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JAMB Chemistry 1979 Question 38

Question 38

Qualitative Analysis

The solution of a sample in a tube will be identified as a chloride if it gives

  1. A.a white precipitate on addition of AgNO3, and barium chloride solutions
  2. B.a white precipitate when acidified with HCl, and then AgNO3 solution added
  3. C.a white precipitate when acidified with dilute HNO3 and then AgNO3 solution added.
  4. D.a white precipitate when acidified with dilute H2SO4 and then barium nitrate solution added
  5. E.a pungent smell of chlorine gas when dilute HCl and MnO2 are added.
Show the answer and explanation

Answer: C (a white precipitate when acidified with dilute HNO3 and then AgNO3 solution added.)

Explanation

Silver nitrate gives white AgCl with chloride ions; acidifying with dilute nitric acid first removes carbonate and other ions that could also precipitate. Adding HCl would itself add chloride.