How is pKw related to pH and pOH?

The relationship between pKw, pH, and pOH is grounded in the concept of water's dissociation and the properties of logarithms. In pure water at 25°C, the concentration of hydrogen ions [H⁺] and hydroxide ions [OH⁻] are equal, and both can be used to define pH and pOH.

The formula for pKw is derived from the ion product of water (Kw), which is the product of the concentrations of hydrogen and hydroxide ions:

Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C.

Taking the negative logarithm of both sides gives:

pKw = -log(Kw) = -log([H⁺][OH⁻]) = -log[H⁺] - log[OH⁻],

which simplifies to:

pKw = pH + pOH.

This equation indicates that the sum of pH and pOH will always equal pKw at a given temperature, which is 14 at 25°C. Thus, the correct answer indicates that pKw can be expressed as the sum of pH and pOH, reflecting the fundamental relationship in