pHskala

pHskala, commonly referred to as the pH scale, is a measure of how acidic or basic (alkaline) an aqueous solution is. It is typically shown on a range from 0 to 14 at standard room temperature, with 7 representing neutrality. Values below 7 indicate acidity, while values above 7 indicate basicity. The scale is logarithmic, so each unit represents a tenfold change in hydrogen ion activity.

The pH of a solution is defined by the equation pH = -log10(aH+), where aH+ is the activity of hydrogen ions in the solution. Activity, rather than simple concentration, accounts for interactions between ions and the solvent. Temperature affects the neutral point and the accessible range; at higher temperatures the precise 0–14 range may not apply as strictly.

In practice, pH is measured with electronic pH meters, pH indicators, or colorimetric test papers. Meters require regular calibration with standard buffer solutions to ensure accuracy. The pH scale is widely used across science and industry, including chemistry, biology, medicine, environmental science, agriculture, food production, and water treatment, to monitor processes and ensure stability or compatibility of solutions.

Common examples illustrate the scale: pure water at 25°C is neutral with pH around 7; rainwater tends to be slightly acidic due to dissolved carbon dioxide, often near 5.6; strong acids can fall toward 0 and strong bases toward 14. Real-world measurements may extend beyond the traditional 0–14 range in highly concentrated solutions or under nonstandard conditions.