E-Storeprinciples related to practical Chemistry
Tests For Cations
| Zero | NH4+ | NaOH and Nessler’s Reagent | Brown Precipitate |
| I Group | Pb2+ | Salt Solution and dil. HCl | White Precpitate |
| II Group | Pb2+ Cu2+ Cd2+ | Salt Solution , dil HCl and H2S | Black Precipitate Black Precipitate Yellow Precipitate |
| III Group | Al3+ Fe3+ Mn2+ | Salt solution is treated with NH4Cl solid followed by NH4OH | Gelatinous White ppt. Gelatinous Brown ppt. White turning Brown on standing. |
| IV Group | Mn2+ Zn2+ Ni2+ | Salt solution is treated with NH4Cl solid followed NH4OH and H2S. | Buff or Pale pink ppt Dull white ppt Black ppt |
| V Group | Ba2+ Ca2+ | Salt solutions is treated with NH4Cl followed byNH4OH and (NH4)2CO3 | White ppt White ppt |
| VI Group | Mg2+ | Salt solutions is treated with NH4Cl followed byNH4OH and (NH4)2HPO4 | White ppt |
| Preparation of Original Solution . The mixture should be dissolved in an suitable solvent. The choice of solvents can have the following sequence.1.Cold Water, 2. Warm water, 3. Dilute HCl, 4. Concentrated HCl, 5. Dilute HNO3, 6. Concentrated HNO3, and 6. Aquaregia. The solution prepared by dissolving the mixture in the solvent is referred to a the original solution or O.S. |
| | EXPERIMENT | OBSERVATION | INFERENCE | |
| 0 Group | | | | |
| | Shake the aqueous mixture solution well with NaOH and note the odour. | Smell of Ammonia NH3 | Presence of NH4+ indicated | |
| | To one ml of Nesslers (K2[HgI4]) reagent add aqueous mixture solution | Brown precipitate of Mercuric Amido Iodide (NH2.HgO.HgI) is obtained. | NH4+ Confirmed | |
| I Group | | | | |
| | A) White Precipitate. Dissolve the above precipitate in hot water and perform the following tests | The white ppt. of PbCl2 is soluble in hot water Pb2+ + 2Cl-® PbCl2 | Pb2+ may be present | |
| | (i) Treat a part of the above solution with K2CrO4 solution | Yellow precipitate due to the formation of PbCrO4. Pb2+ + CrO4® PbCrO4. | Pb2+ Present | |
| | (ii) To another part of group one solution add KI solution | Yellow precipitate due to the formation of PbI2 which is soluble in hot water reappears as golden spangles on cooling Pb2+ + I-® PbI2 | Pb2+ Confirmed | |
| II Group | | | | |
| | Black Precipitate.(NiS). Dissolve the group II black residue in dil HNO3 and perform the following tests. |
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| | a) If the solution is blue perform the following tests. (i) Add NH4OH drop wise until it is in excess. | Blue precipitate is formed which dissolves in excess of the reagent. Cu2+ + 2OH-® Cu(OH)2 Cu(OH)2 + 4NH4OH ® [Cu(NH3)4](OH)2 + 4H2O. | Cu2+ | |
| | (ii) Acidify the second portion with acetic acid and add potassium Ferrocyanide. | Reddish brown precipitate is obtained. 2Cu2+ + [Fe(CN)6]4-® Cu2[Fe(CN)6] | Cu2+ | |
| | b) If the solution is colour less perform the following tests. (i) Add KI to one part of the above solution. | Yellow precipitate due to the formation of PbI2 which is soluble in hot water reappears as golden spangles on cooling. Pb2+ + 2I-® PbI2 | Pb2+ Confirmed | |
| | (ii)Add K2CrO4 to another part of the solution | Yellow precipitate due to the formation of PbCrO4 Pb2+ + CrO42-® PbCrO4 | Pb2+ Confirmed | |
| III Group | | | | |
| |
Dissolve the white gelatinous precipitate by boiling with NaOH solution and divide it into two parts. | | | |
| | (i) To the first part add NH4Cl and boil | White precipitate | Al3+ present | |
| | (ii) To the second part add dil. HCl ,litmus solution and excess of NH4OH | A blue lake | Presence of Al3+ confirmed. | |
| | Ash test: Group III residue + 3 drops of conc. HNO3 + 3 drops of Cobalt nitrate. Dip a rolled filter paper in this solution and burn in the flame | A Blue tinted ash is obtained. 2Al(OH)3 ® Al2O3 + 3H2O. 2 Al2O3 + 2Co(NO)3 ® 2CoO.Al2O3 + 4NO2 + O2 | Presence of Al3+ confirmed. | |
| | B) Gelatinous brown ppt. Fe(OH)3. Dissolve the ppt. in dil HCl and divide it into two parts. | | | |
| | (i) To one part of the above precipitate add Potassium Ferrocyanide solution. | A blue (Prussian blue) coloured solution or precipitate is formed. Fe3++ 3 [Fe(CN)6]4-® Fe4[Fe(CN)6]3 | Presence of Fe3+ indicated. | |
| | (ii) To the second part add Potassium thiocyanide. | Blood red coloration Fe3+ + 3CNS-® Fe(CNS)3 | Presence of Fe3+ confirmed. | |
| IV Group | | | | |
| | A) Black precipitate. (NiS) Conformation for Ni2+ Dissolve the black precipitate in dil. HCl add NH4Cl and NH4OH and divide into two parts: | | Presence of Ni2+ | |
| | (i) To the first part add Dimethyl Glyoxime | Rose Red Precipitate. | Presence of Ni2+ Confirmed. | |
| | (ii) Through the second part pass H2S gas. | A black precipitate is formed | Presence of Ni2+ Confirmed. | |
| | B)DullWhite precipitate. Conformation for Zn2+ Dissolve the white ppt. in dilute HCl, to this solution NaOH is first added in drops then in excess until the ppt. dissolves. | | | |
| | (i) To one part add Acetic acid and potassium Ferrocyanide. | White precipitate is formed. Zn2+ + [Fe(CN)6]4-® Zn2[Fe(CN)6] | Presence of Zn2+ confirmed. | |
| | (ii) Pass H2S and filter | White precipitate is formed | Presence of Zn2+ confirmed. | |
| | Ash test: Group IV residue + 3 drops of conc. HNO3 + 3 drops of Cobalt nitrate. Dip a rolled filter paper in this solution and burn it in the non luminous part of the flame. | Green tinted ash is formed. | Presence of Zn2+ confirmed | |
| | C) Conformation of Mn2+. Buff precipitate is heated with PbO2 and conc. HNO3 and dilute with water. | The supernatent liquid turns pink due to the formation of permanganic acid. 2Mn(NO3)2 + 5PbO + 6HNO3 ® 5Pb(NO3)2 + 2HMnO4 + 2H2O | Presence of Mn2+ is confirmed. | |
| V Group | | | | |
| | White precipitate: Dissolve the group V precipitate in minimum quantity of Acetic acid and divide into three parts. Keep aside a part of the group precipitate for Flame test. | | | |
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| A Yellow precipitate is formed. Ba2+ + CrO42-® BaCrO4 | Presence of Ba2+ Ba2+ confirmed. | |
| | · To the third part add Ammonium Oxalate | A White precipitate is formed. Ca2+ + C2O42-® Ca C2O4 | Presence of Ca2+ confirmed | |
| | Flame test: The group V residue is treated with conc. HCl and a Nichrome / Platinum wire dipped in the above solution is shown into the non luminous part of the flame. | a) Apple Green flame b) Brick Red Flame | a) Ba2+ Confirmed b) Ca 2+ confirmed | |
| VI Group | | | | |
| | White Crystalline ppt. Group VI ppt. is dissolved in minimum quantity of dil HNO3 and few drops of conc. HNO3 and Cobalt Nitrate are added. A rolled filter paper is dipped in the above solution and burned in the non luminous part of the flame. | A pink tinted ash is obtained. | Presence of Mg2+ is confirmed. | |
| | Magneson reagent test: The group VI residue is dissolved in dil. HCl to this a few drops of Magneson reagent is added followed by NaOH. | A blue precipitate is formed. | Presence of Mg2+ is confirmed. | |
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