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2. An unknown containing cations from Group I was treated with HCI. A white prec

ID: 979653 • Letter: 2

Question

2. An unknown containing cations from Group I was treated with HCI. A white precipitate formed, which appeared to be completely insoluble in hot water. The precipitate dissolved completely in NH3 to leave a clear solution. What ion(s) must be present (although still in need of confirmation)? What ion(s) seem to be absent? What must be done to confirm the absence of this/these ion(s)? Now that you have figured out what was in the unknov equations for each of the observations made during the analysis.

Explanation / Answer

The white precipitate can be of Hg2+ , Ag+ , or Pb+2

the salts which are insoluble in hot water will be of Hg2+ , Ag+

The salt is again soluble in ammonia so this must be Ag+

Ag+ + Cl- ---> AgCl (white ppt)

AgCl ---> insoluble in hot water

AgCl + 2NH3 --> Ag(NH3)2+ (soluble in water)