Class 12 Record Experiment 18

 ANALYSIS OF SALT  5 Aluminium  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.	White residue which glows on heating	Ca2+ Mg2+ or Al3+ may be present
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)	blue tinted ash	Al3+ ions may be present 2Co(NO3)2→ 2CoO + 4NO2 + O2 Al2O3  +CoO → Al2O3 .CoO   (blue 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 ions
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	White gelatinous precipitate	PRESENCE OF GROUP III ALUMINIUM CATION CHEMISTRY  Al3+ + 3 NH4OH → Al(OH)3 (white gelatinous precipitate + 3NH4+
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+

E CONFIRMATORY TESTS FOR CATIONS IDENTIFIED UNDER GROUP ANALYSIS ALUMINIUM CATION Al3+ 

The white gelatinous precipitate is dissolved in dil.HCl. 

1. 2.

Lake test:- Added two drops of blue litmus solution and added few drops of ammonium hydroxide till blue colour develop. 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

Blue precipitate floating in the colourless solution Blue tinted ash.

Presence of aluminium cation confirmed  CHEMISTRY   Al(OH)3 (white gelatinous precipitate) + 3HCl → AlCl3 + 3H2O AlCl3 + 3NH4OH → Al(OH)3( blue colour adsorbs on this precipitate) + 3NH4Cl Presence of aluminium cation confirmed  CHEMISTRY Al2O3  +CoO→ Al2O3 . CoO   (blue ash)

RESULT

The given salt contains     Cation = Aluminium(Al3+)     Anion= Sulphate (SO42-)

Salt = Aluminium sulphate Al2 (SO4)3