Write the procedure to identify the cation and anion in ammonium carbonate or aluminum chloride salt.
Answers
1) For ammonium carbonate:
Cation:
=>Smell the salt after adding distilled water to it.
Observation: An ammoniacal smell is observed.
Conclusion: NH4+ may be present.
=> Add small quantity of NH4OH solution.
Observation: No precipitate is observed.
Conclusion: Na+, K+ or NH4+ may be present. Excess NH4OH is not added.
=>Add small quantity of NaOH solution.
Observation: A gas with a pungent, ammoniacal odour is evolved that turns moist red litmus blue and gives dense white fumes with a glass rod dipped in concentrated HCl.
Conclusion: NH4+ is confirmed. No need to add excess NaOH.
=> Add a small quantity of concentrated NaOH and Nessler's reagent to the salt and heat if required.
Observation: The Nessler's reagent turns brown and a brown precipitate may also be produced.
Conclusion: NH4+ is present in the given salt.
Anion:
=>Add dilute sulphuric acid.
Observation: A gas is evolved with a brisk effervescence( bubbling). The gas turns moist blue litmus faint red, turns limewater milky but shows no effect with acidified pink Potassium permanganate solution.
Conclusion: The anion present in the given salt is Carbonate (CO3-2).
Inference: The name of the salt is Ammonium Carbonate (NH4)2CO3.
2) For Aluminium chloride:
Anion:
=>Add dilute sulphuric acid.
Observation: No gas is evolved, no effervescence or precipitate is seen.
Conclusion: NO3-1 or Cl-1 may be present in the salt.
=> Add conc. sulphuric acid.
Observation: A gas is evolved that fumes in moist air, turns moist blue litmus red, gives dense white fumes with a glass rod dipped in NH4OH solution and when bubbled through Silver nitrate solution gives a curdy white precipitate soluble in excess ammonium hydroxide and insoluble in dilute nitric acid.
Conclusion: Chloride anion is confirmed.
Cation:
=> Smell the salt after adding distilled water to it.
Observation: No ammoniacal smell is noticed.
Conclusion: NH4+ is not present.
=> Add NaOH solution dropwise to the salt soln. till in excess.
Observation: A gelatinous white precipitate is observed which is soluble in excess NaOH solution.
Conclusion: The hydroxide of the cation is amphoteric in nature, Al3+, Pb2+ or Zn2+ may be present.
=> Add NH4OH solution dropwise to the salt soln. till in excess.
Observation: A gelatinous white precipitate is observed which is insoluble in excess NH4OH solution.
Conclusion: Al3+ or Pb2+ may be present.
=> Take the salt solution and add dilute hydrochloric acid, concentrated nitric acid and boil it, after cooling add NH4OH.
Observation: A gelatinous white precipitate is observed.
Conclusion: Al3+ may be present in the given salt.
=>Dissolve the precipitate formed in hydrochloric acid, then add blue litmus solution, now add some NH4OH solution.
Observation: The gelatinous white precipitate dissolves in the dilute hydrochloric acid, blue litmus solution turns red as it is acidic, gelatinous white precipitate is formed once again on adding NH4OH solution which absorbs blue colour due to alkaline nature of NH4OH and floats as an insoluble blue complex on the surface.
Conclusion: Al3+ cation is confirmed.
Inference: The name of the salt is Aluminium chloride [AlCl3].
1) For ammonium carbonate:
Cation:
=>Smell the salt after adding distilled water to it.
Observation: An ammoniacal smell is observed.
Conclusion: NH4+ may be present.
=> Add small quantity of NH4OH solution.
Observation: No precipitate is observed.
Conclusion: Na+, K+ or NH4+ may be present. Excess NH4OH is not added.
=>Add small quantity of NaOH solution.
Observation: A gas with a pungent, ammoniacal odour is evolved that turns moist red litmus blue and gives dense white fumes with a glass rod dipped in concentrated HCl.
Conclusion: NH4+ is confirmed. No need to add excess NaOH.
=> Add a small quantity of concentrated NaOH and Nessler's reagent to the salt and heat if required.
Observation: The Nessler's reagent turns brown and a brown precipitate may also be produced.
Conclusion: NH4+ is present in the given salt.
Anion:
=>Add dilute sulphuric acid.
Observation: A gas is evolved with a brisk effervescence( bubbling). The gas turns moist blue litmus faint red, turns limewater milky but shows no effect with acidified pink Potassium permanganate solution.
Conclusion: The anion present in the given salt is Carbonate (CO3-2).
Inference: The name of the salt is Ammonium Carbonate (NH4)2CO3.
2) For Aluminium chloride:
Anion:
=>Add dilute sulphuric acid.
Observation: No gas is evolved, no effervescence or precipitate is seen.
Conclusion: NO3-1 or Cl-1 may be present in the salt.
=> Add conc. sulphuric acid.
Observation: A gas is evolved that fumes in moist air, turns moist blue litmus red, gives dense white fumes with a glass rod dipped in NH4OH solution and when bubbled through Silver nitrate solution gives a curdy white precipitate soluble in excess ammonium hydroxide and insoluble in dilute nitric acid.
Conclusion: Chloride anion is confirmed.
Cation:
=> Smell the salt after adding distilled water to it.
Observation: No ammoniacal smell is noticed.
Conclusion: NH4+ is not present.
=> Add NaOH solution dropwise to the salt soln. till in excess.
Observation: A gelatinous white precipitate is observed which is soluble in excess NaOH solution.
Conclusion: The hydroxide of the cation is amphoteric in nature, Al3+, Pb2+ or Zn2+ may be present.
=> Add NH4OH solution dropwise to the salt soln. till in excess.
Observation: A gelatinous white precipitate is observed which is insoluble in excess NH4OH solution.
Conclusion: Al3+ or Pb2+ may be present.
=> Take the salt solution and add dilute hydrochloric acid, concentrated nitric acid and boil it, after cooling add NH4OH.
Observation: A gelatinous white precipitate is observed.
Conclusion: Al3+ may be present in the given salt.
=>Dissolve the precipitate formed in hydrochloric acid, then add blue litmus solution, now add some NH4OH solution.
Observation: The gelatinous white precipitate dissolves in the dilute hydrochloric acid, blue litmus solution turns red as it is acidic, gelatinous white precipitate is formed once again on adding NH4OH solution which absorbs blue colour due to alkaline nature of NH4OH and floats as an insoluble blue complex on the surface.
Conclusion: Al3+ cation is confirmed.
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