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Gravimetric Analysis (Hunter)

  • Page ID
    281943
  • “Man in the Vat Problem”

    Ramette, R.W. J. Chem. Ed. 1988, 65, 800.

    A workman at a dye factory fell into a vat containing hot, concentrated sulfuric and nitric acid. He dissolved completely! Because nobody witnessed the accident, it was necessary to prove that he fell in so that the man’s wife could collect his insurance money. The man weighed 70 kg, and the human body contains ~6.3 parts per thousand (mg/g) phosphorous. The acid in the vat was analyzed for phosphorous to see whether it contained a dissolved human.

    1. The vat contained 8.00 × 103 L of liquid, and a 100.0 mL sample was analyzed. If the man did fall into the vat, what is the expected quantity of phosphorous in 100 mL?

     

    1. The 100.0 mL sample was treated with a molybdate reagent that precipitated ammonium phosphomolybdate, (NH4)3[P(Mo12O40)] · 12 H2O. This substance was dried at 110˚C to remove waters of hydration and heated to 400˚C until it reached the constant composition P2O5 · 24 MoO3, which weighed 0.3718 g. When a fresh mixture of the same acids (not from the vat) was treated in the same manner, 0.0331 g of P2O5 · 24 MoO3 (FM 3596.46) was produced.
      1. What does this second measurement tell us?

         

         

      2. How much phosphorous was present in the 100 mL sample from the vat? Is this quantity consistent with a dissolved man?

         

         

      3. Does this quantity alone provide enough information for the insurance company to be certain that the man actually dissolved in the vat of acid?

     

     

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