The pH scale, which ranges from 0 to 14, indicates how acidic or alkaline a material is. The scale is based on the concentration of hydrogen, H, and hydroxide, or OH, ions. The lower the number on the pH scale, the greater the concentration of hydrogen ions and the greater the material's acidity. The higher the number assigned on the pH scale, the greater the concentration of hydroxide ions and the more basic, or alkaline, the material.
A Logarithmic Scale
If something has a pH of 7.0, it is neutral. Milk usually has a pH around 7.0. A pH below 7.0 indicates acidity, while a pH above 7.0 is basic, or alkaline. Each pH value is 10 times more or less acidic or alkaline than the number next to it on the pH scale. For example, a pH of 3.0 is 10 times more acidic than a pH of 4.0, while a pH of 11 is 10 times less alkaline than a pH of 12 and 100 times less alkaline than a pH of 13. Materials that are very acidic or basic are known as reactive and can cause severe burns. Examples of reactive materials include automobile battery acid and lye, sometimes found in household drain cleaner.