What equation represents the relationship between pH and pOH?

The correct equation that represents the relationship between pH and pOH is that the sum of pH and pOH equals 14 at 25°C. This relationship emerges from the concept of water's autoionization, where water dissociates into hydrogen ions (H⁺) and hydroxide ions (OH⁻).

At room temperature, the product of the concentrations of these ions is always constant, represented by the ion product of water (Kw = [H⁺][OH⁻] = 1 x 10⁻¹⁴), leading to the establishment of the pH and pOH scale. Specifically, pH is defined as the negative logarithm of the hydrogen ion concentration, and pOH is the negative logarithm of the hydroxide ion concentration. The relationship pH + pOH = 14 reflects this balance, whereby as one increases, the other decreases, maintaining the overall sum at 14.

This foundational concept is critical in understanding acid-base chemistry, buffering systems, and the behavior of substances in aqueous solutions, especially in biological systems where pH plays a significant role in enzyme function and biochemical pathways.