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Chemistry LibreTexts

In-class Problem Set #4

Problem #1

After completing this problem, the student will be able to:

  1. Write the reaction of a metal ion and ligand to form water-soluble metal complexes.
  2. Write the expression for KF
  3. Solve for the concentration of free metal ion, unbound ligand, and metal complex if given the initial concentration of metal and ligand
  4. Describe what is meant by a chelating ligand
  5. Rationalize why entropy effects account in large part for the high formation constants of chelating ligands with metal ions
  6. Describe broad families of ligands (anionic species and nitrogen bases)
  7. Write both the neutral and zwitterionic structurew of a ligand such as EDTA

Problem #2

After completing this problem, the student will be able to:

  1. Write and evaluate the expression for the fraction of the ligand (weak base) that exists in the fully deprotonated form.
  2. Write and evaluate the expression for the fraction of any other form of the ligand (any species in a series of acid or base reactions)
  3. Show that these fractions are only dependent on the pH and not the total concentration of the ligand
  4. Explain why the α-value for the fully deprotonated ligand is high at basic pH and low at acidic pH.
  5. Explain why the α-value for the fully protonated ligand is high at acidic pH and low at basic pH.
  6. Explain why the α-value for an intermediate species is low at highly acidic or basic pH values and maximized at an intermediate pH value.
  7. Graph the α-values for all of the species of a polyprotic acid.
  8. Evaluate the conditional constant at any pH.
  9. Use the conditional constant to determine the final concentrations of unbound metal ion, metal complex, and all forms of the unbound ligand if given the initial concentration of metal and ligand.
  10. Explain why the formation of a metal complex with a ligand that is a weak base is more favorable at basic pH.
  11. Write and evaluate the expression for the fraction of a metal that exists in solution as its unbound metal ion when in the presence of a competing ligand.
  12. Show that this fraction only depends on the concentration of the competing ligand, provided complexation does not lower its value appreciably.
  13. Write and evaluate the fraction of all other metal complexes with the competing ligand.
  14. Incorporate the α-value for the unbound metal ion into the KF expression and determine the value of the conditional constant.
  15. Use the conditional constant to determine the final concentrations of unbound metal ion, desired metal complex, and all forms of the unbound ligand and other metal complexes if given the initial concentration of metal and ligand.