SCH4C                                                Qualitative Analysis
Reactions
The reactions given below are correct to the best of my understanding of the subject material.  If there are any corrections please contact me.
Rxn Set #1 
 
 
 

 

These are the reaction that produce the Group 1 precipitates.
 
Ag+1(aq)  +  Cl-1(aq)  ---------->  AgCl(white ppt)
Pb+2(aq)  +  2 Cl-1(aq)  ---------->  PbCl2 (white ppt)
Hg2+2(aq)  +  Cl-1(aq)  ---------->  Hg2Cl2  (white ppt)
Rxn Set #2
 
 
 

 

These are the reactions that produce the Group 2 precipitates.
Hg2+(aq)  +   S2-(aq) ------->  HgS (black ppt)
Pb2+(aq)  +   S2-(aq) ------->  PbS (black ppt)
2 Bi3+(aq)  +  3 S2-(aq) ------->  Bi2S3 (brown ppt)
Cu2+(aq)  +   S2-(aq) ------->  CuS (dark brown ppt)
Cd2+(aq)  +   S2- (aq) ------->  CdS (yellow ppt)
Sn4+(aq)  +   2 S2-(aq) ------->  SnS2 (yellow ppt)
Rxn Set #3
 
 
 

 

These are the reactions that produce the Group 3 precipitates.
NH3(g)  +  H2O(l) ----->  NH4OH(aq)  ----->  NH41+(aq)  +  OH1-(aq)
2 NH4OH(aq)  +  H2S(g) ----->    NH41+(aq)  +  S2-(aq)  +  2 H2O
Al3+(aq)  +  3 OH-1(aq) ----->  Al(OH)3 (white flocculent ppt)
Cr3+(aq)  +  3 OH-1(aq) ----->  Cr(OH)3 (green flocculent ppt)
Fe2+(aq)  +   S2-(aq) ------->  FeS (brown ppt)
2 Fe3+(aq)  +   3 S2-(aq) ------->  Fe2S3 (brown ppt)
Mn2+(aq)  +   S2-(aq) ------->  MnS (flesh coloured ppt)
Zn2+(aq)  +   S2-(aq) ------->  ZnS (white ppt)
Ni2+(aq)  +   S2-(aq) ------->  NiS (black ppt)
Co2+(aq)  +   S2-(aq) ------->  CoS (black ppt)
Rxn Set #4 
 
 
 

 

 These are the reactions that produce the Group 4 precipitates.
Ba2+(aq)   +   CO32-(aq)   ----->  BaCO3 (white ppt)
Ca2+(aq)   +   CO32-(aq)   ----->  CaCO3 (white ppt)
Sr2+(aq)   +   CO32-(aq)   ----->  SrCO3 (white ppt)
Mg2+(aq)   +   CO32-(aq)   ----->  MgCO3 (white ppt)
Rxn #5  Pb2+(aq) + CrO42-(aq)  ------>  PbCrO4 (yellow ppt)
Rxn  #6  AgCl(s) +  2 NH4OH(aq) -----> Ag(NH3)21+(aq)   +   H2O(l)   +  Cl1-(aq)
Rxn #7  Ag(NH3)21+(aq)   +  2 H1+(aq)  + Cl1- ----->  AgCl (white ppt)  +  2 NH4OH(aq)
Rxn  #8 
reaction (i)     Hg2Cl2  -->  Hg2+ (aq)  +  Hgo(black ppt)  +  2 Cl1-(aq)
reaction (ii)    NH3 (aq)   +  NH3 (aq)   ----->   NH41+(aq)  +  NH21-(aq)
reaction (iii)   Hg2+ (aq)  + NH21-(aq)  +  Cl1-(aq)  ---->  Hg(NH2)Cl  (white ppt)
_____________________________________________________________
overall rxn    Hg2Cl2 + 2 NH3(aq)  ----->   Hgo + Hg(NH2)Cl +  NH41+(aq)  +  Cl1- (aq)
Rxn  #9 
Dissolving the Group 2 cations in dilute HNO3.
HgS  + HNO3  ----> no reaction
3 PbS(s)  +  8 H1+(aq)  + 2 NO31-(aq)  ---->  3 So(s)  +  2 NO(g)  +  4 H2O(l)  +  3 Pb2+(aq)
3 CuS(s)  +  8 H1+(aq)  + 2 NO31-(aq)  ---->  3 So(s)  +  2 NO(g)  +  4 H2O(l)  +  3 Cu2+(aq)
3 Bi2S3(s)  +  8 H1+(aq)  + 2 NO31-(aq)  ---->  3 So(s)  +  2 NO(g)  +  4 H2O(l)  +  2 Bi3+(aq)
3 CdS(s)  +  8 H1+(aq)  + 2 NO31-(aq)  ---->  3 So(s)  +  2 NO(g)  +  4 H2O(l)  +  3 Cd2+(aq)
Rxn  #10
Dissolution of HgS in "aqua regia"
3 HgS(s)  +  2 NO31-(aq)  + 12 Cl1-(aq)  + 8 H1+(aq)  -->  3 HgCl42-(aq)  + 2 So  + 2 NO(g)  + 4 H2O(l)
Reduction of HgCl42- with SnCl2
2 HgCl42-(aq)  +  SnCl2 (aq)  --->  Hg2Cl2 (white ppt)  +  SnCl4 (black ppt)  +  4 Cl1-(aq)
Add SnCl2 in excess and the reaction is:
Hg2Cl2 (white ppt)  +  SnCl2 (aq)  ---->   2 Hgo  +  SnCl4 (black ppt)
Rxn  #11
                                   OH1-
Bi3+ (aq)  +  S2-(aq)  <=======>  BiS(ppt)
                                  OH1-
Pb3+ (aq)  +  S2-(aq)  <=======>  PbS(ppt)
Cd2+ (aq) +  NH3 (aq)  ------->  Cd(NH3)42+ (soluble)
Cu2+ (aq) +  NH3 (aq)  ------->  Cu(NH3)42+ (soluble)
 
Rxn  #12
Bi2S3 (s)  +  6 OH1-(aq)  -----> 2 Bi(OH)3 (ppt)  +  6 S2- (aq)
PbS (s)  +  2 OH1- (aq)  ----->  Pb(OH)2 (ppt)  +   S2-(aq)
Rxn  #13a
Preparation of the sodium stannite reagent
2 NaOH (aq)  +  SnCl2 (aq)  ---->   Na2SnO2 (aq)  +  2 Cl1- (aq)
                                                 sodium stannite
Rxn  #13b 2 Bi(OH)3 (ppt)  +  3 Na2SnO2 (aq)  -------->  2 Bio (s)  + Na2SnO3 (aq)   +   H2O(l)
Rxn  #14 Pb2+ (aq)  +   CrO42-(aq) ---> PbCrO4 (yellow ppt)
Rxn #15 Cu(NH3)42+(aq)  + Cd(NH3)42+(aq)  + 4 Cl1-(aq)  --->  CdCl42-(aq)  + 4 NH3(aq)  + Cu(NH3)42+(aq)
Rxn  #16
                    OH1-
CdCl42-(aq)  ------->  Cd2+(aq)  +  4 Cl1-(aq)
Cd2+(aq)   +   H2S(g)  ------>   CdS (yellow ppt)  + 2 H1+(aq)
 
Rxn  #17
                            SO42- / HSO41- buffer
Al(OH)3 (ppt)   <==================>  Al3+(aq)  +  3 OH1-(aq)
                            SO42- / HSO41- buffer
Cr(OH)3 (ppt)   <==================>  Cr3+(aq)  +  3 OH1-(aq)
                             SO42- / HSO41- buffer
FeS (ppt)   <==================>  2 Fe2+(aq)  +  S2-(aq)
                            SO42- / HSO41- buffer
Fe2S3 (ppt)   <==================>  2 Fe3+(aq)  +  3 S2-(aq)
                            SO42- / HSO41- buffer
MnS (ppt)   <==================>   Mn2+(aq)  +  S2-(aq)
                             SO42- / HSO41- buffer
ZnS (ppt)   <==================>  no reaction
                            SO42- / HSO41- buffer
CoS (ppt)   <==================>   no reaction
                             SO42- / HSO41- buffer
NiS (ppt)   <==================>   no reaction
 
Rxn #18a
                H1+
ZnS (ppt)  ------>  Zn2+(aq)  +  S2-(aq)
                  H1+
CoS (ppt)  ------>    no reaction
                  H1+
NiS (ppt)  ------>    no reaction
 
Rxn #18b
                HCl/NaOCl
NiS (ppt) --------------->  Ni2+(aq)  +  SO2(g)
               HCl/NaOCl
CoS (ppt) --------------->  Co2+(aq)  +  SO2(g)
 
Rxn  #19                                                 NH4OH
Ni2+(aq)   +    (CH3CNOH)2  -------------> red precipitate
                    dimethylgloxime
Rxn  #20                        OH1-
Zn2+ (aq) ----------------> ZnS (white or grey precipitate)
                       H2S
Rxn  #21
                    OH1-
Fe2+ (aq)  --------->   Fe(OH)2 (ppt)
                  OH1-
Fe3+ (aq)  --------->   Fe(OH)3 (ppt)
                   H2O2/OH1-
Mn2+ (aq)  ----------------->   MnO2 (ppt)
                 OH1-
Al3+ (aq)  --------->   Al(OH)3 (ppt)
                  H2O2
Cr3+ (aq)  --------->   CrO42- (aq)
 
Rxn  #22
Fe2+(aq)  +  K3Fe(CN)6(aq)  ----->  Fe4[Fe(CN)6]3.16H2O (prussian blue precipitate)
May confirm Fe2+ if Fe3+ is negative, since Fe3+ also does the same reaction
Fe3+(aq)  +  K3Fe(CN)6(aq)  ----->  Fe4[Fe(CN)6]3.16H2O (prussian blue precipitate)
Rxn  #23                                             H1+
Fe3+(aq)    +    SCN1-(aq)  ------->  FeSCN2+ (aq)  (dark red coloured solution)
Rxn  #24 4 BiO31- (aq)  + 3 Mn2+(aq) ---------->  3 MnO41-(aq)  +  4 Bi5+(aq) 
                                                         (purple colour)
Rxn  #25                     H1+                       OH1-
Al(OH)3  -------->  Al3+ (aq)  --------->  Al(OH)3  (white flocculent precipitate)
                           H1+
CrO42-(aq)  ----------> no reaction
Rxn  #26                     H1+                           OH1-
Al(OH)3  -------->  Al3+ (aq)  -------------------->  Al(OH)3  (red-dyed  precipitate)
                                             (aluminon reagent)
Rxn  #27                                             H1+
CrO42-(aq)   +   Pb2+(aq)  -------->  PbCrO4 (yellow precipitate)
Rxn  #28
                       (HCH3COOH/CH3COO1- buffer)
CaCO3 (ppt) <============================> Ca2+(aq)  +  2 HCO31-(aq)
                       (HCH3COOH/CH3COO1- buffer)
BaCO3 (ppt) <============================> Ba2+(aq)  +  2 HCO31-(aq)
                       (HCH3COOH/CH3COO1- buffer)
SrCO3 (ppt) <============================> Sr2+(aq)  +  2 HCO31-(aq)
 
Rxn  #29a Ba2+(aq)  +  CrO42-(aq) -------->  BaCrO4 (yellow precipitate)
Rxn  #29b                             H1+/OH1-
BaCrO4 (ppt)  <==========>  Ba2+ (aq)  +  CrO42- (aq)

Ba2+ (aq)  +  SO42- (aq)     -------->  BaSO4 (white precipitate)

Rxn  #30 Sr2+ (aq)   +  SO42-(aq)    -------->  SrSO4 (white precipitate)
Rxn  #31 Ca2+ (aq)  +  C2O42-(aq)  ------->  CaC2O4 (white precipitate)
Rxn  #32 Mg2+(aq)  +  H2PO41-(aq) + NH41+(aq) + 2 OH1-(aq) ----> MgNH3PO4 (white ppt) + 2 H2O(l)
Rxn  #33 Mg(CH3COO)2.UO2(CH3COO)2(aq) +  2 Na1+(aq) ----->
                                          Mg2+(aq)  +  Na2(CH3COO)2.UO2(CH3COO)2(ppt)
                                                                  (very pale yellow crystals)
Rxn  #34 2 K1+(aq) + Na2Co(NO2)6(aq)  ----->  K2NaCo(NO2)6 (ppt) + 2 Na1+(aq)
                                                          (yellowish-brown)


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Copyright 1997, 2002, 2003  Tom Stretton (stretton@ripnet.com) Updated August, 2002 ts.