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cations gp II

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cations gp II

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cations gp II

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  1. Gp ii cations Identification

  2. ilos • Properties of gp II cations • Use different properties for separation and identification of its members

  3. Hg2+ Bi3+ Cu2+ Cd2+ Pb2+ Soluble chloride salts Pb2+ Sb3+, Sb5+ Sn2+, Sn4+ Soluble chloride complex ions: Soluble acids: HAsO2, H2AsO4- • As3+, As5+

  4. Remember gpIPb2+, Hg+ ?

  5. Solubility & Order of separation All their sulfides are soluble in dilute HCl All their sulfides are insoluble in dilute HCl S2- /dilHCl

  6. Solubility & Order of separation Acidic Basic KOH

  7. Order of separation

  8. interference • Gp IV sulfides are also insoluble • More soluble than gp II sulfides Ksp HgS 2 *10-53 CuS 6 *10-37 PbS 3 *10-28 Gp IV require higher [S2-] • ZnS 2 *10-25 • CoS 5 *10-22 • NiS 3 *10-20

  9. Group reagent is ……………… H2S / HCl thioacetamide / HCl 0.3M HCl (pH ≈ 0.5) CH3CSNH2 + 2H2O ⇌ CH3COOH + NH3↑ +H2S↑ 9

  10. Ppt colors SnS Bi2S3

  11. Ppt colors • IIA • IIB Gelatinous ppt • H2O2/Δ Not gelatinous 

  12. group IIB is acidic Why do we boil before adding gpII reagent? group IIA is basic Soluble thiosalts SnS2 + S2- ⇌ SnS32- (thiostannate ion) As2S3 + 3S2- ⇌ 2AsS32- (thioarsenite ion)

  13. Solubility & Order of separation

  14. Separation of mercury II Sulfides of Bi, Cd, Cu and Pb are soluble in warm dil HNO3 while HgS is insoluble. CuS + 2NO3- + 8H+ ⇌ 3Cu2+ + 3S↓ + 2NO↑ + 4H2O Aqua regia dissolves HgS readily. 3HgS + 2NO3- + 8H+ + 12Cl- ⇌ 3HgCl42- + 2NO↑ + 4H2O + 3S↓

  15. Confirmation for mercury II • HgCl42- ⇌ Hg2+ + 4Cl- • SnCl2 + 2Cl-⇌ SnCl42- • SnCl42- + 2HgCl2⇌ Hg2Cl2↓+ SnCl62- • White ppt • If more Sn2+ ions are added; Hg2Cl2 is further reduced to metallic Hg. • SnCl42- + Hg2Cl2↓ ⇌ 2Hg↓+ SnCl62- • Black ppt

  16. Interference from Cl2 Source Action How to remove? Aqua regia 2NO3- + 8H+ + 6Cl- ⇌ 3Cl2 ↑ + 2NO↑ + 4H2O Sn2+ + Cl2 ⇌ Sn4++ 2Cl- (consumes reductant)

  17. Separation of Lead All REMAINING gp IIA sulphates are soluble EXCEPT LEAD Simple addition of sulfuric acid and separation Confirmation of Lead Dissolve in ammonium acetate PbSO4 ↓+ CH3COONH4 ⇌ Pb(CH3COO)42-+ (NH4)2SO4 stable Complex ion ppt with potassium chromate Pb2+ + CrO42- ⇌ PbCrO4 ↓ • Can you predict which is least soluble? • PbSO4 PbCrO4

  18. Separation of Bismuth REMAINING gp IIA hydroxides soluble in xss Ammonia EXCEPT Bi Simple addition of excess ammonia and separation Bi3+ + 2NH4OH ⇌ Bi(OH)2+↓ + 2NH4+ White basic salt Bi(OH)2+ + NH4OH ⇌ Bi(OH)3↓ + 2NH4+ Disproportionation reaction Confirmation of Bismuth Freshly prepared tetra-hydroxostannate reagent SnCl2 + excess of NaOH 2Bi(OH)3 ↓ + 3Sn(OH)42- ⇌ 2Bi0↓ + 3Sn(OH)62- white ppt Black ppt

  19. Why are copper and cadmium hydroxides soluble in excess ammonia? • Cu2+ +t 2NH4OH ⇌ Cu(OH)2↓ + 2NH4+ • Blue ppt • Cu(OH)2 ↓ + 4NH4OH ⇌ Cu(NH3)42+ + 2OH- + 4H2O • Deep blue color • Cd2+ + 2NH4OH ⇌ Cd(OH)2↓ + 2NH4+ • Cd(OH)2 ↓ + 4NH4OH ⇌ Cd(NH3)42+ + 2OH- + 4H2O So, can u predict nxt step?

  20. Confirmation of Copper The deep blue color of [Cu(NH3)4]2+ identifies Cu2+ in the decantate. Add acetic acid + pot. Ferrocyanide brick red ppt 2Cu2+ + Fe(CN)64-⇌ Cu2Fe(CN)6↓ Confirmation of Cadmium ppt as sulfide S2- + Cd2+ ⇌ CdS ↓ Interference ?? Add KCN to decantate … what will happen? Why? Colorless [Cu(CN)4 ]3- & [Cd(CN)4 ]2- which is more stable ??

  21. Confirmation of Cd in presence of Cu KCN S2-

  22. group IIB is acidic group IIA is basic Soluble thiosalts SnS2 + S2- ⇌ SnS32- (thiostannate ion) As2S3 + 3S2- ⇌ 2AsS32- (thioarsenite ion)

  23. Solubility & Order of separation

  24. What if too strong? dilHCl As2S3, As2S5, Sb2S3, Sb2S3 and SnS2

  25. SnS2 + 6Cl- + 4H+⇌ SnCl62- + 2H2S Sb2S3 + 8Cl- + 6H+⇌ 2SbCl4- + 3H2S soluble chloro complexes As2S3 + 10NO3- + 8H+⇌ 2H2AsO4- + 3S↓ + 10NO2↑ + 2H2O MoO42- + 2H+⇌H2MoO4 Molybdic acid 3H2MoO4⇌ 2H2O + 2H+ + Mo3O102- Trimolybdate ion 3NH4+ + 10 Mo3O102- + H2AsO4- + 6 H+⇌(NH4)3As(Mo3O10)4↓ + 4H2O Ammonium arsenomolybdate

  26. Mg2+ + AsO43- + NH4+⇌ Mg (NH4) AsO4↓ Mag. Amm. Arsenate White crystalline ppt Why? If we only need Mg2+ neutralize the acid in acidic arsenate mixture without ppt Mg(OH)2 • NH4Cl • NH4OH • MgCl2

  27. Sn4+ + 2Fe0⇌ Sn0↓ + 2Fe2+ Sn0↓ + 2HCl → SnCl2 + H2 SnCl2 + 2Cl-⇌ SnCl42- 2Sb3+ + 3Fe0⇌ 2Sb0↓ + 3Fe2+ Sb0↓ + 2HCl → no reaction Why??? Electrochemical series Sb stay deposited on iron wire SnCl42- + 2HgCl2⇌ Hg2Cl2↓+ SnCl62- SnCl42- + Hg2Cl2↓ ⇌ 2Hg↓+ SnCl62-

  28. Confirmation of Sb in presence of Sn 1- Deposited on iron wire 2- ppt as orange sulfide interference from Sn Oxalic acid S2-

  29. Notes The oxidation state of As, Sb, Sn can not be decided during the analysis. It may be tested in the original sample WHY??

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