Buffer Capacity

Abstract

Buffer capacity quantifies the ability of a solution to resist changes in pH by either absorbing or desorbing H+ and OH- ions. When an acid or base is added to a buffer system, the effect on pH change can be large or small, depending on both the initial pH and the capacity of the buffer to resist change in pH. Buffer capacity (β) is defined as the moles of an acid or base necessary to change the pH of a solution by 1, divided by the pH change and the volume of buffer in liters; it is a unitless number. A buffer resists changes in pH due to the addition of an acid or base though consumption of the buffer. As long as the buffer has not been completely reacted, the pH will not change drastically. The pH change will increase (or decrease) more drastically as the buffer is depleted: it becomes less resistant to change. Calculating Buffer Capacity Buffer capacity is determined through a titration, a technique in which a known volume and concentration of a base or acid is added to the analyte of unknown concentration (Figure 2). In the analysis performed by the Chemistry 221 class, a PASCO Xplorer GLX data logger with a pH electrode was used to monitor the change in pH. When determining buffer capacity through a titration experiment, the flat region of the titration curve before the equivalence point is the buffer region (Figure 3). Past the buffer region, pH changes drastically near the equivalence point. In a laboratory environment, a buffer solution can be created by mixing a weak acid with its conjugate base. The ions naturally present in rivers are buffering components that allow the pH of the water to remain stable over time. Buffer capacity of river water is very important, usually necessitating narrow pH ranges that are critical to the survival of most organisms. If the buffer capacity of river water is too small or the pH of the water is outside its buffer range, it can be lethal to the river’s ecosystem. According to Van Vooren, buffer capacity can be used in the analysis of water samples in order to determine the water quality (2001). Summary Buffer capacity is a quantitative measure of resistance to pH change upon the addition of H+ or OH- ions. It is important for river water to maintain a stable pH such that the local ecosystems are preserved in order to keep Columbus flourishing.