ANALYSIS OF THE GROUP I METALS

(Hg, Pb, Ag)

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.

GROUP I FLOW SHEET

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