Identification of Cations

 

Aim: Identify the following Cations ions, Sodium, Potassium, Calcium, Iron

Identification for Na+

Test	Observation	Inference
FLAME TEST Sample moistened with HCl, introduce on platinum wire and burn on flame	Yellow color flame	Na+ ion present
Sample + potassium antimonite solution. Boil and scratch the side of the test tube with glass rod	Dense white ppt; of disodium antimonite	Na+ ion present

                                Na+    +    K2H2SbO4   -------------->   Na2H2SbO4    +    2K+ 

     

Test	Observation	Inference
To the sample solution add dilute acetic acid and magnesium urinyl acetate	Yellow crystal	Na+ ion present

     

3Na+  + 3UO2(CH3COO)2 + Mg(CH3COO)2 + CH3COOH + 4H2O ----->             3[NaMgUO2(CH3COO)2]4H2O

Identification for K+ 

     

 

Test	Observation	Inference
To the sample solution add dilute acetic acid and magnesium urinyl acetate	Yellow crystal	Na+ ion present

       

                3K+  +  Na3[CO(NO2)6] --------> 3Na+  +   K3[CO(NO2)6

 

Test	Observation	Inference
To the sample solution add concentrated solution of tartaric acid in alcohol	white ppt	K+ ion present

                       K+  +  C4H6O6 ------> H+  +  C4H5O6K

Test	Observation	Inference
Sample + picric acid	Yellow ppt	K+ ion present

Identification for Ca++ 

 

Test	Observation	Inference
Sample solution in HCl. Neutralize with NaOH and treated with ammonium carbonate	white ppt	Ca++ ion present

                 Ca ++  +  (NH4)2CO3 ----> CaCO3 + NH4+

Test	Observation	Inference
Sample solution+ ammonium oxalate	white ppt of Ca-oxalate is obtain which is soluble in HCl	Ca++ ion present

                 Ca++  +  (NH4)2(COO)2 -------> Ca(COO)2 + 2NH4+

Test	Observation	Inference
Concentrated sample solution + potassium chromate solution and shake well	Yellow crystal of Ca+  chromate which dissolve  in water.	Ca++ ion present

                Ca++  +  K2CrO4 ------->  K+  +  CaCrO4

 

Identification for Fe++ 

Test	Observation	Inference
Sample solution + potassium  ferrocyanide	white ppt which convert to blue on air oxidation	Fe++ ion present

                Fe++  +  2KFe(CN)6 ---------> K2Fe[Fe(CN)6]2

  4K2Fe[Fe(CN)6]2  +  4H+  +   O2  ----------> 4KFe[Fe(CN)6] + 4K + 2H2O 

Test	Observation	Inference
Sample aqueous solution + potassium ferrocyanide solution	Dark blue ppt which  insoluble in dil HCl but  decompose by NaOH  solution.	Fe++ ion present