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10 Nov 2019
Qualitative Analysis of Group I Cations Precipitation and Separation of Group I Ions The chlorides of Pb, Hg", and Ag' are all insoluble in cold water. They can be removed as a group from solution by the addition of HC1. The reactions that occur are simple precipitations Ag+(aq) + CI-(aq) â AgCl(s) Pd2+(aq) + 2 Cã(aq) â PbCl2(s) He (ag) + 2 C (a)H Cl,) It is important to add enough HCI to ensure complete precipitation, but not too large an excess. In concentrated HCI solution these chlorides tend to dissolve, producing chloro-complexes such as A Lead chloride is separated from the other two chlorides by heating with water. The PbCl, dissolves in hot water by the reverse of Reaction 2: Phats) â Pb2+ (aq) + 2 cr(aq) Once Pb2+ has been put into solution, we can check for its presence by adding a solution of Koro, The chro- mate ion, Cro.. gives a yellow precipitate with Pb yellow The other two insoluble chlorides, AgCI and Hg Cl, can be separated by adding aqueous ammonia. Silver chloride dissolves, forming the complex ion Ag(NH): AgCl(s) + 2 NHfaq) â Agt NH),'(aq) + Cr(aq) Ammonia also reacts with Hg,Cl, via a rather unusual oxidation-reduct finely divided metallic mercury, which is black, and a compound of formula HgNH,CI, which is white: ion reaction. The products include HE:Cl2(s) + 2 NH, (aq) â Hg(1) + HgNH,CIS) + NH,' (aq) + Cr(aq) black white white As this reaction occurs, the solid appears to change color, from white to black or gray
Qualitative Analysis of Group I Cations Precipitation and Separation of Group I Ions The chlorides of Pb, Hg", and Ag' are all insoluble in cold water. They can be removed as a group from solution by the addition of HC1. The reactions that occur are simple precipitations Ag+(aq) + CI-(aq) â AgCl(s) Pd2+(aq) + 2 Cã(aq) â PbCl2(s) He (ag) + 2 C (a)H Cl,) It is important to add enough HCI to ensure complete precipitation, but not too large an excess. In concentrated HCI solution these chlorides tend to dissolve, producing chloro-complexes such as A Lead chloride is separated from the other two chlorides by heating with water. The PbCl, dissolves in hot water by the reverse of Reaction 2: Phats) â Pb2+ (aq) + 2 cr(aq) Once Pb2+ has been put into solution, we can check for its presence by adding a solution of Koro, The chro- mate ion, Cro.. gives a yellow precipitate with Pb yellow The other two insoluble chlorides, AgCI and Hg Cl, can be separated by adding aqueous ammonia. Silver chloride dissolves, forming the complex ion Ag(NH): AgCl(s) + 2 NHfaq) â Agt NH),'(aq) + Cr(aq) Ammonia also reacts with Hg,Cl, via a rather unusual oxidation-reduct finely divided metallic mercury, which is black, and a compound of formula HgNH,CI, which is white: ion reaction. The products include HE:Cl2(s) + 2 NH, (aq) â Hg(1) + HgNH,CIS) + NH,' (aq) + Cr(aq) black white white As this reaction occurs, the solid appears to change color, from white to black or gray