pH (hydrogen ion concentration)

pH is an indicator that shows the degree of acidity or alkalinity of an aqueous solution, defined as the logarithm of the reciprocal of the hydrogen ion concentration (or hydrogen ion activity), and is also referred to as the hydrogen index. The pH of pure water is neutral and is approximately pH 7; values higher than this indicate alkalinity, while lower values indicate acidity. The reactions of substances in water can change significantly depending on the pH, making it an important indicator of the chemical properties of water. For this reason, pH is widely measured not only in environmental monitoring but also in industrial applications.