# In-class Problem Set #1

*Problem #1*

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

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

*Problem #2*

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

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

*Problem #3*

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

- 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)
- Identify a compound that is a weak acid
- Identify whether an anion is an anion of a strong acid
- Identify whether a cation is a cation of a strong base
- 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
- 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:

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