Qualitative Analysis - [scale=.5]kvali2anlcd.elte.hu/szalai/pdf/qualitative_analysis4.pdf · Cations (Group I-III) The cations of Group I can be precipitated as sul des from acidic

Qualitative Analysis

Istvan Szalai

Institute of Chemistry, Eotvos University

2016

Istvan Szalai Qualitative Analysis

Cations (Group I-III)

The cations of Group I can be precipitated as sulfides from acidicsolution (pH∼2) by H2S; the precipitates are insoluble in (NH4)2Sand KOH.

The cations of Group II can be precipitated in acidic media withH2S but the sulfides of are soluble in (NH4)2Sx and KOH withformation of thiocomplexes.

The cations of Group III can be precipitated with (NH4)2S inneutral or slightly alkaline solutions, but cannot be precipitatedwith H2S in acidic solutions.



Hydrolysis (pH=5):Bi(OH)3, Sb(OH)3, SbO(OH)3, Sn(OH)2, Sn(OH)4, Al(OH)3,Cr(OH)3, Fe(OH)3

HCl:AgCl, Hg2Cl2, PbCl2



Hydrolysis (pH=5):Bi(OH)3, Sb(OH)3, SbO(OH)3, Sn(OH)2, Sn(OH)4, Al(OH)3,Cr(OH)3, Fe(OH)3

HCl:AgCl, Hg2Cl2, PbCl2



NaOH (2M):White precipitates:Bi(OH)3, Pb(OH)2, Cd(OH)2, Sn(OH)2, Sn(OH)4, Sb(OH)3,SbO(OH)3, Al(OH)3, Zn(OH)2

Soluble in excess of NaOH:Pb(OH)2−4 , Sn(OH)2−4 , Sn(OH)2−6 , Sb(OH)−4 , Sb(OH)−6 ,Zn(OH)2−4 , Al(OH)−4



NaOH (2M):White precipitates:Bi(OH)3, Pb(OH)2, Cd(OH)2, Sn(OH)2, Sn(OH)4, Sb(OH)3,SbO(OH)3, Al(OH)3, Zn(OH)2Soluble in excess of NaOH:Pb(OH)2−4 , Sn(OH)2−4 , Sn(OH)2−6 , Sb(OH)−4 , Sb(OH)−6 ,Zn(OH)2−4 , Al(OH)−4



NaOH (2M):Colored precipitates:Ag2O, HgO, Cu(OH)2, Ni(OH)2, Co(OH)2, Mn(OH)2, Fe(OH)2,Fe(OH)3, Cr(OH)3

Soluble in excess:Cr(OH)−4

Can be reduced by H2O2 in basic solution:Ag2O, HgOCan be oxidized by H2O2 in basic solution:Co(OH)2, Cr(OH)3, Mn(OH)2, Fe(OH)2



NaOH (2M):Colored precipitates:Ag2O, HgO, Cu(OH)2, Ni(OH)2, Co(OH)2, Mn(OH)2, Fe(OH)2,Fe(OH)3, Cr(OH)3Soluble in excess:Cr(OH)−4




NaOH (2M):Colored precipitates:Ag2O, HgO, Cu(OH)2, Ni(OH)2, Co(OH)2, Mn(OH)2, Fe(OH)2,Fe(OH)3, Cr(OH)3Soluble in excess:Cr(OH)−4




NH3 (2M):The first reaction is the same like with NaOH (except Hg(I) andHg(II)).

Complex formation in excess of NH3:Ag(NH3)+2 , Cd(NH3)2+4 , Zn(NH3)2+4 , Cu(NH3)2+4 , Ni(NH3)2+6 ,Co(NH3)2+6



NH3 (2M):The first reaction is the same like with NaOH (except Hg(I) andHg(II)).Complex formation in excess of NH3:Ag(NH3)+2 , Cd(NH3)2+4 , Zn(NH3)2+4 , Cu(NH3)2+4 , Ni(NH3)2+6 ,Co(NH3)2+6



H2S (pH=2):Black or brown precipitates:Bi2S3, PbS, HgS, CuS, Ag2S, SnS

Yellow or orange precipitates:Sb2S3, CdS, SnS2, As2S3

White precipitates (in buffered or basic solution): ZnSRedox reaction: Fe3+, As(V), Sb(V)



H2S (pH=2):Black or brown precipitates:Bi2S3, PbS, HgS, CuS, Ag2S, SnSYellow or orange precipitates:Sb2S3, CdS, SnS2, As2S3




H2S (pH=2):Black or brown precipitates:Bi2S3, PbS, HgS, CuS, Ag2S, SnSYellow or orange precipitates:Sb2S3, CdS, SnS2, As2S3




(NH4)2S:Black or brown precipitates:Bi2S3, PbS, HgS, CuS, Ag2S, NiS, CoS, FeS, Fe(OH)3

Other precipitates:ZnS, CdS, MnS, Cr(OH)3, Al(OH)3Thiocomplexes:AsS3−

3 , AsS3−4 , SbS3−

3 , SbS3−4 , SnS3−

3



(NH4)2S:Black or brown precipitates:Bi2S3, PbS, HgS, CuS, Ag2S, NiS, CoS, FeS, Fe(OH)3Other precipitates:ZnS, CdS, MnS, Cr(OH)3, Al(OH)3

Thiocomplexes:AsS3−

3 , AsS3−4 , SbS3−

3 , SbS3−4 , SnS3−

3



(NH4)2S:Black or brown precipitates:Bi2S3, PbS, HgS, CuS, Ag2S, NiS, CoS, FeS, Fe(OH)3Other precipitates:ZnS, CdS, MnS, Cr(OH)3, Al(OH)3Thiocomplexes:AsS3−

3 , AsS3−4 , SbS3−

3 , SbS3−4 , SnS3−

3



KI:Colored precipitates:BiI3, Hg2I2, HgI2, PbI2, AgI, CuI

Complexes:BiI−4 , HgI2−4 , CdI2−4 , (PbI2−4 ), (AgI−2 ), (CuI−2 )Redox reaction:Cu2+, Fe3+, As(V), Sb(V)

I2 (I−3 ):In acidic solution: Sn(II)After adding NaHCO3: AsO3−

3



KI:Colored precipitates:BiI3, Hg2I2, HgI2, PbI2, AgI, CuIComplexes:BiI−4 , HgI2−4 , CdI2−4 , (PbI2−4 ), (AgI−2 ), (CuI−2 )

Redox reaction:Cu2+, Fe3+, As(V), Sb(V)


3



KI:Colored precipitates:BiI3, Hg2I2, HgI2, PbI2, AgI, CuIComplexes:BiI−4 , HgI2−4 , CdI2−4 , (PbI2−4 ), (AgI−2 ), (CuI−2 )

Redox reaction:Cu2+, Fe3+, As(V), Sb(V)


3



KI:Colored precipitates:BiI3, Hg2I2, HgI2, PbI2, AgI, CuIComplexes:BiI−4 , HgI2−4 , CdI2−4 , (PbI2−4 ), (AgI−2 ), (CuI−2 )Redox reaction:Cu2+, Fe3+, As(V), Sb(V)


3



KI:Colored precipitates:BiI3, Hg2I2, HgI2, PbI2, AgI, CuIComplexes:BiI−4 , HgI2−4 , CdI2−4 , (PbI2−4 ), (AgI−2 ), (CuI−2 )Redox reaction:Cu2+, Fe3+, As(V), Sb(V)


3



KMnO4 (slightly acidic solution):Sn(II), Fe(II), Hg2+2 , Sb(III), As(III)

Zn:Acidic solution:Ag+, Cu2+, Hg2+2 , Hg2+, Bi3+, As(III), As(V), Sb(III), Sb(V),Sn(II), Sn(IV), (Cd2+), (Pb2+), (Ni2+), (Co2+)Fe(III)−→ Fe(II)



KMnO4 (slightly acidic solution):Sn(II), Fe(II), Hg2+2 , Sb(III), As(III)

Zn:Acidic solution:Ag+, Cu2+, Hg2+2 , Hg2+, Bi3+, As(III), As(V), Sb(III), Sb(V),Sn(II), Sn(IV), (Cd2+), (Pb2+), (Ni2+), (Co2+)Fe(III)−→ Fe(II)


Midterm 1

Date: March 17th 2016, 12:15-13:45Tools: pen, calculator (non programmable)The use of mobilephone (iphone) is forbidden!


Solubility of sulfides in acidic solutions

Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

Does the ZnS precipitate form in a solution which is 0.1M foraceteic acid and 0.01M for Zn2+ ions and saturated with H2S?

Ka(CH3COOH) = 2× 10−5, Ka1(H2S) = 1× 10−7

Ka2(H2S) = 1× 10−13, Ksp = 1× 10−21



Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

[H+] =√

[CH3COOH]Ka =√

0.1× 2× 10−5 = 1.41× 10−3M

αH =

(1 +

1.41× 10−3

10−13+

(1.41× 10−3)2

10−1310−7

)= 1.98× 1014

[S2−] =[S2−]tαH

=0.1

1.98× 1014= 5× 10−16



Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

[H+] =√

[CH3COOH]Ka =√

0.1× 2× 10−5 = 1.41× 10−3M

αH =

(1 +

1.41× 10−3

10−13+

(1.41× 10−3)2

10−1310−7

)= 1.98× 1014

[S2−] =[S2−]tαH

=0.1

1.98× 1014= 5× 10−16



Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

[H+] =√

[CH3COOH]Ka =√

0.1× 2× 10−5 = 1.41× 10−3M

αH =

(1 +

1.41× 10−3

10−13+

(1.41× 10−3)2

10−1310−7

)= 1.98× 1014

[S2−] =[S2−]tαH

=0.1

1.98× 1014= 5× 10−16



Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

[S2−] =[S2−]tαH

=0.1

1.98× 1014= 5× 10−16

Q = [Zn2+][S2−] = 10−2 × 5× 10−16 = 5× 10−18

Q = 5× 10−18 > Ksp = 1× 10−21

The precipitation of ZnS occurs at this conditions.



Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

[S2−] =[S2−]tαH

=0.1

1.98× 1014= 5× 10−16

Q = [Zn2+][S2−] = 10−2 × 5× 10−16 = 5× 10−18

Q = 5× 10−18 > Ksp = 1× 10−21




Zn2+ + S2− −−⇀↽−− ZnSS2− + H+ −−⇀↽−− HS−

HS− + H+ −−⇀↽−− H2S

[S2−] =[S2−]tαH

=0.1

1.98× 1014= 5× 10−16

Q = [Zn2+][S2−] = 10−2 × 5× 10−16 = 5× 10−18

Q = 5× 10−18 > Ksp = 1× 10−21



Midterm 1

Which of the following ions give precipitate with ammonium-sulfidein neutral solution?

Yes No

AsO3−3

I−

Cr3+

Cu2+

Hg2+

Yes No

Al3+

SnCl2−4Ag+

Cd2+

SbCl−4Write the reactions:


Midterm 1


Yes No

AsO3−3

I−

Cr3+

Cu2+

Hg2+

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I−

Cr3+

Cu2+

Hg2+

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+

Cu2+

Hg2+

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+

Hg2+

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+ +

SnCl2−4Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+ +

SnCl2−4 +

Ag+

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+ +

SnCl2−4 +

Ag+ +

Cd2+



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+ +

SnCl2−4 +

Ag+ +

Cd2+ +



Midterm 1


Yes No

AsO3−3 +

I− +

Cr3+ +

Cu2+ +

Hg2+ +

Yes No

Al3+ +

SnCl2−4 +

Ag+ +

Cd2+ +

SbCl−4 +Write the reactions:


Midterm 1

Which of the following can not be dissolved in water, but can bedissolved in sodium-hidroxide?

Yes No

Cd(OH)2Al(OH)3

Cr2(SO4)3PbSO4

Ni(OH)2

Yes No

PbS

As2O3

Sb2S3

ZnSO4

AgClWrite the reactions:


Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3Cr2(SO4)3

PbSO4

Ni(OH)2

Yes No

PbS

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3PbSO4

Ni(OH)2

Yes No

PbS

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4

Ni(OH)2

Yes No

PbS

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4

Ni(OH)2

Yes No

PbS

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2

Yes No

PbS

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS +

As2O3

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS +

As2O3 +

Sb2S3

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS +

As2O3 +

Sb2S3 +

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS +

As2O3 +

Sb2S3 +

ZnSO4



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS +

As2O3 +

Sb2S3 +

ZnSO4 +



Midterm 1


Yes No

Cd(OH)2 +

Al(OH)3 +

Cr2(SO4)3 +

PbSO4 +

Ni(OH)2 +

Yes No

PbS +

As2O3 +

Sb2S3 +

ZnSO4 +

AgCl +Write the reactions:


Midterm 1

What single reagent could be used to distinguish between membersof the following pairs?

I CdS, SnS2

I Pb(OH)2−4 , Sn(OH)2−4I Sn(Cl)2−4 , Sb(Cl)−4I Cu(NH3)2+4 , Ni(NH3)2+6


Midterm 1


I CdS, SnS2

NaOH

I Pb(OH)2−4 , Sn(OH)2−4I Sn(Cl)2−4 , Sb(Cl)−4I Cu(NH3)2+4 , Ni(NH3)2+6


Midterm 1


I CdS, SnS2

NaOH

I Pb(OH)2−4 , Sn(OH)2−4Bi(OH)3

I Sn(Cl)2−4 , Sb(Cl)−4I Cu(NH3)2+4 , Ni(NH3)2+6


Midterm 1


I CdS, SnS2

NaOH


I Sn(Cl)2−4 , Sb(Cl)−4Hg2+

I Cu(NH3)2+4 , Ni(NH3)2+6


Midterm 1


I CdS, SnS2

NaOH


I Sn(Cl)2−4 , Sb(Cl)−4Hg2+

I Cu(NH3)2+4 , Ni(NH3)2+6Fe


Midterm 1

How can you identify

I Cd2+ Cu2+ in presence of

I Zn2+ Pb2+ in presence of

I Ca2+ Ba2+ in presence of


Midterm 1


I Cd2+ Cu2+ in presence ofNH3, KCN,H2S

I Zn2+ Pb2+ in presence of



Midterm 1



I Zn2+ Pb2+ in presence ofNH3, (NH4)2S



Midterm 1



I Zn2+ Pb2+ in presence ofNH3, (NH4)2S

I Ca2+ Ba2+ in presence of(NH4)2(COO)2


Midterm 1

How can you identify Co(II), Cu(II) and Fe(III) ions in presence ofeach other?


Midterm 1

How can you identify Co(II), Cu(II) and Fe(III) ions in presence ofeach other?

I Fe

I NH4SCN, NaF


Midterm 1

Which of the substance can be identified by following the nextdescription?

1. White crystalline compound, that dissolves in water. Thesolution is colorless and acidic.

2. White precipitate forms with ammonia, which can not bedissolved in excess of ammonia.

3. White precipitate forms with sodium-hidroxide, which can bedissolved in excess of sodium-hidroxide. Boiling the alkalinesolution no change and no specific odour can be obderved.

4. White precipitate forms with perchloric acid from the originalsolution.

5. White precipitate forms with barium-chloride, which can notbe dissolved in 20% HCl.


Midterm 1

1. White crystalline compound, that dissolves in water. Thesolution is colorless and acidic.Excluded ions: Cu(II), Co(II), Ni(II), Cr(III), Fe(II), Fe(III),Mn(II)

2. White precipitate forms with ammonia, which can not bedissolved in excess of ammonia.One of these ions must be: Hg(I), Hg(II), Pb(II), Bi(III),Sn(II), Sn(IV), Al(III), Mg2+

No informations about: Ag+, Cd2+, As(III), As(V), Ca2+,Ba2+, Na+, K+, NH +

4


Midterm 1

1. White crystalline compound, that dissolves in water. Thesolution is colorless and acidic.Excluded ions: Cu(II), Co(II), Ni(II), Cr(III), Fe(II), Fe(III),Mn(II)

2. White precipitate forms with ammonia, which can not bedissolved in excess of ammonia.One of these ions must be: Hg(I), Hg(II), Pb(II), Bi(III),Sn(II), Sn(IV), Al(III), Mg2+

No informations about: Ag+, Cd2+, As(III), As(V), Ca2+,Ba2+, Na+, K+, NH +

4


Midterm 1

3. White precipitate forms with sodium-hidroxide, which can bedissolved in excess of sodium-hidroxide. Boiling the alkalinesolution no change and no specific odour can be obderved.Excluded ions: Ag+, Cd2+, Hg(I), Hg(II), Bi(III),Mg2+, NH +

4

Possible ions: Pb2+ vagy Al3+

No infos: As(III), As(V), Ca2+, Ba2+, Na+, K+


Midterm 1

4. White precipitate forms with perchloric acid from the originalsolution.K+

5. White precipitate forms with barium-chloride, which can notbe dissolved in 20% HCl.SO 2–

4 !, excluded ions Pb2+, Ca2+, Ba2+

Possible ion Al3+, and no infos about As(III), As(V), Na+.

Substance:KAl(SO4)2


Midterm 1

4. White precipitate forms with perchloric acid from the originalsolution.K+

5. White precipitate forms with barium-chloride, which can notbe dissolved in 20% HCl.SO 2–

4 !, excluded ions Pb2+, Ca2+, Ba2+

Possible ion Al3+, and no infos about As(III), As(V), Na+.

Substance:KAl(SO4)2


Midterm 1

How many iron(II)-chloride can be dissolved in a mixture of 50cm3 0.1 mol/dm3 acetic acid and 50 cm3 0.1 mol/dm3

sodium-hidroxide?MM(iron(II)-chloride)=127 g/mol, Ksp = 1× 10−14

Ks(acetic acid) = 2× 10−5


Midterm 1

How many gramms of sodium-hydroxide (MM=40) is dissolved in100 cm3 of 0.25 mol/dm3 acetic acid if the pH is 5.0? What is thesolubility of the ZnS in this solution after saturating with H2S(cH2S = 0.1 mol/dm3)?Ksp = 1× 10−21

Ka(acetic acid)= 2× 10−5

Ka1(H2S)= 10−7

Ka2(H2S)= 10−13


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Qualitative Analysis - [scale=.5]kvali2anlcd.elte.hu/szalai/pdf/qualitative_analysis4.pdf · Cations (Group I-III) The cations of Group I can be precipitated as sul des from acidic