What is Acidity?
Acidic and basic are two extremes that describe chemicals, just like hot and cold are two extremes that
describe temperature. Mixing acids and bases can cancel out their extreme effects, much like mixing
hot and cold water can even out the water temperature. A substance that is neither acidic nor basic is
neutral. The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14.
A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic. Each whole pH value below
7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH
5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each
of which is ten times more alkaline (another way to say basic) than the next lower whole value. For example, pH 10 is ten
times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than
Pure water is neutral. But when chemicals are mixed with water, the mixture can become either acidic or
basic. Examples of acidic substances are vinegar and lemon juice. Laundry detergents and ammonia are
examples of basic substances. Chemicals that are very basic or very acidic are reactive. These chemicals
can cause severe burns. Automobile battery acid is an acidic chemical that is reactive. Automobile
batteries contain a stronger form of some of the same acid that is in acid rain. Household drain cleaners
often contain lye, a very alkaline chemical that is reactive.
EPA page: acidity