The pH scale is a measure of how acidic or basic (alkaline) a solution is. It ranges from 0 to 14:
- pH < 7 → acidic solution (more hydrogen ions, H⁺)
- pH = 7 → neutral solution (like pure water)
- pH > 7 → basic or alkaline solution (more hydroxide ions, OH⁻)
The pH value is logarithmic, meaning each whole number change represents a 10-fold change in acidity or alkalinity. For example, pH 4 is 10 times more acidic than pH 5.
It’s widely used in chemistry, biology, medicine, and environmental science to monitor acidity levels.