Advanced Placement (AP) Chemistry Practice Exam

The value 1.0 x 10^-14 is significant in chemistry because it represents the ion product of water, also known as the dissociation constant of water at 25°C. This constant indicates the concentration of hydrogen ions [(H⁺)] and hydroxide ions [OH⁻] in pure water at this temperature, where the relationship can be expressed as:

\[ K_w = [H^+][OH^-] = 1.0 \times 10^{-14} \]

This value plays a crucial role in understanding acid-base chemistry, as it establishes the basis for the pH scale, with the pH of pure water at 25°C being 7 (indicating neutrality), where [H⁺] = [OH⁻] = 1.0 x 10^-7 M.

In contrast, other options carry different meanings. The equilibrium constant for a weak acid pertains to specific acid dissociation reactions, the indication of pH level relates more directly to the logarithmic scale derived from hydrogen ion concentration, and the solubility product constant applies specifically to the equilibrium of saturated solutions of salts, none of which relate directly to this fundamental property of water at room temperature.