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Litmus paper is a neutral paper made of wood cellulose infused with a water-soluble dye made from specific lichens. Lichens are small symbiotic organisms made up of a fungus and an alga living as one organism. They grow on rocks and trees and have been used for generations to dye cloth. Litmus paper can be either red or blue and tests for acids and bases.
To understand acids, it is necessary to understand the definition of an ion. An ion is an atom with an electrical charge; this means it is reactive with other substances. Acidic ions are positively charged, which means they have an extra proton that tries to combine with a negatively charged ion to stabilize itself. Acids taste sour and have strong reactions to metals. In addition, strong acids can burn you.
Bases, or alkaline substances, have negatively charged ions and thus accept protons in the effort to stabilize themselves. When
acids and bases combine, the resulting matter is known as a neutral salt. Bases taste bitter and feel slippery; strong ones can burn skin.
The pH scale is used to indicate the acidity or alkalinity of a substance according to the degree of available ions. The pH scale is from zero to 14. Zero is the most acidic measurement and 14 is the most alkaline or basic. Neutral substances are designated as seven. PH is important because most life forms have a limited range of pH in which they are viable.
Acid turns blue litmus paper red. Bases turn red litmus paper blue. This is true because the original color of litmus is blue. During manufacture, the red litmus paper is mixed with an acid to turn it red. When red litmus comes into contact with a base, it returns to its original blue shade. Examples of common basic substances include sodium bicarbonate--or baking soda--human blood, milk of magnesia, ammonia, lime and lye.