Wrap-Up

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 K_a (or K_b) that applies. This allows us to calculate the pH given the strength and concentration of acid or base present in solution.

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. Knowledge of these hydrolysis reactions can be used to write equations for them, and to predict whether a given salt solution will be acidic, basic, or neutral.

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 K_a of the acid and the relative concentrations of the acid and its conjugate base.