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Chemistry LibreTexts

In-class Problem Set #1

Problem #1

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

  1. Write the reaction of a weak base with water
  2. Identify a chemical that is a weak base
  3. Write the equilibrium constant expression for a reaction of a weak base with water
  4. Use the expression KaKb = Kw to solve for Ka if given Kb (or vice versa)
  5. Prove that KaKb = Kw by writing out and multiplying the appropriate equilibrium constant expressions
  6. Relate and deploy the concept of a conjugate pair (two species that differ by H+)
  7. Recall that the conjugate pair of a weak acid is a weak base (and vice versa)
  8. Rank the relative strengths of bases or acids
  9. Write an expression for the amount of each species present at equilibrium
  10. Recall that Kw = [H3O+][OH-]
  11. Analyze the value of K to determine whether approximations can be made in the calculation.
  12. Predict whether the change in the concentration of base is negligible compared to the initial concentration
  13. Predict whether the amount of hydroxide ion initially in solution will likely be small compared to the amount produced
  14. Make any valid approximations and solve the equilibrium constant expression for concentrations
  15. Validate any approximations using the 5% criteria
  16. Recall typical Ka (or pKa) and Kb (or pKb) values for weak acids and bases, respectively
  17. Recall that pH = -log[H3O+], pKa = -logKa and pKb = -logKb

Problem #2

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

  1. Solve the problem using either the Ka or Kb expression using procedures established in problem 1
  2. Determine whether, for a conjugate pair, the base is a stronger base than the acid is an acid
  3. Recall that a solution that has appreciable concentrations of both members of a conjugate pair is a buffer
  4. Demonstrate qualitatively using appropriate reactions how a buffer can resist changes in pH
  5. Derive the Henderson-Hasselbalch expression for a buffer
  6. Use the Henderson-Hasselbalch expression to explain and show quantitatively that a buffer solution resists changes in pH
  7. Calculate the pH of a buffer using the Henderson-Hasselbalch expression
  8. Relate the criteria that are used in selecting a buffer

Problem #3

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

  1. Relate the common chemical nomenclature that is used to denote cationic and anionic species (Name, using the appropriate suffixes, chemical species that are cationic or anionic)
  2. Identify a compound that is a weak acid
  3. Identify whether an anion is an anion of a strong acid
  4. Identify whether a cation is a cation of a strong base
  5. Recall that the conjugate pair of a strong acid or base is produced to an extent of 100% and exists as a spectator ion in solution
  6. Solve for the pH of a solution of a weak acid 

Problem #4 and 5

After completing these problems, the student will be able to:

  1. Determine that a weak acid and a weak base undergo a neutralization reaction
  2. Write a neutralization reaction
  3. Write the equilibrium constant expression for Kn
  4. Prove that Kn = KaKb/Kw
  5. Determine Kn for a neutralization reaction
  6. Explain why the Kn value for a neutralization reaction will always be large when either the acid or base is strong
  7. Explain when Kn is expected to be large and when Kn may be small for a neutralization reaction
  8. Determine whether a neutralization reaction goes to completion
  9. Be able to solve for the final concentration of all four species present in a neutralization reaction
  10. Explain why a neutralization reaction involving a weak acid and a weak base will often lead to the formation of a buffer. 
  11. Calculate the concentration of species present in a neutralization reaction with a large value of K.
  12. Solve for the final pH of a solution in which a neutralization reaction occurs.