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identifying cation and anion in the given salt.

identifying cation and anion in the given salt.

Grade:12

2 Answers

Akshay Meena
askIITians Faculty 34 Points
10 years ago

Well PRASAD For identifying cation and anion in the given salt . You have to go through the very long list of testing and for a particular ion we have different approach in qualitative analysis. For now, I am just providing you an example that clear your thought about diffentiating or identifying the ions in the given salt.

Lets say Someone just give us a salt wrapped in a paper and we have to identifying it so the process is like this :

  1. First the very natural test Visual test : yellow / brown solid - The color of the solid is characteristic of the Fe3+ ion.
  2. Heat test   : no reaction
  3. Flame test : no reaction
  4. Solubility in water: soluble
  5. Soluble in Nitric acid: soluble
  6. Reaction with Sodium hydroxide: formed an insoluble white precipitate which did not redissolve in excess NaOH -- White ppt with hydroxide, it eliminates the alkali metals, Ca, strontium, and Ba. Since the cation is not amphoteric, it also eliminates Al, Cr, Pb, Zn, and Sn.
  7. Reaction with Ammonia: Formed an insoluble white precipitate which did not redissolve in excess NH3 ---
    By this test we can eliminate those metal which do not form ammonium complex which eliminates Ni, Cu(II), Ag, Cd
  8. Reaction with Hydrochloric acid: No reaction ---- That eliminates Hg also, Now out of the left cation list there may be a chance Fe is there in the salt. But for conforming Fe we can do one (Specific Iron Test) test.
  9. Specific Iron Test --> formation of a thiocyanate complex with SCN-  : Solution turned blood red -- Fe Confirmed by this reaction:  Fe+3 + SCN- ----> Fe(SCN)2+
  10. Reaction with Silver nitrate : Formed an insoluble white precipitate --- It gives us a confirmation about the presence of either chloride, bromide, or iodide. Although the colors are different (AgCl white, AgBr cream, AgI yellow). That means we have to perform a special test to make sure that which anion is prtesent in the salt.
  11. Specific Chloride, Bromide, Iodide Test : PPt dissolved in addition of ammonia --- That gives us a very concrete result :   Ag+(aq) + Cl-(aq) → AgCl(s)
                 AgCl(s) + 2 NH3(aq) → Ag(NH3)2+(aq) + Cl-(aq)Analysis of observations:

Conclusion: Sample  is FeCl3

So,You can see by urself that for finding out just Fe+3 , Cl- we have to perform 11 test method , So For sample containing different ion we have to perform different specific test but have to go through with same process. For list of test you can just read Oualitative Analysis of salts in any common book of Inorganic Chemistry.

 

Thanks & Regards
Akshay Meena, 
askIITians Faculty
M.Tech, IIT Kharagpur
kiran kumar
34 Points
10 years ago

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