1. GROUP II CATIONS
As+3, As+5, Sb+3, Sb+5, Sn+2,
Cu+2, Cd+2, Bi+3
, Hg+2, Pb+2

2. As+3, As+5, Sb+3, Sb+5, Sn+2, Cu+2, Cd+2, Bi+3
GROUP II CATIONS
As+3, As+5, Sb+3, Sb+5, Sn+2, Cu+2, Cd+2, Bi+3
The specific reactions of Group II cations when they are alone =
The experiments you will perform with known samples of group II cations.

3. Cu+2 1- The solutions of Cu salts have blue or bluish-green color.
You can predict the presence of Cu in your sample just by
looking at the color of your sample.
2- Reaction with K4[Fe(CN)6] (potassium ferrocyanide) :
Red-brown precipitates are formed and they are soluble in diluted ammonia
2Cu+2 + [Fe(CN)6] –4 → Cu2[Fe(CN)6] ↓
3- Reaction with KCN (potassium cyanide):
Firstly greenish-yellow Cu(CN)2 ↓ precipitates are formed and upon excess adition of KCN, it will be dissolved by formation of K3[Cu(CN)4] (potassium cyanocuprate)

4. Cd+2
1- Reaction with H2S: colloidal and yellow colored CdS is formed and it is soluble in HNO3.
Cd+2 +H2S → CdS ↓ (yellow) + 2H+
3CdS + 8H+ + 2NO3– → 3Cd+2 + 3S + 2NO + 4H2O
2- Reaction with KCN: In the beginning, white colored Cd(CN)2 precipitates are formed and upon addition of excess KCN it is dissolved by formation of K2[Cd(CN)4] (potassium tetracyanocadmate(II)) complex. This complex can react with H2S to produce CdS
CdSO4 + 2 KCN → Cd(CN) K2 SO4
Cd(CN)2 + 2 KCN → K2[Cd(CN)4]
K2[Cd(CN)4] + H2S → CdS ↓ + 2KCN +2HCN
Yellow
The last reaction is the difference between Cd+2 and Cu+2 , K3[Cu(CN)4] complex does not react with H2S while K2[Cd(CN)4] reacts.

5. Bi+3
** Main oxidation states of bismuth are +3, –3, +5.
Bi-3 behaves strong reducing agent while Bi+5 is strong oxidizing agent.
1- Reaction with Na2SnO2 (Sodium stannite ):
Bismuth is reduced to black colored metallic Bi0
2Bi(OH) Na2SnO2 → 2Bi0↓+ 3Na2SnO3 + 3H2O
black
2- Reaction with KI:
Bi+3 + KI→ BiI3 ↓ black precipitate
BiI3 + KI ↔ [BiI4]– Soluble complex

6. Sn+2 (Tin)
The hydrolysis of Sn+2 salts produce white precipitates of Sn(OH)Cl.
1- Reaction with H2S: Brown SnS precipitates.
Brown precipitate might turn to black later
2- Tin reduce Bi+3 to black Bi0 in basic medium. Add NaBiO3 (sodium bismuthate) prepared in basic medium.

7. Sn+2 (Tin) 3- Luminescence test:
The sample is directly used without any pretreatment.
Fill a test tube with cold tap water.
Put 5 mL sample into a small beaker.
Add 3 mL HCl into the beaker.
Add Zn granules (2 microspatula) into the beaker.
Immerse the test tube into the beaker.
Hold the bottom of the test tube directly into the reducing zone of the flame)
Blue shining (luminescence) indicates the presence of Sn+2
Luminescence is seen outside of the test tube.

8. As+3, As+5 (Arsenic)
They both form strong covalent bonds with oxygen in water
As+3 : AsO3–3, AsO2– (arsenite)
As+5 : AsO4– (arsenate)
1-Reaction with AgNO3 yields yellow colored Ag3AsO4 (silver arsenate).
3Ag+ + AsO4- → Ag3AsO4↓
yellow

9. It can produce white colored SbOCl precipitates in water.
Sb+3, Sb+5 (Antimony)
It can produce white colored SbOCl precipitates in water.
1- Reaction with H2S: Orange Sb2S3 (antimony sulfide) precipitates
2Sb H2S → Sb2S3 ↓ + 6H+
orange ... brown
2- Reaction with NaOH: White colored SbOCl precipitates.
SbCl3 + NaOH → SbOCl ↓ + HCl + NaCl
white

10. Pb2+ (Lead) Hg+2 (Mercury) Copper strip (Amalgam test):
Reaction with potassium chromate (K2CrO4): yellow lead chromate precipitates
Pb2+ + K2CrO4 → PbCrO4↓(s) + 2K+
yellow precipitates
Hg+2 (Mercury)
Copper strip (Amalgam test):
A piece of copper wire is cleaned with 8-10 drops of concentrated HNO3 solution in the watch glass, then it is dried by filter paper and mercury sample solution is added to the copper strip. Mercury ions reduce and coat the copper strip (bright gray colored).

12. Ksp values of Group II and Group III cations
In systematic analysis of cations, 13 cations are precipitated as their sulfides. Among these cations, 8 of them have lower solubilities in water and they are called as Group II cations while the remaning 5 cations with higher solubility in water are called as Group III cations:
Ksp values of Group II and Group III cations
Group II
Group III
Sulfides
Ksp
HgS
3,0x10–53
ZnS
1,2x10–23
CuS
1,0x10–44
CoS
7,0x10–23
Bi2S3
1,6x10–72
NiS
1,4x10–24
Sb2S3
1x10–30
FeS
3,7x10–19
CdS
3,6x10–29
MnS
1,4x10–15
PbS
3,4x10–28
SnS
1,8x10–28
As2S3
4,4x10–27
When a sulfide reactant is added, in a medium of 0.3 M acid, Group II cations with lower solubility precipitate while Group III cations having higher solubility remain in the solution. For this reason, adjustment of acidity is important in separation of these two groups.

13. The equilibrium for hydrogen sulfide:
H2S ↔ 2 H+ + S–2
k= [H + ] 2 [ S −2 ] [ H 2 S] = 6,8 x 10–23
In this equilibrium, [H+] = 0.3 M since the acidity of the medium is adjusted to 0.3 M and [H2S]=0.1 M since the highest concentration of it is 0.1 M at 25oC considering the solubility:
0,3 2 [ S −2 ] 0,1 = 6,8 x 10–23
[S–2] = 7,5 x 10–23
Among Group III cations, NiS has the lowest solubility and in our courses the samples are prepared in M:
Q= [Ni+2] [S–2] = 0,01 x 7,5 x 10–23 = 7,5 x 10–25
7,5 x 10–25 < Ksp (1,4x10-24)
Since Q is smaller than Ksp NiS does not precipitate. The other Group III cations have higher Ksp than NiS and all of them stay dissolved.
On the other hand Q of Group II cations are higher than Ksp of them in this medium and it means all Group II cations will be precipitated.

14. Thioacetamide can be used as sulfide source
Thioacetamide can be used as sulfide source. Hydrogen sulfide will be produced when thioacetamide solution is heated. For this reason, the test tube containing your sample will be heated in a water bath after addition of required amount of thioacetamide. Since the produced hydrogen sulfide will immediately react with cations in the sample, hazardous effects of hydrogen sulfide such as rotten egg smell will be reduced.
In the analysis, the flow chart will be followed.
Sulfides of Group II cations have different colors so you may have preliminary information at the beginning of the analysis:
Bi2S3,HgS, CuS, PbS = Black
As2S3, As2S5 = Yellow
CdS = Pale yellow
Sb2S3, Sb2S5 = Orange / red / brown
SnS = Brown

15. GROUP II CATIONS SUPERNATANT A: AsO3-3, AsS3-3, SbO2-, SbS2-, SnO2-2
Dissolve in 16 drops of aqua regia.
Dry it up in a cruicible
Dissolve it in 2-3 mL distilled water and pour it onto a cupper wire. Hg test is positive if the cupper is covered with gray colored Hg.
PRECIPITATE B: HgS
Wash precipitate
Add 20 drops of NH4CH3COO, 6 drops of 6 M CH3COOH and 4 drops of 1M K2CrO4. Pb test is positive if yellow precipitates are formed.
PRECIPITATE D: Bi(OH)3
Add 10 drops of Na2SnO2. Bi test is positive if the color of precipitate turns to black.
PRECIPITATE A: HgS, CuS, CdS, PbS, Bi2S3
GROUP II CATIONS
40 drops of sample
4 drops of concentrated HCl
14 drops of thioacetamide (11%, w/v) and heat in water bath (5 min)
Centrifuge (3000 rpm, 4 min) decant the liquid part
Wash the precipitate with the washing solution
(washing solution: 2 drops of NH4Cl, 2 drops of thioacetamide and 16 drops of distilled water)
HgS, CuS, CdS, PbS, Bi2S3 As2S3, SnS, Sb2S3
20 drops of 3 M KOH
Heat in water bath for 3 min
Wash with 10 drops of 3M KOH and wash with 20 drops of distilled water
24 drops of 6 M HNO3
Heating in a water bath for 5 min
SUPERNATANT B: Pb2+, Bi+3, Cu+2, Cd+2
2 drop of 6 M H2SO4
Evaporate the solvent in a crucible.
Cool it until room temperature
Add 40 drops of distilled water and stir.
PRECIPITATE C: PbSO4
SUPERNATANT C: Bi+3, Cu+2, Cd+2
Add NH4OH until the solution is basic and then add excess 3 drops of NH4OH
SUPERNATANT D: Cu+2, Cd+2
Add drop by drop 1 M KCN until blue color disappears.
Add excess (2-3 drops) KCN
Add 6 drops of thioacetamide (11% w/v)
Heat it in a water bath for 5 min. Cd test is positive if yellowish precipiates are formed.
Cu test is positive if the supernatant C is blue.
If supernatant C is blue
If supernatant C is not blue
Heat in a water bath for 5 min. Cd test is positive if yellowish precipiates are formed.
Add 3 M HCl until the supernatant is mild acidic. Precipitates will be fomed if at least one of the analyte exist in the sample.
Discard the supernatant and keep the precipitate.
Add 20 drops of concentrated HCl.
Heat in a water bath for 5 min.
PRECIPITATE E: As2S3 ve As2S5
Wash with 10 drops of distilled water for three times.
Add 20 drops of concentrated HNO3.
Heat and stir in a water bath for 5 min
Add 10 drops of 0.5 M AgNO3 and stir.
Add 10 drops of 2.5 M sodium acetate. As3+ is positive if red-brown colored Ag3AsO4 precipitates are formed.
SUPERNATANT E: Sn+4 ve Sb+3
Divide into two parts
Add drop by drop NaOH until the solution is basic.
Add few drops of Sodium bismuthate solution. Sn+4 test is positive if black precipitates are formed after a while.
Sn+4 test
Sb+3 test
Add 6 drops of thioacetamide and heat in a water bath. Sb+3 test is positive if orange colored Sb2S3 precipitates are formed.

16. GROUP II CATIONS SUPERNATANT A: AsO3-3, AsS3-3, SbO2-, SbS2-, SnO2-2
Dissolve in 16 drops of aqua regia.
Dry it up in a cruicible
Dissolve it in 2-3 mL distilled water and pour it onto a cupper wire. Hg test is positive if the cupper is covered with gray colored Hg.
PRECIPITATE B: HgS
Wash precipitate
Add 20 drops of NH4CH3COO, 6 drops of 6 M CH3COOH and 4 drops of 1M K2CrO4. Pb test is positive if yellow precipitates are formed.
PRECIPITATE D: Bi(OH)3
Add 10 drops of Na2SnO2. Bi test is positive if the color of precipitate turns to black.
PRECIPITATE A: HgS, CuS, CdS, PbS, Bi2S3
GROUP II CATIONS
40 drops of sample
4 drops of concentrated HCl
14 drops of thioacetamide (11%, w/v) and centrifuge (3000 rpm, 4 dk)
After heating in water bath for 5 min, decant the liquid part and wash precipitate with the washing solution
(washing solution: 2 drops of NH4Cl, 2 drops of thioacetamide and 16 drops of distilled water)
HgS, CuS, CdS, PbS, Bi2S3 As2S3, SnS, Sb2S3
20 drops of 3 M KOH
Heating in water bath for 3 min
Wash with 10 drops of 3M KOH and wash with 20 drops of distilled water
24 drops of 6 M HNO3
Heating in a water bath for 5 min
SUPERNATANT B: Pb2+, Bi+3, Cu+2, Cd+2
2 drop of 6 M H2SO4
Evaporate the solvent in a crucible.
Cool it until room temperature
Add 40 drops of distilled water and stir.
PRECIPITATE C: PbSO4
SUPERNATANT C: Bi+3, Cu+2, Cd+2
Add NH4OH until the solution is basic and then add excess 3 drops of NH4OH
SUPERNATANT D: Cu+2, Cd+2
Add drop by drop 1 M KCN until blue color disappears.
Add excess (2-3 drops) KCN
Add 6 drops of thioacetamide (11% w/v)
Heat it in a water bath for 5 min. Cd test is positive if yellowish precipiates are formed.
Cu test is positive if the supernatant C is blue.
If supernatant C is blue
If supernatant C is not blue
Heat in a water bath for 5 min. Cd test is positive if yellowish precipiates are formed.
Add 3 M HCl until the supernatant is mild acidic. Precipitates will be fomed if at least one of the analyte exist in the sample.
Discard the supernatant and keep the precipitate.
Add 20 drops of concentrated HCl.
Heat in a water bath for 5 min.
PRECIPITATE E: As2S3 ve As2S5
Wash with 10 drops of distilled water for three times.
Add 20 drops of concentrated HNO3.
Heat and stir in a water bath for 5 min
Add 10 drops of 0.5 M AgNO3 and stir.
Add 10 drops of 2.5 M sodium acetate. As3+ is positive if red-brown colored Ag3AsO4 precipitates are formed.
SUPERNATANT E: Sn+4 ve Sb+3
Divide into two parts
Add drop by drop NaOH until the solution is basic.
Add few drops of Sodium bismuthate solution. Sn+4 test is positive if black precipitates are formed after a while.
Sn+4 test
Sb+3 test
Add 6 drops of thioacetamide and heat in a water bath. Sb+3 test is positive if orange colored Sb2S3 precipitates are formed.

17. ATTENTION!!!
*While working with KCN (For Cu+2 and Cd+2 tests), the medium must be strictly checked with litmus paper for its basicity. If the solution is acidic, then highly toxic HCN gas is evolved.
KCN + H+ → HCN (g)