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Qualitative Analysis of Salts

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                                                                                           What is qualitative analysis?

        (a) Check the physical characteristic of the salt

        (b) Test for certain gases

        (b) The effect of the heat on the salt

        (c) Preparation aqueous salt solution to test for the cation and anion in it

        (d) Confirmatory tests for ions.         

 

 

 

 

 

                                                                                        Physical properties

        (a) physical state

        (b) colour of the salt

        (c) solubility of the salt in water

 

1. Physical state of the salt

2. Colour of the salt

 

                                  

 

3. Solubility of salt in water

 

                                  

 

        (a) Salt X insoluble in water and contains sulphate ion.

             => Salt X might be lead (II) sulphate, barium sulphate, or calcium sulphate

        (b) Salt Y soluble in water and contains carbonate ion.

              => Salt Y might be sodium carbonate, potassium carbonate, or ammonium carbonate

 

 

               

 

                                                                                               Tests for gases

        (a) is heated

        (b) reacts with dilute or concentrated acid

        (c) is heated with an alkali

                                       

 

 

 

 

 

                                                                               Effect of  heat on salts

        (a) Gas released gives information about type of anion (nonmetal ion) contains (except for ammonium salts)

        (b) Change in colour (residue left) gives information about type of cation (metal ion) contains

 

1. Effect of heat on carbonates (released carbon dioxide).

 

                                       

                                                                                           

2. Effect of heat on nitrates salt

 

                                      

3. Effect oh heat on sulphate salts

        (a) 2FeSO4.7H2O (s)        Fe2O3 (s)   +  SO2 (g)   +   SO3 (g)   +   14H2O (g)

             When iron (II) sulphate is heated strongly, it will released steam fume, slphur dioxide, sulphur trioxide and brown solid of

             iron (III) oxide is left. 

       (b) ZnSO4 (s)           ZnO (s)   +  SO3 (g)  

            CuSO4 (s)            CuO (s)   +  SO3 (g)  

            Fe2(SO4)3 (s)      Fe2O3 (s)   +  3SO3 (g)  

            When zinc sulphate, copper sulphate and iron (III) sulphate heated strongly, oxide metal and gas sulphur trioxide (acidic) are

            produced.

       (c) When ammonium sulphate is strongly heated, ammonia (alkalic) and acid sulphuric fume are released as below:

               (NH4)2SO4 (s)      2NH3 (g)   +   H2SO4 (g)

 

4. Effect oh heat on chloride salts

        (a) NH4Cl (s)         NH3 (g)   +  HCl (g)

             When ammonium chloride heated strongly, ammonia (turns damp red litmus paper into blue) and hidrogen chloride fume are

             released. When the white fume cold, white

             solid of ammonium chloride reproduced. The reaction is reversible. Hidrogen chloride is a thick white fume when touched with

             a drop of concentrated liquid ammonia.

 

 

 

 

                                                                                 Tests for anions

 

        (a) the gas released when

             (i) the salt is heated

             (ii) a dilute acid is added to the salt

        (b) the confirmatory test for specific anions that is carbonates, nitrates, sulphates and chlorides

 

1. Tests for carbonates

        MgCO3 (aq)  +   2HCl (aq)             MgCl2 (aq)   +   H2O (l)   +   CO2

        Na2CO3 (aq)  +   2HCl (aq)            2NaCl (aq)   +   H2O (l)   +   CO2

 

2. Tests for nitrates

     About 2cm3 nitrate solution is mixed with dilute sulphuric acid and iron (II) sulphate solution in a test tube. Then a few drops 

        of concentrated sulphuric acid are added slowly and carefully down rhe side of the test tube. (Do not shake the mixture!)

        brown ring is formed between the layers of concentrated acid and nitrate mixture. The brown ring composed of a complex ion,

        confirm the presence of nitrate.

 

3. Tests for chlorides

 

4. Tests for sulphates

    

 

                                                                                       

   Tests for cations

        (a) Test with aqueous sodium hydroxide, NaOH (aq)

        (b) Test with aqueous ammonia, NH3 (aq)

        (c) Confirmatory tests with specific reagents

        (a) Sodium ion, Na+

        (b) Calcium ion, Ca+

        (c) Iron (II) ion, Fe2+

        (d) Iron (III) ion, Fe3+

        (e) Copper (II) ion, Cu2+

        (f) Lead (II) ion, Pb2+

        (g) Zinc (II) ion, Zn2+

        (c) Ammonium ion, NH4+

 

                    

 

Confirmatory tests for Fe2+, Fe3+, Pb2+ and NH4+

        Pb2+   +   2I-                 PbI2 (s) (yellow precipitate)

        Pb2+   +   2Cl-               PbCl2 (s) (white precipitate)

        Pb2+   +   SO42-            PbSO4 (s) (white precipitate)

        (b) When heated, PbI2 and PbCl2 dissolves in hot water. Upon cooling PbI2 forms golden-yellow needle-like crystals,        

             while PbI2 forms white crystals.