PROCEDURE 1: To 10 drops of the solution to be analyzed, add enough water to make a total volume of 1 ml. Add 2-5 drops of 6M hydrochloric acid (HCl) to this solution. Separate the precipitate by centrifugation. If your sample is a general unknown reserve the centrifugate (solution) for the analysis of groups II-V. If your sample is a group I known or unknown only, test the solution for lead as directed in procedure 2. Treat the precipitate according to procedure 2.
PROCEDURE 2: Precipitate from (1): HgCl2,AgCl, and PbCl2. Extract the precipitate twice with 10 drops of hot water to dissolve the lead chloride (PbCl2). Reserve the residue for procedure 3. Add 2 drops of 1M potassium chromate (K2CrO4) to the solution (hot water extract). A yellow precipitate of lead chromate (PbCrO4) confirms the presence of lead.
PROCEDURE 3: Residue from (2): HgCl2 and AgCl. Extract the residue twice with 5 drops of 4M aqueous ammonia (NH4OH). A black or gray residue confirms the presence of the mercury ion. Reserve the aq. ammonia extract for procedure 4.
PROCEDURE 4: Solution from (3): AgCl. Add 4 M nitric acid (HNO3) until the solution is acid to litmus paper. A white precipitate (or cloudiness) of silver chloride (AgCl) confirms the presence of silver.
Hg++ + HCl HgCl2 hot H2O HgCl2 + NH4OH Hg (black)
Ag+ + HCl AgCl hot H2O AgCl + HNO3 AgCl (white)
Pb++ + HCl PbCl2 hot H2O Pb++ + K2CrO4 PbCrO4 (yellow)
Return to The Third Millennium Online