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Out-of-class Assignment #5

  1. Is it possible to find a pH range (limit this to integer values) in which it is possible to have 99.9% of Fe(III) complexed with the ligand DCTA (see Table 12.1 on our equilibrium constant handout) but 99.9% of Ba(II) in its  uncomplexed form?  The initial concentrations are 0.020 M Fe(III), 0.020 M Ba(II), and 0.10 M total DCTA.
  2. Is 99.99% of the Pb(II) complexed with DTPA if 30 ml of0.05 M Pb(II) is mixed with 30 ml of 0.05 M total DTPA and the final solution is buffered at pH 4?
  3. A common method of analysis is to measure the fluorescence of a substance.The compound phthalic (2-) acid can be measured this way but the fluorescence of phthalic acid (H2P), the monophthalate ion (HP-) and phthalate (P2-) are distinctly different.  For analytical purposes, the monophthalate ion is the most useful.  Is there a particular pH at which you could buffer the solution and be assured that at least 99.9% of the phthalic acid is in the form of the monophthalate ion?