Acids & Bases unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Titration curve of a weak acid
Structure and acid strength
pH, pOH and their relationship
Henderson-Hasselbalch equation
Choosing an indicator
Salt hydrolysis
Diluting a buffer
Why pH = pKa at half-equivalence
Autoionization of water
Buffer
Amphoteric species
Strong vs weak acids
Short answer 1. Define or explain: Equivalence point pH
3 ptsShort answer 2. Define or explain: Percent ionization
3 ptsShort answer 3. Define or explain: Relationship of Ka and Kb
3 ptsShort answer 4. Define or explain: Titration curve features to label
3 ptsFree response
10 ptsA student prepares a buffer by dissolving 0.100 mol of sodium acetate, NaCH₃COO, in 500. mL of 0.200 M acetic acid, CH₃COOH (Ka = 1.8 × 10⁻⁵). Assume no volume change on dissolving.
(a) Write the equation for the ionization of acetic acid in water.
(b) Calculate the concentration of acetate ion in the buffer.
(c) Calculate the pH of the buffer.
(d) Calculate the pH after 0.0100 mol of solid NaOH is added to the buffer, assuming no volume change.
(e) Explain, using your answers to (c) and (d), why the solution is described as a buffer.
(f) Calculate the pH that would result if the same 0.0100 mol of NaOH were added to 500. mL of pure water instead.
(g) Describe the ratio of acid to conjugate base that gives a buffer its maximum capacity, and justify your answer.
(h) Identify the pH at which this buffer system is most effective, and justify your identification.
(i) Predict the effect on the buffer’s pH of diluting it with an equal volume of water, and justify your prediction.
(j) Describe one change the student could make to increase the buffer capacity while keeping the pH the same.