BORATORY 33 QUESTIONS 1. Write net-ionic equations for all the reactions occurri

Question

BORATORY 33 QUESTIONS 1. Write net-ionic equations for all the reactions occurring in the Group I analysis for each cation in the group (regardless of which ions were present in your particular unknown). Write all the reactions for lead, then all those for mercury, then all those for silver. Show the physical form of all species (og.(), (ag). etc.). Underlin ll solids. ecros Silver: Ag+(w' clan) AgCl(s) "until acidic to litmus." Explain why it is important to add enough 6 M HNO to make the solution acidic in order to get a positive test. 2. In Step 5 of the procedure ("Test for Silver), you were told to add 6 M HNO,

Explanation / Answer

Hi you are already completed 1st question and is correct set of net ionic equations.

2. Answer:

Confirmation of the presence of silver: It is now necessary to consider the precipitate which may be comprised of AgCl or Hg2Cl2 or a mixture of the two. By adding NH4OH to the solution, the AgCl and Hg2Cl2 can be separated.

AgCl + 2 NH4OH --> Ag(NH3)2+ + Cl- + 2H2O

Hg2Cl2 + 2NH4OH --> Hg(black) + Hg(NH2)Cl(white) + 2H2O + NH4+ + Cl-

This type of reaction seen with Hg22+ is called a disproportionation reaction where the Hg2Cl2 oxidizes and reduces itself to Hg (black) and Hg(NH2)Cl (white). The mix of the two gives a grey precipitate that may be masked in the presence of white AgCl precipitate.

If the entire chloride precipitate dissolves, then only AgCl was in the precipitate as Hg2Cl2 is not soluble in NH4OH. If the white precipitate changes to black or grey, then Hg2Cl2 was present but we do not yet know if there was any AgCl. HNO3 can be added to the supernatant once the precipitate and liquid have been separated. If AgCl is present, it will have dissolved and be in the liquid portion. Adding the nitric acid will cause the white AgCl to precipitate out according to the following reaction.

Ag(NH3)2+ + Cl- + 2H+ --> AgCl(white) + 2NH4+

Regardless the filtrate collected is acidify to litmus with 6M HNO3 added dropwise until a white precipitate reappears, then Ag+ ion is confirmed present in the unknown.

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