Acids and Bases (Encyclopedia of Science)
Acids and bases are chemical compounds that have distinctive properties in water solution. The sour taste of a lemon, lime, or grapefruit, for example, is caused by citric acid. The slippery feel of ammonia, a common base, is characteristic of all bases. One of the most interesting properties of acids and bases is the way they react with indicators. An indicator is a material that changes color in the presence of an acid or a base. For instance, the hydrangea flower can be either pink or blue, depending on the amount of acid or base present in the soil in which it is planted.
Acids and bases have been known since prehistoric times. Vinegar, for example, is a water solution of acetic acid that has been used for centuries. The first modern definitions for acids and bases were suggested by Swedish chemist Svante Arrhenius (1859927). Arrhenius proposed that acids be defined as chemicals that produce positively charged hydrogen ions, H+, in water. By comparison, he suggested that bases are compounds that produce negatively charged hydroxide ions, OH/sup>, in water. Acids and bases react with each other in a reaction called neutralization. In a neutralization reaction, the hydrogen ion from an acid and the hydroxide ion from a base react to form a molecule of water:
H+ + OH/sup> H2O
Other definitions of...
(The entire section is 928 words.)
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