pHvärde

The pH value, or pH, is a measure of how acidic or basic (alkaline) a solution is. It is defined as the negative logarithm of the hydrogen ion activity: pH = -log10(aH+). The conventional scale ranges from 0 to 14 at standard conditions, with 7 considered neutral. Values below 7 indicate acidity, while values above 7 indicate basicity. The pH reflects hydrogen ion activity rather than simple concentration and is influenced by temperature and the presence of other ions.

Measurement methods vary. A pH meter uses a glass electrode to sense H+ activity and requires calibration with known buffer solutions. Indicator methods use color-changing substances or test strips, which provide a quick, semi-quantitative reading. For precision, meters are calibrated regularly and measurements are temperature-compensated.

Important factors include temperature and ionic strength, which can shift the pH value without any chemical change in the solution. In many practical contexts, maintaining a specific pH range is essential, since enzyme activity, chemical stability, and nutrient availability are pH-dependent.

Applications of pH measurement and control span many fields. In biology and medicine, human blood has a narrow safe range around 7.35–7.45. In agriculture and horticulture, soil pH affects nutrient availability. In environmental science, pH influences aquatic ecosystems and soil chemistry. In food and beverage production, wine, dairy, and fermentation processes require controlled pH for flavor and safety. In water treatment and industrial processes, pH adjustment helps prevent corrosion and optimize chemical reactions.