Brdy 6Ed Ch18 Solubility

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    Chapter 18:Solubility and

    Simultaneous Equilibria

    Chemistry: The Molecular Nature

    of Matter, 6E

    Jespersen/Brady/Hyslop

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Solubility of Salts

    Precipitation reactions (C !" Exchange reactions in which one product is water

    insoluble compound

    CaCl2 (l! "a2C#$ (aqCaC#$ (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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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 compoundsprecipitate 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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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 temperature

    Temperature $epen$ence Solubilities and thus Cspchange 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 law0sp 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 Cspchange 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/ 0spE)uilibrium 9a&s

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    Calculation usin/ 0span$ Molar

    Solubilities

    Molar solubility +oles o& salt dissol%ed in one liter o& saturated

    solution

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

    0ssumes there is somesolid uantity is not important

    Solid is notincluded 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

    Csp9 ()$7 x )';5()$7 x )';5

    Csp9148; 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

    $'M)';5 +4 hat is the %alue o&CspN0 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> in

    waterN hat are the equilibriumconcentrations o& Cu!and >;N

    Step 14 'rite balance$ e)uation for

    $issociation of saltCu#(s" Cu(a)" #-(a)"

    Step +4 'rite e)uilibrium la&

    0sp 2Cu32#-3

    Step

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    E4 +Molar Solubilities from 0spStep =4 Concentration Table

    Step !4 Plu/ into an$ sol5e 0spepression

    Csp9 ' )';9 (x(x

    x29 ' )';

    9 +48

    1;-= M9 calculated molar solubilityo& 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$ 0spProblems

    Strategy &or sol%ing

    ) rite balanced equation &or dissociation o& salt

    2 rite equilibrium law

    $( Csp&or salt (&rom table

    7 Concentration table

    5aSol%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 GCStep 14'rite balance$ e)uation for

    $issociation of salt

    7i+S

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    .4 i5en Solubilites , Calculate 0sp

    7i+S

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    74i5en 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 Csp9 )7 x )'

    ;F&or Cu(>#$21 calculate the

    solubility o& this salt

    0 52 x )'@$

    B $$ x )'@$

    C 2D x )'@7

    - $F x )'@7

    Cu(>#$2(s Cu2! ! 2>#$

    @

    sp9 )7 x )'@F9 s (2s2

    s 9 $$ x )' 2)

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?hat is the solubility o& 6bCl2in grams per )''' m=

    at 25o

    N sp9 )F x )'@5

    0 '5D g

    B 'F2 g

    C '75 g- '$K g

    6bCl2(s 6b2! ! 2Cl@

    sp9 )F x )'@59 46b2!84Cl@829 s (2s2

    s 9 )D2 x )'@5 +

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

    2$

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    %elati5e Solubilities) +ust compare salts that contain the same number

    o& ions >& solubility 9 x

    hen 4cation8 9 4anion8 9 x

    Csp9 x2

    So can compare solubilities by comparing Csp.s

    CaS#7* Cu> * 0g>

    most soluble least soluble

    largest Csp smallest Csp

    solubilityCx sp ==

    25

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    %elati5e Solubilities2 Compare salts with di&&erent number o& ions

    Each produces di&&erent number o& ions

    Each uses di&&erent Cspexpression

    "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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Common #on Effect 3p until now all calculations in pure water

    hat happens i& > add another salt to a solutioncontaining one o& the ions in our insoluble saltN

    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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Common #on Effect Common ion

    >on in solution that is supplied by more than onesolute

    Common #on Effect

    =owering o& solubility o& ionic compound byaddition o& common ion

    2

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 ! Common #on Effect

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

    ')'+ 0g"#$solutionN Csp9 K' )';)2

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

    C hat is the molar solubility o&0g2Cr#7in ')'' + "a2Cr#7N

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

    2;(aq

    sp9 40g!824Cr#7

    2;8 9 K' )';)2

    2K

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    ff

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 ! Common #on Effect74Solubility o& 0g2Cr#7in 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

    )'25(27

    )''(K

    x

    =

    =

    ? 9 Solubility o& 0g2Cr#79 )$) )';7+

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

    40g!8 9 2x 9 2D2 )';7+ $)

    ff

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 ! Common #on EffectC4 Solubility o& 0g2Cr#7in ')'' + "a2Cr#7N

    ./+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

    )'25(27('

    )''(K

    x

    =

    =

    x 9 Solubility o& 0g2Cr#79 7F )';D+

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

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

    E ! C # Eff

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 ! Common #on Effect

    $$

    C4 Solubility o& 0g2Cr#7in ')'' + "a2Cr#7N

    ./+Cr=(s" +./(a)" Cr=+-(a)"> ("o entries ''' + ')' +

    C in this

    E column + D;41;

    Csp9 (2x2(')' 9 K' )';)29 7x2(')'

    )))2

    )'25(27('

    )''(K

    x

    =

    =

    x 9 Solubility o& 0g2Cr#79 7F )';D+

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

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

    +x+2x

    > T ?

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?hat e&&ect would adding copper(>> nitrate

    ha%e on the solubility o& CuSN0 he solubility would increase

    B he solubility would decrease

    C he solubility would not change

    $7

    > T ?

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?he molar solubility o& 6b

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Pre$ictin/ if Precipitate &ill *orm

    >n maIing a solution containing %arious ions1

    will the salt precipitate at the gi%enconcentrationsN

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Pre$ictin/ if Precipitate &ill *orm

    >n maIing a solution containing %arious ions1

    will the salt precipitate at the gi%enconcentrationsN

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Pre$ictin/ if Precipitate &ill *orm

    $

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    E 6 P $i ti P i it ti

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 6 Pre$ictin/ Precipitation >& reaction goes essentially to completion1 what

    will &inal equilibrium concentrations beN

    ) -o stoichiometric calculations &or precipitate&ormation

    2 hen do equilibrium calculations to determine ion

    concentrations in solutionStep 14 Stoichiometric Calculation

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

    Be&orerxn

    ()''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

    E 6 P e$ictin/ P ecipitation

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 6 Pre$ictin/ PrecipitationStep +4 System at equilibrium

    Some small amount o& 6b>2redissol%es to &ormequilibrium 46b2!8

    Basically a common ion problem

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

    >nitial conc.ns ''' )''mmol/$''m=9 $$$ x )';2+

    Equilibrium

    conc.ns

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

    !x

    Csp9 )7 )';9 46b2!84>-829 (x($$$ x )';22

    86b4)'$)

    )'$$$(

    )'7)x 25

    22

    H+

    ==

    = +

    7$

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    E F Pre$ictin/ Precipitation

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 F Pre$ictin/ Precipitation

    Suppose you mix )''' m= o& '2'' + BaCl2

    with 5'' m= o& ''$'' + "a2S#7 illBaS#7(sp9 )) )'

    ;)' precipitateN

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

    +-(a)"

    sp9 4Ba2!84S#7

    2;8

    Step 14Calculate 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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    E4 F Pre$ictin/ Precipitation

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

    Step +4 Calculate 8sp8sp9 4Ba

    2!

    84S#72;

    8 9 (')$$('')'' 8sp9 )$$ )'

    ;$

    Step

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?hat is the molar solubility o& 6b>2in pure

    waterN sp9 K x )'@K

    0 2) x )'@$

    B )F x )'@$

    C 7K x )'@5

    - )7 x )'@$

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

    9 K) x )' 9 46b2!84>@8 9 s (2s2

    s 9 )7 x )'@$+

    7

    >our Turn?

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?hat is the molar solubility o& 6b>2in '2'+"a>

    solutionN Csp9 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 )'@K9 46b2!84>@829 46b2!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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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?hat is the molar solubility o& 6b>2in '2'+

    6b("#$ solutionN Csp9 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 )'@K9 46b2!84>@829 ('2' 4>@82

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

    +olar solubility 9 )/2 4>@8 9 )) x )'@7+5'

    >our Turn?

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    >our Turn?;N

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

    more than >@

    B 0dding >@decreases the solubility o& 6b>2

    more 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 Simultaneous

    Equilibria

    6art 2

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

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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 ) M)'22

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

    0sp%alue listed taIes this subsequent reaction into account

    0g2#(s20g!(aq! #2;(aq 0sp

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

    0g2#(s! H2# 20g!(aq! 2#H;(aq 0net

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

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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 subsequent

    reaction with water0g2S(s 20g

    !(aq ! S2;(aq 0sp

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

    0g2S(s! H2# 20g!(aq! #H;(aq! HS;(aq0net.ctual 0sp940g

    !824#H;84HS;8

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    *ormation of #nsoluble Metal Sulfi$es

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    Sul&ur is below oxygen in ,roup >0

    0s a result1 metal sul&ides are similar tometal oxides S2;(liIe #2; is too strong o& a base to exist in

    water Sul&ides dissol%e by reacting with water

    E4 "a2S(s! H2# 2"a!(aq! HS;(aq! #H;(aq

    *ormation of #nsoluble Metal Sulfi$es

    5D

    7asic Salts .re More Soluble #n

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    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 n2!(aq ! S2;(aq 0sp

    S2;(aq! H!(aqHS;(aq 1I0a+

    HS;

    (aq! H!

    (aq

    H2S

    (g 1I0a1nS(s! 2H!(aqn2!(aq ! H2S(aq 0spa

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

    9earnin/ ChecJ

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    Jespersen/Brady/HyslopChemistry:TheMolecularNatureofMatter,6E

    9earnin/ ChecJ

    5

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

    HClN CspBaC#$9 5' x )'

    UK

    H2C#$ Ca) 9 7$ x )'UFa2 9 7F x )'

    U))

    7aC

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    %eaction of Metal ions &ith S +etal sul&ides can &orm

    Some metal ions are so reacti%e that they reactwith 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