What does pH measure?

The pH of a solution specifically measures the concentration of hydrogen ions (H⁺) in that solution. The pH scale, which ranges from 0 to 14, is logarithmic, meaning that each whole number change in pH represents a tenfold change in hydrogen ion concentration. A lower pH means a higher concentration of hydrogen ions and indicates a more acidic solution, while a higher pH indicates a lower concentration of hydrogen ions and a more basic (or alkaline) solution. Understanding this concept is crucial for analyzing the acidity or basicity of various solutions in chemical reactions and processes.

Other options touch on related concepts but do not define what pH measures. Temperature is a physical property that can affect chemical behavior but is unrelated to pH. The concentration of hydroxide ions relates to the basicity of a solution and can be derived from pH, but it does not directly define pH. Total ionic strength pertains to the total concentration of ions in a solution and is important for understanding solution behavior, but it is not what pH quantifies. Thus, the correct interpretation of pH as a measure of hydrogen ion concentration is essential to grasp the core principles behind acid-base chemistry.