In this lesson we have seen that the behavior of acids and bases is characterized by reactions whose position of equilibrium is related to the strength of the acids and bases involved. There is, in fact, a predictable balance between the strength of an acid and its conjugate base that is reflected in the position of equilibrium.
We can express the strength of an acid (or a base) mathematically using the equilibrium constant expression and the value of the Ka (or Kb) that applies. This allows us to calculation the pH given the strength and concentration of acid or base present in solution.
The dynamic equilibrium between the concentration of acid and conjugate base is governed also by Le Chatelier's principle, which allows us to predict the response of a system to changes that are imposed from the outside.
We saw that the conjugate base of an acid can be a component of a salt which, when it dissolves in solution, can cause the solution to turn basic. Similarly, salts also may contain the conjugate acid of a base, which can turn solutions of the salt acidic.
Finally, we explored the function of buffer solutions, solutions that contain both a weak acid and its (weak) conjugate base. With both species present, the pH of the solution tends to stay constant as the acid neutralizes added base while the base neutralizes added acid. We learned a simple equation that allows us to predict the pH of a buffer solution based on the Ka of the acid and the relative concentrations of the acid and its conjugate base.
Be sure to turn in the lab and the problem set for this lesson and to try the self quiz before you come in to take the quiz. As usual, you'll find the answers to the self quiz by clicking on the link at the top, left-hand side of this page. The Answer page contains answers to selected exercises and problems from your workbook. Remember, you may turn in a group lab report for this lesson if you wish. The graph for the lab report should be done on the computer, not by hand (it is too difficult to be precise enough with a hand-drawn graph). If you need help doing the graph, the lab instructors can assist you.