ANALYSIS OF SALT 4 (Lead acetate)
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 | vinegar like smell | acetate CH3COO- salt may be present CHEMISTRY:- On rubbing the acetate salts liberate acetic acid vapours which has characteristic vinegar smell |
2. | DRY HEATING TEST A small amount of the salt is heated in a dry test tube. | Smell of acetic acid or vinegar
| Presence of acetate salt CHEMISTRY :- On heating acetic acid vapours are liberated which gives vinegar smell |
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) | no characteristic coloured ash | absence of zinc, magnesium, aluminium ions |
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 salt
|
2. | CONC. SULPHURIC ACID TEST - a little of the salt is added with drops of conc. H2SO4 | colourless vapours with smell of vinegar turns blue litmus red
| Presence of acetate CHEMISTRY CH3COO- + H2SO4→ CH3COOH+ HSO4- acetic acid has vinegar smell and turns blue litmus red |
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 | no characteristic reaction | Absence of sulphate |
CONFIRMATORY TEST FOR ACETATE |
1. Ester test:- To a little of the salt is warmed with drops of conc. H2SO4. Added 1ml ethyl alcohol. Shaken and poured the contents into a beaker containing cold water.
2. Oxalic acid test:- Take a small quantity of the salt on a watch glass and mix it with solid oxalic acid and make a paste with few drops of water. Rub the paste and smell. |
Pleasant fruity smell of ester
Smell of vinegar or acetic acid |
Presence of acetate confirmed CHEMISTRY CH3COOH + C2H5OH → CH3COO C2H5(fruity smell) + H2O
Presence of acetate confirmed
CHEMISTRY :- H2C2O4 (oxalic acid) + 2CH3COO-→ C2O42- + 2 CH3COOH |
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 NH4+ |
2. | OS + dil.HCl | White precipitate which is soluble in hot water when boiled but reappears on cooling is obtained.
| Presence of group I cations Pb2+ CHEMISTRY Pb2+ + 2HCl → PbCl2 + 2H+ The white ppt is lead chloride which is soluble in hot water but insoluble in cold water |
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 | No characteristic reaction | Absence of group IV cations Zn2+ ,Ni,2+ Co2+ and Mn2+ |
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+ |
GROUP 1 CONFIRMATORY TEST FOR LEAD CATION Pb2+
1.
2. | potassium iodide test:- To one ml of the original solution added few drops of KI solution
potassium chromate test:- To one ml of the original solution few drops of potassium chromate solution is added | Yellow precipitate which is soluble on boiling but reappears as golden spangles on cooling
Yellow precipitate
| lead ion confirmed CHEMISTRY PbCl2 + 2KI → PbI2 (yellow precipitate) + 2Cl-
lead cation confirmed CHEMISTRY K2CrO4 + Pb2+ → PbCrO4(yellow ppt) + 2K+ |
RESULT The given salt contains Cation = lead (Pb2+) Anion = Acetate ( CH3COO-)
Salt = lead acetate (CH3COO)2Pb
