Identification of Anions

 

Aim: To identify the following ions, Bicarbonates, Chlorides, Sulphates and iodides

Identification  of HCO3- :

Test	Observation	Inference
Sample + HCl  or H2SO4	Effervesence observed	HCO3- ion present

                   HCO3- + HCl  -----> H2O + CO2 + Cl-

Test	Observation	Inference
Sample + MgSO4 and boil	white ppt	HCO3- ion present

                  HCO3- + MgSO4 ------> Mg(HCO3)2 ------> MgCO3 + H2O + CO2

Test	Observation	Inference
Sample + HgCl2	white ppt	HCO3- ion present

                       

                HgCl2 + HCO3-   -------->   Hg(HCO3)2 + 2Cl-

Identification for Cl-  :

Test	Observation	Inference
Sample + Dilute HNO3+  AgNO3	white ppt	Cl- ion present

Dil. HNO3

Cl- + AgNO3 ------------------> AgCl + NO3-

Test	Observation	Inference
Take solid sample in a dry test tube. Add potassium dichromate and Sulphuric acid. Transferred the red color chromoyl chloride to another test tube containing water and lead acetate.	yellow ppt	Cl- ion present

K2Cr2O7 + 2Cl- + 6H2SO4 ---------> 6H2SO4- + 3H2O + Cr2O2Cl2

Cr2O2Cl2 + H2O --------> H2CrO4 + HCl 

Identification for SO4-- :

Test	Observation	Inference
Aqueous solution of sample; add barium chloride. Acidified with HCl.	white ppt	SO4-- ion present

                                             Dil. HCl

                       SO4-- + BaCl2 ------------> BaSO4 + 2Cl-

Test	Observation	Inference
Aqueous solution of sample; add lead acetate solution	White ppt of lead sulphate    is formed which is soluble    in ammonium acetate and     NaOH solution.	SO4-- ion present

     

SO4--  +  Pb(CH3COO)2 -------> PbSO4 + 2CH3COO- 

Identification for I- : 

 

Test	Observation	Inference
Aqueous solution of sample acidified with Sulphuric acid and potassium dichromate. Add chloroform and shake vigorously.	Chloroform layer become   violet	I- ion present

6 I- + K2Cr2O7 + 7H2SO4 --------> 3I2 + 7H2O + K2SO4 + 2CrSO4 3-

 

Test	Observation	Inference
Sample solution + KIO3 and dilute acetic acid + 1 ml of  starch mucilage.	Blue color produce	I- ion present

5 I- + 6CH3COOH + KIO3 --------> 3I2 + 6CH3COO- + 3H2O

I2 + Starch --------> blue color complex

Test	Observation	Inference
Sample + Dilute HNO3  + AgNO3	Pale tallow ppt of silver   iodide	I- ion present

dil. HNO3

I- + AgNO3 -----------------> AgI + NO3-

 

Test	Observation	Inference
Sample + DIlute HNO3    + AgNO3	Pale tallow ppt of silver iodide	I- ion present

2I- + HgCl2 ----------> 2Cl-  +  HgCl2

                                                 Red

HgCl2 + KI ---------> HgI4-