VERIFICATION OF THE HENDERSON-HASSELBALCH EQUATION R. QUENTIN BLACKWELL and LEONARD S. FOSDICK Northwestern University Dental School, Chicago, Illinois
THEaccurate conception of buffers and buffer action is extremely important in a number of phases of biochemistry. We have found that many students coming into our biochemistry classes have a rather sketchy knowledge of the subject. This is particularly true with respect t o the significanceof theHenderson-Hasselbalch equation and its relationship to buffer action. Accordingly me use a simple experiment to aid in iucreasing the understanding of the student on these subjects. The experiment is run as a laboratory demonstration with a considerable amount of discussion accompanying the demonstration; it is preceded by a discussion of buffers, and in addition problems concerning buffers are solved by the students. Since the experiment involves use of the pH meter the schedules are arranged in such a way that the pH meter is discussed and its use demonstrated in the laboratory period preceding the one in which the buffer experiment is presented. Solution
Vol. of 0.1 M acetate
Vol. of 0.1 M acetic acid
Cone. of acetale Isail l
The experiment itself is simply a comparison of the actual pH of buffer solutions with the theoretical pH as predicted by the Henderson-Hasselbalch equation. For simplicity 0.1 M solutions of acetic acid and sodium acetate are used, and the pH's of various mixtures of the two solutions are measured. The data obtained in the demonstration are recorded by the students in a table supplied in their mimeographed laboratory manual. A reproduction of the tahle appears below. The necessary calculations are made by the students to fill in the empty columns in the tahle; when the table is filled it provides a comparison of calculated and observed pH values for the various mixtures of salt and acid. The agreement is usually within approximately 0.1 pH unit, which illustrates the validity of the equation. Following the demonstration a short discussion emphasizes the mechanism of buffer action, and numerous examples are cited in which buffer action is extremely important in biochemistry. Cane. of aeelie acid lacidl
[Salll IAcidl
log [Salt] [Acid1
Calculated
Observed
UH
OH
