Chemistry Regents Practice Test

The pH scale is specifically designed to measure the concentration of hydrogen ions (H⁺) in a solution. A lower pH value corresponds to a higher concentration of hydrogen ions, which indicates a more acidic solution, while a higher pH value reflects a lower concentration of hydrogen ions and a more basic or alkaline solution.

The formula used to calculate pH is pH = -log[H⁺], where [H⁺] is the molarity of hydrogen ions in the solution. This logarithmic relationship means that each whole number change on the pH scale represents a tenfold change in hydrogen ion concentration. For instance, a solution with a pH of 3 has ten times more hydrogen ions than one with a pH of 4.

Understanding that pH measures hydrogen ion concentration helps in various applications, including in biology, where enzyme activity can be dependent on the pH of the environment, and in environmental science, where the pH of water bodies can affect aquatic life.

The other choices are related concepts but do not define what pH measures. For instance, total concentration of all ions could refer to a broader category, hydroxide ions specifically measure the basicity aspect, and the acidity or basicity of a