What is the pH of a neutral solution at 25°C?

A neutral solution at 25°C has a pH of 7.0. This value signifies a balance between hydrogen ions (H⁺) and hydroxide ions (OH⁻) in the solution. At 25°C, the concentration of H⁺ ions and OH⁻ ions in pure water is both 1.0 x 10⁻⁷ M, leading to a neutral condition where the pH is derived from the negative logarithm of the hydrogen ion concentration:

pH = -log[H⁺]

Substituting in the concentration yields:

pH = -log(1.0 x 10⁻⁷) = 7.0.

This pH 7.0 serves as the reference point for acidity and alkalinity, with values below 7 indicating acidity and values above 7 indicating alkalinity. The pH scale itself is logarithmic, which implies that each whole number change in pH represents a tenfold change in hydrogen ion concentration. As such, a pH of 7.0 is crucial for many biological and chemical processes, with deviations from this value significantly impacting reaction dynamics and the stability of various compounds.