Skip to main content
Chemistry LibreTexts

In-class Problem Set #3

Problem #1

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

  1. Write the appropriate reactions and equilibrium constant expressions for a solution of a polyprotic acid
  2. Write an expression for the concentration of H3O+ in terms of other species produced by the dissociation of the acid
  3. Explain why the first reaction in the sequence is much more significant than any subsequent reactions in the stepwise dissociation of a solution of a polyprotic acid
  4. Solve for the pH of the solution of a polyprotic acid

Problem #2

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

  1. Write the appropriate reactions and equilibrium constant expressions for a solution of a polybasic compound
  2. Determine the Kb values for each reaction in the series
  3. Explain why the first reaction in the sequence is much more significant than any subsequent reactions in the stepwise reaction of a polybasic compound
  4. Solve for the pH of the solution of a polybasic compound
  5. Name polyprotic acids as well as the other species in the series of reactions that represent the dissociation of a polyprotic acid.

Problem #3

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

  1. Determine the concentration of species in a solution of a polybasic compound that has a quantity of strong acid added to it
  2. Determine the concentration of species in a solution of a polyprotic acid that has a quantity of strong base added to it
  3. Explain why a polyprotic system can be used to prepare more than one buffer, each of which is centered around the different pKa values for the polyprotic acid
  4. Solve for the pH of the solution prepared by adding a strong acid to a polybasic compound or strong base to a polyprotic acid

Problem #4

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

  1. Determine the redistribution of species that occurs when phosphoric acid is mixed with sodium phosphate
  2. Show that the redistribution of species that occurs in learning objective 1 usually leads to the formation of a buffer
  3. Solve for the pH when two or more species in a polyprotic acid system are mixed together in solution

Problem #5

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

  1. Write an expression for the concentration of H3O+ in terms of other species of a polyprotic acid system when the initial solution is prepared using on an intermediate species
  2. Derive an expression for H3O+ using the appropriate Ka expressions and the expression written in learning objective #1.
  3. Show that, in most circumstances, the pH of a solution prepared using only an intermediate species is the average of the two appropriate pKa values