Lead Assay Titration with Ammonium Molybdate

Lead Assay Titration with Ammonium Molybdate

  • 1 gram of sample is decomposed with longer appear 10 cc’s of H2SO4 is added. This solution is evaporated to dryness and allowed to cool.
  • Add 10 cc’s H2SO4 and 65 to 70 cc’s H2O and heat to boiling to dissolve all soluble salts. Do not boil!
  • Filter by decantation and wash three times with cold water using as small amount of water as possible, as lead sulphate is slightly soluble in hot water.
  • Place filter paper in a beaker breaking it up into small pieces.
  • Then add the ammonium acetate solution.
    A large excess of ammonium acetate as well as too small an amount, cause drastic results (see note).
  • Dilute up to 150 cc’s with boiling water.
  • Boil 20 minutes and titrate with ammonium molybdate solution, using tannic acid as outside indicator.

Preparation Of Reagents:

  • 3 grams of ammonium molybdate diluted to 1 litre of cc solution is equivalent to .005 grams of lead.
  • Tannic Acid:
    1 gram to 30 cc’s of water. Ammonium acetate to 65% solution.