pH - Value

The pH value is a dimensionless measure of the acid, neutral or basic character of an aqueous solution. It measures the activity of hydrogen ions on a logarithmic scale from 0 to 14. A pH value of 7 is considered neutral, representing the pH of distilled pure water without dissolved CO2. Values smaller than 7 are acidic, while values greater than 7 are alkaline.

For drinking water, authorities stipulate a pH range of not less than 6.5 and not more than 9.5. Waterworks often add lime slurry to raw water to achieve a pH close to neutral.

Examples of pH values include: vinegar (2.0), sulfuric acid (2.75), acid rain (5.0), human urine (6.0), milk (6.4), pure water (7.0), blood (7.4), soap (10.0), bleach (12.5), and caustic soda (14.0). These are average values that may vary; for instance, human urine pH depends on diet, medications, and health conditions, ranging from 5.0 to 8.5.