Definitions
A strong base is a base which hydrolyzes completely, raising the pH of the solution toward 14. Concentrated bases, like concentrated acids, attack living tissue and cause serious burns. The reaction of bases upon contact with skin is different from that of acids. So while either may be quite destructive, strong acids are called corrosive, and strong bases are referred to as caustic. Superbases are a class of especially basic compounds and non-nucleophilic bases are a special class of strong bases with poor nucleophilicity. Bases may also be weak bases such as ammonia, which is used for cleaning. Arrhenius bases are water-soluble and these solutions always have a pH greater than 7 at standard conditions. An alkali is a special example of a base, where in an aqueous environment, hydroxide ions are donated. There are other more generalized and advanced definitions of acids and bases.
The notion of a base as a concept in chemistry was first introduced by the French chemist Guillaume François Rouelle in 1754. He noted that acids, which in those days were mostly volatile liquids (like acetic acid), turned into solid salts only when combined with specific substances. Rouelle considered that such a substance serves as a base for the salt, giving the salt a "concrete or solid form".
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