ANALYSIS OF SALT 1 ( Zinc sulphate)
Experiment : - TO ANALYSE THE GIVEN SALT FOR ACIDIC RADICAL (ANION) AND BASIC RADICAL (CATION)
Theory : Two basic principles are used (i) solubility product and (ii) common ion effect.
When ionic product of a salt exceeds its solubility product, precipitation takes place and ionic product of a salt is controlled by making use of common ion effect.
Materials required: Test tubes, test tube stand, test tube holder, filter paper, watch glass, glass rod, burner, tripod stand, wire gauze, beakers, nickel spatula, reagents etc.
A) PRELIMINARY TESTS |
1. a) | Colour of the salt noted | White coloured
| absence of Cu 2+ , Fe 2+, Fe 3+, Ni 2+, Co2+, Mn2+ ions
|
b) | Smell noted : - with a drop of water rub the salt | no characteristic smell | Absence of ammonium and acetate ions |
2. | DRY HEATING TEST A small amount of the salt is heated in a dry test tube. | Yellow when hot and white when cold
| Zn2+ present CHEMISTRY:- The colour is due to nonstoichiometric metal excess defect at interstitial sites CHEMISTRY :- ZnO→Zn2+ + ½ O2(g) + 2e- Zn2+and electrons move to interstitial sites. The electrons absorb different wavelengths at different temperatures leading to different colours |
3. | FLAME TEST A little of the salt is made into a paste with conc.HCl in a watch glass and shown to the non luminous part of the flame using a glass rod. | no characteristic reaction | absence of calcium, barium, strontium or copper ions |
a | COBALT NITRATE TEST/ASH TEST To a little of the salt solution a few drops of conc. HNO3 and cobalt nitrate solution dip a filter paper into the solution and burnt into ashes(warm if needed) | green tinted ash
| i) Zn2+ ions may be present 2Co(NO3)2→ 2CoO + 4NO2 + O2 ZnO + CoO→ZnO. CoO (green ash)
|
B) IDENTIFICATION TEST FOR ANIONS |
1. | DILUTE SULPHURIC ACID TEST - A little of the salt is treated with 1 ml of dil. H2SO4 | no characteristic reaction | absence of carbonate |
2. | CONC. SULPHURIC ACID TEST - a little of the salt is added with drops of conc. H2SO4 | no characteristic reaction | Absence of nitrate, chloride and acetate
|
3. | TEST FOR SULPHATE:- BaCl2 test:- A little of the salt solution is added with few drops of BaCl2 solution and conc. HCl is added to it | White precipitate insoluble in conc. HCl
| Presence of sulphate CHEMISTRY SO42- + BaCl2 → BaSO4 (white ppt)+ 2Cl- BaSO4 (white ppt) + conc. HCl→no reaction
|
CONFIRMATORY TEST FOR SULPHATE |
Lead acetate test:- To a little of the water extract 1ml of lead acetate solution is added. | A white ppt is formed which is soluble in excess of hot ammonium acetate solution. | Presence of sulphate confirmed CHEMISTRY SO42- + (CH3COO)2Pb → PbSO4 (white ppt) + 2 CH3COO- |
D (GROUP ANALYSIS) -
Preparation of original solution – A little of the salt is mixed well with water to get original solution in a test tube
Sl. No. | EXPERIEMENT | OBSERVATION | INFERENCE |
1. | Salt + NaOH + heat | No characteristic reaction | Absence of group 0 cation ammonium NH4+ |
2. | OS + dil.HCl | No characteristic reaction | Absence of group I cations Pb2+ |
3. | OS + dil. HCl + H2S gas | No characteristic reaction | absence of group II cations Cu2+ |
4. | OS+NH4Cl + NH4OH | No characteristic reaction | Absence of group III cation Al 3+ , Fe 3+ |
5. | OS+NH4Cl + NH4OH +H2S | Dirty white precipitate
| PRESENCE OF GROUP IV CATION ZINC Zn(OH)2 + H2S → ZnS (dirty white precipitate) + 2 H2O |
6. | OS+NH4Cl+ NH4OH +(NH4)2CO3 | No characteristic reaction | Absence of group V cations Sr2+, Ba2+ , Ca2+
|
7. | OS+NH4Cl + NH4OH + ammonium hydrogen phosphate solution | No characteristic reaction | Absence of group VI cations Mg2+ |
E CONFIRMATORY TEST FOR Zn2+
1.
2.
3. | 1.Sodium hydroxide test:- To one part of the original solution add sodium hydroxide solution dropwise. A white precipitate is formed. Add more of NaOH.
Cobalt nitrate test/ash test :-To a little of the salt solution a few drops of conc. HNO3 and a few drops of cobalt nitrate solution is added in a test tube, heat the solution, dip a filter paper into the solution and burnt into ashes Potassium ferrocyanide test:- To one part of the original solution add potassium ferrocyanide solution. | The white precipitate dissolves
Green tinted ash.
White or yellowish white precipitate is formed
| Presence of zinc cation confirmed Zn2+ + 2NaOH → Zn(OH)2 ↓(dirty white precipitate) + Na+ Zn(OH)2 ↓(dirty white precipitate) + 2NaOH → Na2ZnO2(soluble) + 2H2O
Presence of zinc cation confirmed CHEMISTRY OF THE REACTION:- ZnO +CoO→ ZnO . CoO (green ash)
Presence of zinc confirmed. CHEMISTRY 2 Zn2+ + K4[Fe(CN)6] → Zn2[Fe(CN)6] (white or yellowish white precipitate) + 4K+ |
RESULT The given salt contains Cation = Zinc (Zn2+) Anion = Sulphate (SO42-)
Salt = Zinc Sulphate ZnSO4
