Precipita;on,•  Example(7:(Calculate(the(minimum(mass(of(Na2CO3(that(must(be(added(to(10.0(L(of(1.5(x(10@3(M(CaCl2(to(start(the(precipitation(of(CaCO3(

•  Example(8:(Calculate(the(minimum(mass(of(FeBr3(that(must(be(added(to(500.(mL(of(2.5(x(10@4(M(of(AgNO3(to(start(the(precipitation(of(AgBr.(

(

86(

fmin [Coz"] ← Use Q (cacao)

Ksp Ca coz = 5.0×10 - 9 (Chl 12booklet)zt

Eca] = 1.5×10-3M

[cost] = Ksp ÷ [CAZ'T =3 .5×10-6M = [Nazcos]

XIO. 0L↳ 105-99 9h013.5×10-327-7[Agt]

Ksp Ag Br = 5.4 E -13 = [Agt] [Br][Br -] = Ksp :-[Agt] = 2.16×10 -9M Febres → Fe3tt3Br

-

[Febres ] = [Br -I ÷ 3 = 172×10- 'OM

µ295.5591M01

Mass FEBV 3 = [Febres] x 500 .

XD-3mL X MM CFE Brs)

= t.li/lO-7gFeBr3J

AP(Chemistry(12(

Solubility(and(Complex(Ion(Equilibria(

Qualitative(Analysis(and(Selective(Precipitation(

89(

Qualita;ve,Analysis,

•  In(analytical(chemistry,(aqueous(solutions(are(often(analysed(for(the(presence(of(speci?ic(ions.(Once(the(ion(is(con?irmed(to(be(presence,(the(ion(can(be(separated(if(necessary(

•  Because(different(substances(have(different(solubilities,(we(can(achieve(the(two(goals(above(as(follows:(

1.  We(can(use(the(presence(of(a(precipitate(to(con?irm(the(presence(of(an(ion(

2.  We(can(separate(ions(by(precipitating(them(selectively(

90(

Qualita've*Analysis*•  Suppose'you'are'analyzing'a'solution'for'the'following'cations:'Ag+'and/or''Ca2+.''!!There!are!4!possible!cases.!

•  If'we'add'____________to'the'solution,'then'the'formation'of'a'precipitate'will'con@irm'the'presence'of'____________in'the'solution'

•  Suppose'we'add'____________to'to'the'solution'instead.'The'formation'of'a'precipitate'con@irms'that'_______________________!present,'but'does'not'tell'us'which' 91'

Case!1! Case!2! Case!3! Case!4!

Ag+'and''Ca2+'' Ag+'only' Ca2+only' Neither'ion'Add'Add'

④ AgtionAgclcs) Caclzcag )

NaCl PPT PPT No PPT no PPT

Narcos PPT PPT PPT no PPT

NA2CO3

either Agtorcaztp's

AgzC03CS ) Ca 3G )

Qualita;ve,Analysis,

•  Therefore,(we(should(test(for(Ag+(?irst(by(adding(NaCl.(If(any(precipitates(form,(we(can(?ilter(them(out,(and(test(the(?iltrate((the(remaining(solution)(with(Na2CO3.(

•  Here(is(the(strategy:(! If(a(precipitate(forms(from(adding(NaCl,(but(not(Na2CO3,(then(only(Ag+(is(present((

! If(a(precipitate(does(not(form(when(adding(NaCl,(but(does(when(adding(Na2CO3,(then(only(Ca2+(is(present(

! If(a(precipitate(forms(when(adding(NaCl,(the(solution(is(?iltered,(and(then(another(precipitate(forms(when(adding(Na2CO3,(then(both(Ag+(and(Cu2+(are(present(

92(

Qualita;ve,Analysis,

•  Here(is(the(experimental(procedure(to(analyze(the(presence(of(Ag+(and/or(Ca2+(qualitatively.(1.  Add(NaCl(to(the(solution(2.  If(any(precipitates(forms,(?ilter(the(precipitate(and(

keep(both(the(?iltrate(and(residue.(The(precipitate(con?irms(the(presence(of(Ag+.(

3.  Add(Na2CO3(to(the(?iltrate((or(starting(solution(if(no(precipitate(formed(in(step(1)(

4.  If(any(precipitate(forms,(the(presence(of(Ca2+(is(con?irmed.(

"'In'other'words,'_irst'add'soluble'salt'that'is'known'to'form'PPT'with'only'one'of'the'suspect'cation.'

93(

* @ *

Qualita;ve,Analysis,•  If(we(were(to(provide(a(procedure(to(separate'the'cations,'Ag+(and(Ca2+,(it(would(be(as(follows:(1.  Add(NaCl(to(the(solution(to(form(the(precipitate(

AgCl(s)(2.  Filter(the(precipitate((AgCl)(and(set(it(aside(3.  Add(Na2CO3(to(the(?iltrate(to(form(the(precipitate(CaCO3(s)(4.  Filter(the(precipitate(CaCO3(and(set(it(aside(

•  Notice'that'even'though'we'have'already'separated'Ag+'in'steps'1'and'2,'we'still'need'to'perform'steps'3'and'4'since'we'introduced'a'new'cation'(Na+)'during'the'separation'process'

94(

Qualita;ve,Analysis,•  If(an(analysis(is(needed(for(any(of(the(alkali(metal(ions,(precipitation(is(not(going(to(work((why?)(

(•  To(analyse(for(alkali'metal'ions'or'alkaline'earth'metal'ions,(we(perform(a(_lame'test'•  Metal(ions(emit(speci?ic(colours(when(its(solution(is(introduced(to(a(hot(?lame(

95(

↳ They will never form PPT to visibly show theyare present

Qualita;ve,Analysis,•  Here(are(a(few(ions(and(their(colours:((

96(

Ej:

O

97(

0

Qualita;ve,Analysis,

98(

-lavender→ yellow orange✓magenta

RED ← -mint

#pickle to live

Qualita;ve,Analysis,•  First,(remove'all'other'ions'by'precipitation'to(minimize(interference(•  Dip(a(platinum(or(nichrome(wire((wooden(splints(or(cotton(swab(will(work(too(if(on(a(tight(budget…!)(into(the(solution(or(salt(precipitate(and(place(it(over(a(hot((blue)(?lame(•  Observe(the(colour(and(match(to(one(of(the(known(?lame(colours(

100(

Qualita;ve,Analysis,•  Provide(a(procedure(that(allows(you(to(analyze(the(presence(of(the(following(cations(in(solution:(Cu2+,(Pb2+,(Mg2+,(K+(

(((((

•  By(looking(at(the(solubility(table,(we(see:(! Cl@,(Br@,(I@,(and(SO42@(will(precipitate(only(Pb2+(! S2@(will(precipitate(only(Pb2+(and(Cu2+(! OH@,(PO43@,(SO32@,(CO32@(will(precipitate(all(but(K+(! Nothing(will(precipitate(K+ (((

101(

Cu2+(Pb2+(Mg2+(K2+(

HzS04 H2S NH4OH

CT,ITBr-

5042- S2- OH

- 1204705,5032-

no PPT - PPT PPT PPT

PPT PPT PPT PPT PPT-- - PPT PPT

a-

-

- - -

I, Add H2S 04 . If PPT forms, Pbs046)will confirm presence of pbzt.Filter PPT. Keep filtrate .

2. Add H2S to filtrate .

If PPT forms

CUS Cs) will confirm presence ofcat

Fitter PPT. Keep filtrate .

3, Add NH4OH to form PPT Mgcotttcs)

.

Fitter PPT . Keep filtrate .

4. Flame test for the presence of KT.

If Violet flame shows, it confirms

presence of Kt.

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