 9 K' )';)2 9 7x2(')'

)))2

)'252

7'

)''Kx

=

=

x 9 Solubility o& 0g2Cr#7 9 7F )';D +

4Cr#72;8 9 x 9 7F )';D +

40g!8 9 2x 9 K5 )';D +

+x+2x

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>our Turn?

hat e&&ect would adding copper(>> nitrateha%e on the solubility o& CuSM

0 he solubility would increase

B he solubility would decrease

C he solubility would not change

$7

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>our Turn?

he molar solubility o& 6b

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Pre$ictin/ if Precipitate &ill *orm

>n maIing a solution containing %arious ions1will the salt precipitate at the gi%enconcentrationsM

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Pre$ictin/ if Precipitate &ill *orm

$

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Pre$ictin/ Precipitation

E4 6 -oes a precipitate o& 6b>2 (sp9)7 x )'

&orm i& )''' m= o& ''5'' + 6b("#$2 are mixed

with 2'''m= o& ' )'' + "a>MPb#+(s" Pb

+(a)" +#-(a)"

Csp 9 46b2!84>;82 9 )7 )';

Strate/y for sol5in/

) Calculate concentrations in solution to be prepared

2 Calculate 8sp 9 46b2!

84>;

82

$ Compare 8sp to 0sp

$K

E 6 P $i ti P i it ti

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E4 6 Pre$ictin/ Precipitation

Step 14 Calculate concentrations Here diluting )'' m= to $''m=

total 9 )''' m= ! 2''' m= 9 $''' m=

46b2!8o 9 )DF )';2 +

4>;8 9 DDF )';2 +

m=

m=mmolm=

'$''

/)'''('2''(

solutiono&m=

>o&mmol8>4 ==

m=

m=mmolm=

'$''

/'5'''(')''(

solutiono&m=

6bo&mmol86b4

22 ==

++

7'


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Step +4 Calculate 8sp 8sp 9 46b

2!84>;82 9 ()DF)';2 +(DDF)';2 +2

8sp 9F7$ )';5

Step 2 :eaction essentially goes to completion

7)


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>& reaction goes essentially to completion1 whatwill &inal equilibrium concentrations beM

) -o stoichiometric calculations &or precipitate

&ormation2 hen do equilibrium calculations to determine ion

concentrations in solution

Step 14 Stoichiometric CalculationPb+(a)" +#- (a)" Pb#+(s"

Be&ore

rxn

()''m=(''5''+

9 5'' mmol

(2''m=(')''+

9 2''' mmol

"o e&&ect on Csp

0&ter:xn

!4;; - !4;; ;4;; mmol

+;4;; - +(!4;;"

1; mmol

72


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Step +4 System at equilibrium Some small amount o& 6b>2 redissol%es to &orm

equilibrium 46b2!8

Basically a common ion problem

Pb#+(s" Pb+(a)" +#-(a)"

>nitial conc.ns ''' )''mmol/$''m=

9 $$$ x )';2 +

Equilibriumconc.ns

$$$ x )';2 + ! 2xP $$$ x )';2 +

!x

Csp 9 )7 )'; 9 46b2!84>-82 9 (x($$$ x )';22

86b4)'$)

)'$$$(

)'7)x 25

22

+

==

= +

7$

E 6 Pre$ictin/ Precipitation

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$$$ x )';2 + ** 2x1 so approximation %alid

; in )''' m= o& ''5'' + 6b("#$2 mixedwith 2'''m= o& ' )'' + "a>

2#-3

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E4 F Pre$ictin/ Precipitation

Suppose you mix )''' m= o& '2'' + BaCl2with 5'' m= o& ''$'' + "a2S#7 illBaS#

7

(sp

9 )) )';)' precipitateM

7aS=(s" 7a+(a)" S=

+-(a)"

sp 9 4Ba2!84S#7

2;8

Step 14 Calculate concentrations

4Ba2!8 9 ')$$ +

m=

m=

mol

mol+

')5'

')''

BaCl)

Ba)BaCl2'''8Ba4

2

2

22 =

++

75

E F Pre$ictin/ Precipitation

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E4 F Pre$ictin/ Precipitation

4S#72;8 9 '')'' +

Step +4 Calculate 8sp 8sp 9 4Ba

2!84S#72;8 9 (')$$('')''

8sp 9 )$$

)';$

Step

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p an$ Solubility

M/("+(s" M/+(a)" +-(a)" #H; shi&t equilibrium to le&t

0dd H! shi&t equilibrium to right

=e Chatelier.s 6rinciple

./

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>our Turn?

hat is the molar solubility o& 6b>2 in purewaterM sp 9 K x )'

@K

0 2) x )'@$

B )F x )'@$

C 7K x )'@5

- )7 x )'@$

6b>2(s 6b2! ! 2>@

9 K) x )' 9 46b

2!

84>

@

8 9 s (2s

2

s 9 )7 x )'@$+

7

>our Turn?

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>our Turn?

hat is the molar solubility o& 6b>2 in '2'+"a> solutionM Csp 9 FK )'

;K

0 $K x )'@)'

B 27 x )'@F

C D) x )'@K

- 27 x )'@F

6b>2(s 6b2! ! 2>@ 4>@8 9 '2'+

9 FK x )'

@K

9 46b

2!

84>

@

8

2

9 46b

2!

8('2'

2

46b2!8 9 27 x )'@F+

+olar solubility 9 46b2!8 9 27 x )'@F+

7K

>our Turn?

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>our Turn?

hat is the molar solubility o& 6b>2 in '2'+6b("#$ solutionM Csp 9 FK )'

;K

0 7K x )'@

B $F x )'@$

C )) x )'@7

- 22 x )'@7

6b>2(s 6b2! ! 2>@ 4>@8 9 '2'+

9 FK x )'

@K

9 46b

2!

84>

@

8

2

9 ('2' 4>

@

8

2

4>@8 9 22 x )'@7+

+olar solubility 9 )/2 4>@8 9 )) x )'@7+

5'

>our Turn?

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>our Turn?

;M

0 0dding 6b2! increases the solubility o& 6b>2more than >@

B 0dding >@

decreases the solubility o& 6b>2more than 6b2!

C 0dding 6b2! decreases the solubility o&

6b>2 more than >@- hey both ha%e the same e&&ect on the

solubility o& 6b>2

5)

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Solubility and SimultaneousEquilibria

6art 2

Metal i$es @n$er/o %eaction

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Metal i$es @n$er/o %eaction

&ith 'ater

5$

3sually ignore reaction o& ionic solid with water

>& the anion o& a salt is %ery basic1 a subsequent

reaction o& the anion with water occurs Such is the case o& many metal oxides

0b &or #2; 9 ) R)'22

So 0g2# actually dissociates to &orm 0g! and #H;

0sp%alue listed taIes this subsequent reaction into account

0g2#(s

20g!

(aq ! #2;

(aq 0sp#2;(aq ! H2# 2#H

;(aq 0b0g2#(s ! H2# 20g

!(aq ! 2#H;(aq 0net

Metal Sulfi$es .lso @n$er/o %eaction

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Metal Sulfi$es .lso @n$er/o %eaction

'ith 'ater

57

Sul&ide ion (S2; is also %ery basic

-oesn.t exist in aqueous solution

+etal sul&ides also undergo a subsequentreaction with water

0g2S(s 20g!(aq ! S

2;(aq 0sp

S2;(aq ! H2# #H; (aq ! HS;(aq 0b

0g2S(s ! H2# 20g!(aq ! #H;(aq ! HS; (aq0net

.ctual 0sp 940g!824#H;84HS;8

Most 'aterG#nsoluble Metal i$es

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H! reacts with #2; to produce H2#

:eleases metal ion &rom solid

:ecall that oxide ion is too power&ul a base to exist inaqueous solution

E4

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Sul&ur is below oxygen in ,roup >00s a result1 metal sul&ides are similar to

metal oxides

S2; (liIe #2; is too strong o& a base to exist inwater

Sul&ides dissol%e by reacting with waterE4 "a2S(s ! H2# 2"a

!(aq ! HS;(aq ! #H;

(aq

5D

7asic Salts .re More Soluble #n

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7asic Salts .re More Soluble #n

.ci$s

5F

Subsequent reactions assist the solubility o& solids

>& anion o& salt is basic1 it will react in acidic

solution to dissol%e more &ully "et reaction o& such dissolutions is called Cspa

nS(s

n

2!(aq

! S

2;(aq

0spS2;(aq ! H!(aq HS;(aq 1I0a+HS; (aq ! H! (aq H2S (g 1I0a1

nS(s ! 2H!(aq n2!(aq ! H2S(aq 0spa

0spa (acidic an$ 0sp (basic are listed in able )2

9earnin/ ChecJ

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ea / C ec

5

hat is the molar solubility o& BaC#$ in $' +HClM

Csp BaC#$ 9 5' x )'TK

H2C#$ Ca) 9 7$ x )'TF a2 9 7F x )'

T))

7aC

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+etal sul&ides can &orm Some metal ions are so reacti%e that they react

with H2S directly

hese acti%e ions include Cu2!1 6b2!1 and "i2!

0 typical reaction is

Cu2!(aq ! H2S(aq CuS(s ! 2H!(aq

=arge %alue o& Cindicates that

Equilibrium lies &ar to right

#nly &orward reaction important

Sul&ides require closer in%estigation

5K

Documents

chpt18.pdf