Draw a properly electrochemical cell represented by the reaction shown below. Sh

Question

Draw a properly electrochemical cell represented by the reaction shown below. Show the direction of electron flow, write the cathode and anode half reactions as well as the shorthand notation for the cell. When 6 N HCl was added to a solution of an unknown, a white precipitate was formed. The mixture was centered and the supernatant was removed and discarded. The white ppt left behind was washed with cold water and extracted 2 times with hot water. The extracts were removed and combined, leaving behind a white ppt. A yellow precipitate was formed when some potassium chromate solution was added to the supernate. When 6 M NH_3 was added to the white ppt from A2 above, it dissolved forming a clear solution. When this solution was made distinctly acidic with 6 M nitric acid, a white ppt was formed: identify the Qualitative Gp. 1 Cations present in the unknown and write balanced equation for all reaction taking place in A1, A2 and A3.

Explanation / Answer

1. Possibilities are Ag^+, Pb^2+, Hg2^2+, and Cu^+

2,PbCl2 is fairly soluble in boiling water. Hg2Cl2, AgCl, and CuCl are not affected that much by hot water. Almost all solids are more soluble in hot water than in room temperature water. The PbCl2 solid would dissolve in the hot water leaving one of the other chlorides

3.The treatment of the precipitate from (2) with ammonia identifies the precipitate as AgCl.

AgCl(s) + 2 NH2(aq) --> [Ag(NH3)2]Cl This is soluble in ammonia solution.

If HNO3 is added the NH3 will react with HNO3 to produce NH4NO3(aq). The H^+ ions added will compete for the presence of the NH3 much better than the AgCl. The AgCl will appear again as a precipitate. Reappearance of a white precipitate confirms the presence of Ag+ in the original solution

from result

reaction

1.Ag+ +Hcl->Agcl(white precipitate)

2.Pb2+(aq) + CrO42-(aq) ==> PbCrO4(s) (yellow)

3.AgCl(s) + 2 NH2(aq) --> [Ag(NH3)2]Cl(white precipitate)

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