Making pH Tangible.

The concept of pH is an important one for our students. All of our experiments depend upon pH, and nearly every process in living cells depends upon the maintenance of a proper pH level, as enzymes will generally only function within a narrow pH range. Since the synthesis of adenosine triphosphate in living cells depends upon the creation and maintenance of a pH gradient, it is worth noting that nearly all of the energy used by all living systems on this planet comes from pH gradients. Many students have a difficult time understanding the concept of pH, as it is somewhat abstract, and mathematical on a logarithmic scale. We present here a simple set of experiments to give students practical, hands-on experience with pH. The labs also touch on the mathematics by demonstrating the logarithmic nature of the scale. These experiments are appropriate for high school biology or introductory college-level biology labs. pH is the measure of the hydrogen ion (H+) concentration of an aqueous solution. In our experiments, as well as within our bodies, we keep the concentration of H+ ions constant by using buffers, chemicals that will compensate for changes in this ion by absorbing excess ions as the pH goes down, or freeing them as the pH goes up. For instance, our blood must maintain a pH level of 7.35-7.45. A slight change can cause severe illness and even death. Therefore blood must have a system with which to control the level of pH. One such system is a bicarbonate buffer system, which consists of carbonic acid, a weak acid, and sodium bicarbonate, its complementary weak base.