4. A student, in analyzing a Group l unknown, makes the following observations.

Question

4. A student, in analyzing a Group l unknown, makes the following observations. Indicate which ions are definitely present, which are absent and which are questionable (might be present or absent). Note that in this problem and others like it throughout this text, confirmatory test are ordinarily not included. The precipitate formed when HCl is added to the unknown is partially soluble in hot water. The ppt (precipitate) remaining is completely soluble in 6 M NH3 (2) Ag (2) Hg22 definitely present definitely absent definitely present definitely absent definitely presentdefinitely absent questionable questionable questionable +2

Explanation / Answer

Answer

Ag+    Definetely present

Hg22+   Definetely apsent

Pb2+ Questionable

Explanation

While heating the precipitate formed by adding HCl is dissolved in hot water.Lead chloride will dissolve in hot water but Silverchloride and Mercurous chloride remain undissolved in hot water.So, by this observation we can conclude Pb2+ may be present

Remaining precipitate from the hot water test is dissolved in 6M NH3. Siver chloride will dissolve in 6M NH3 by forming soluble complex [Ag(NH3)]+ at the same time Mercury chloride react to NH3 to form precipitate of mercury

AgCl(s) + 2NH3 (aq) - - - - - > [Ag(NH3)]Cl (aq)

Hg2Cl2(s) + 2NH3(aq) - - - - > Hg(s) + HgNH2Cl(s) + Cl-(aq) So, we can conclude Ag+ definetlypresent and Hg22+ definety absent

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