Fe3+, Al3+, Cr3+, Ni2+, Co2+, Mn2+, Zn2+ 3. GROUP CATIONS Fe3+, Al3+, Cr3+, Ni2+, Co2+, Mn2+, Zn2+

These cations precipitate as sulfides and hydroxides when reacted with hydrogen sulfide (H2S) or thioacetamide solution in basic medium buffered with NH4OH – NH4Cl. These cations do not precipitate with the reagents used for precipitation of the group I and II.cations. Group III cations are divided into two: 1) Iron Group (Group 3A): Fe3+, Al3+, Cr3+ (precipitates in the form of hydroxides). 2) Zinc Group (Group 3B): Ni2+, Co2+, Mn2+, Zn2+ (precipitates in the form of sulfides).

Systematic analysis of group III cations: 20 drops of sample containing Fe3+, Al3+, Cr3+, Ni2+, Co2+, Mn2+, Zn2+ taken into a tube from the sample. Add 10 drops of 4 M ammonium chloride (NH4Cl) solution and 10 drops of 2 M ammonium hydroxide (NH4OH, %33) solution dropwise to the sample and check the basicity of the solution with a litmus paper. Then add 20 drops of NH4OH solution and Fe3+, Al3+ and Cr3+ precipitate as their hydroxides. Heat the solution for 5 min at water bath and add 20 drops of thioacetamide solution (11%, w/v) and observe precipitates of sulfides of Ni2+, Co2+, Zn2+ and Mn2+ (COMMON PRECIPITATE) This precipitate contains Al(OH)3, Cr(OH)3, Fe(OH)3, NiS, CoS, MnS, and ZnS and it is washed several times with 0.1 M NH4Cl. Add 20 drops of 6 M HCl onto the washed precipitate. Centrifuge and separate the supernatant A and the precipitate A.

Precipitate A (CoS ve NiS): Precipitate A is taken into cruicible, heated on bunsen burber till the solute part evaporates if exist, and add 20 drops of aqua regia (15 drops of 6 M HCl + 5 drops of 6 M HNO3) to dissolve the precipitate. Add from NH4OH (%33) solution until it is basic (check with red litmus paper). Divide the solution into two parts. To the first part, add 10 drops of 0.1 M potassium ferricyanide (K4[Fe(CN)6]) solution and the dark green color is followed, which is the precipitate of cobalt ferricyanide (Co2[Fe(CN)6]). This shows the presence of Co+2. To the second part, add 2 drops of 6 M NaOH and 2 drops of dimethyl glyoxime (%1 in 96% alcohol), the rose color shows the presence of Ni+2.

Supernatant A (Fe3+, Al3+, Cr3+, Mn2+, Zn2+ ): Add 20 drops of 6 M NaOH and 20 drops of 3% H2O2 (v/v) are added to the supernatant. Centrifuge and separate supernatant B and the precipitate B. Transfer precipitate B to a clean test tube, add 10 drops of HNO3 (37.5%) and pinches of spatula sodium bismuthate (NaBiO3) from the side of the tube. The color of violet proves the presence of Mn2+. Add 0.1 M K4[Fe(CN)6] to the precipitate B, the prussian blue precipitate proves the presence of Fe3+.

Supernatant B (Zn2+, Al3+, Cr3+): Add 20 drops of HNO3 and NH4OH to the solution until it is basic. Centrifuge and separate the supernatant C and the precipitate C Precipitate C is white aluminum hydroxide (Al(OH)3). The yellow color of the supernatant C, which contains Cr3+ and Zn2+, indicates the presence of Cr3+. Add 20 drops of 2 M CH3COOH to the supernatant C to make the medium acidic. Add pinches of spatula of sodium acetate (NaCH3COO). Heat the solution in a water bath for 20 min and add 2 drops of 0.5 M barium chloride (BaCl2) solution to the hot solution. The formed yellow precipitate (precipitate D) is barium chromate (BaCrO4). Add 2 drops of thioacetamide solution (11% w/v) to the supernatant D and heat it up in the water bath with stirring for 5 minutes until the white precipitate is visible. The formation of dirty white zinc sulfide (ZnS) shows the presence of Zn2+.

Al(OH)3, Cr(OH)3, Fe(OH)3, NiS, CoS, MnS, ZnS SUPERNATANT A: (Fe3+, Al3+, Cr3+, Mn2+, Zn2+ ) dark green color Co +2 Transfer to a clean test tube 10 drops of HNO3 pinches of spatula sodium bismuthate (NaBiO3) from the side of the tube PRECIPITATE A: CoS, NiS III. GROUP CATIONS 20 drops of sample 10 drops of 4 M NH4Cl Dropwise 2 M NH4OH check the basicity of the solution with a litmus paper. 20 drops of NH4OH eklenir. Heat the solution for 5 min at water bath and add 20 drops of thioacetamide solution COMMON PRECIPITATE Al(OH)3, Cr(OH)3, Fe(OH)3, NiS, CoS, MnS, ZnS Wash several times with 0.1 M NH4Cl Add 20 drops of 6 M HCl Centrifuge and separate the supernatant A and the precipitate A. aken into cruicible, heated on bunsen burber till the solute part evaporates 20 drops of aqua regia (15 drops of 6 M HCl + 5 drops of 6 M HNO3) to dissolve the precipitate. Add 2 M NH4OH check the basicity with red litmus paper. 2 drops of 6 M NaOH 2 drops of dimethyl glyoxime Add 0.1 M (K4[Fe(CN)6]) SUPERNATANT C: Cr3+, Zn2+ Violet color, Mn2+ white aluminum hydroxide (Al(OH)3) 2 drops of thioacetamide solution heat it up in the water bath with stirring for 5 minutes until the white precipitate is visible. 20 drops 2 M CH3COOH pinches of spatula of sodium acetate (NaCH3COO) Heat the solution in a water bath for 20 min add 2 drops of 0.5 M barium chloride (BaCl2) solution to the hot solution. 20 drops of 6 M NaOH 20 drops of 3% H2O2 Centrifuge and separate supernatant B and the precipitate B. PRECIPITATE B Fe(OH)3, MnO2 20 drops of HNO3 add NH4OH until it is basic. Centrifuge and separate the supernatant C and the precipitate C SUPERNATANT B: Zn2+, Al3+, Cr3+ 10 drops of 0,1 M (K4[Fe(CN)6]) rose color Ni +2 prussian blue precipitate Fe3+ PRECIPITATE C PRECIPITATE D Yellow precipitate barium chromate BaCrO4 SUPERNATANT D dirty white precipitate ZnS Divide the sample into two

Al(OH)3, Cr(OH)3, Fe(OH)3, NiS, CoS, MnS, ZnS SUPERNATANT A: (Fe3+, Al3+, Cr3+, Mn2+, Zn2+ ) dark green color Co +2 Transfer to a clean test tube 10 drops of HNO3 pinches of spatula sodium bismuthate (NaBiO3) from the side of the tube PRECIPITATE A: CoS, NiS III. GROUP CATIONS 20 drops of sample 10 drops of 4 M NH4Cl Dropwise 2 M NH4OH check the basicity of the solution with a litmus paper. 20 drops of NH4OH eklenir. Heat the solution for 5 min at water bath and add 20 drops of thioacetamide solution COMMON PRECIPITATE Al(OH)3, Cr(OH)3, Fe(OH)3, NiS, CoS, MnS, ZnS Wash several times with 0.1 M NH4Cl Add 20 drops of 6 M HCl Centrifuge and separate the supernatant A and the precipitate A. aken into cruicible, heated on bunsen burber till the solute part evaporates 20 drops of aqua regia (15 drops of 6 M HCl + 5 drops of 6 M HNO3) to dissolve the precipitate. Add 2 M NH4OH check the basicity with red litmus paper. 2 drops of 6 M NaOH 2 drops of dimethyl glyoxime Add 0.1 M (K4[Fe(CN)6]) SUPERNATANT C: Cr3+, Zn2+ Violet color, Mn2+ white aluminum hydroxide (Al(OH)3) 2 drops of thioacetamide solution heat it up in the water bath with stirring for 5 minutes until the white precipitate is visible. 20 drops 2 M CH3COOH pinches of spatula of sodium acetate (NaCH3COO) Heat the solution in a water bath for 20 min add 2 drops of 0.5 M barium chloride (BaCl2) solution to the hot solution. 20 drops of 6 M NaOH 20 drops of 3% H2O2 Centrifuge and separate supernatant B and the precipitate B. PRECIPITATE B Fe(OH)3, MnO2 20 drops of HNO3 add NH4OH until it is basic. Centrifuge and separate the supernatant C and the precipitate C SUPERNATANT B: Zn2+, Al3+, Cr3+ 10 drops of 0,1 M (K4[Fe(CN)6]) rose color Ni +2 prussian blue precipitate Fe3+ PRECIPITATE C PRECIPITATE D Yellow precipitate barium chromate BaCrO4 SUPERNATANT D dirty white precipitate ZnS Divide the sample into two

When excess NH3 is added to the starting solution, red brown color indicates the presence of the Fe3+, and/or colorless and gelatinous precipitate indicates the presence of Al3+.