Laboratory Exercise # 4 ANALYSIS OF GROUP II CATIONS (ACID HYDROGEN SULFUR GROUP) INTRODUCTION : Group II cations are also called Copper-Arsenic group. This is further divided into 2 groups: Copper Group which consists Hg 2+ , Pb 2+ , Cu 2+ , and Cd 2+ and Arsenic group which consists of As 3+ , As 5+ , Ab 3+ , Sb 5+ , Sn 2+ , and Sn 4+ . The cations of these group have an affinity to sulfur and tend to form covalent bonds with sulfide, S 2- , forming colored or black compounds: Compound Color SnS 2 Yellow Sb 2 S 3 Orange Bi 2 S 3 Black or Dark brown HgS Black Cu 2+ also yields the following colors with S 2- : blue for CuSo4.5H2O and green for CuSO4. Antimony (Sb) and Tin (Sn) are on the borderline between metal and nonmetal and form complexes with S 2-- . Their sulfides are acidic. Cadmium (Cd) and Arsenic are limited in this analysis due to their hazardous nature. 2 Bi 3+ + 3H 2 S Bi 2 S 3 + 6H + Cu + + H 2 S CuS + 2H + Hg 2+ + H 2 S HgS + 2H + 2Sb 3+ + 3H 2 S Sb 2 S 3 + 6H + Sn 4+ + 2H 2 S SnS 2 + 4H + LEARNING OUTCOMES : After completing the activity, students will be able to: 1. accurately perform the different procedures in identifying the Group II cations. 2. correctly identify the different cations in the group through its chemical reactions. MATERIALS:
o Centrifuge o Chemicals: o 50 ml distilled water o (12) 10 ml Test tubes o 30 ml Group II cations o 30 ml 1M NH 4 OH o Test tube rack o 30 ml 5% Thioacetamide solution o 30 ml 1M HCl o Test tube holder o 30 ml 3M HNO 3 o 30 ml 6M HCl o Stirring rod o 15 ml 6M HNO 3 o 10 ml 1M NH 4 NO 3 o Hot plate o 10 ml concentrated NH 4 OH o Aluminum wire/foil o Beaker o 10 ml concentrated HAC o 10 ml Sodium stannite o Evaporating dish o 10 ml 0.2M HgCl 2 o 10 ml 0.1M K 4 Fe(CN) 6 o Water bath o 10 ml 1M SnCl 2 o 10 ml 3% H 2 O 2 o Litmus paper o 15 ml 3M NH 4 OH o 10 ml 1M Oxalic acid o 10 ml 5% NaClO o 10 ml 0.1 M HCl PROCEDURE : Separation and Identification of Group II Cations A. Precipitation of the Group II cations: 1. In a test tube, add 10 drops of 3M HNO 3 to 1 ml of known solution and evaporate just enough to end with a moist residue. 2. Cool and add 20 drops of water. Add 1M NH 4 OH dropwise until just basic to litmus. 3. Then add 1M HCl until the solution becomes acidic to litmus. 4. Add 4 drops of 6M HCl and dilute the solution to 3 ml. 5. Add 20 drops of 5% thioacetamide solution. 6. Heat the test tube with the solution in the water bath for 10 minutes. 7. Add 2 ml of water and heat for another 5 minutes. 8. Centrifuge and discard the supernatant. 9. Wash precipitate twice with 20 drops of 0.1M HCl and discard washings. B. Separation of ions into Group A and B: 1. To the precipitate in step A, add 30 drops of 3M NH 4 OH and 8 drops thioacetamide solution. 2. Heat the mixture in a hot water bath for 5 minutes. 3. Centrifuge and reserve the supernatant in a separate test tube.
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- Summer '19
- Solubility, Sulfide, Hydrogen sulfide, Group II Cations