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Acid Base Theories: Svante Arrhenius.

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Acid Base Theories: Svante Arrhenius I. Introduction Svante Arrhenius was one of the towering giants of chemistry in the years surrounding the turn of the century. His most important contribution to chemistry was also his first - the idea of electrolytic dissociation. This idea first published in 1883 and in refined form in 1887, was the mainstay of his doctoral dissertation. It was the source of much hurt in his life. The basic idea is that certain substances remain ionised in solution all the time. Today, everyone accepts this without question, but it was the subject of much dissention and disagreement in 1884, when a twenty-five year old Arrhenius presented and defended his dissertation. He was bitterly disappointed when the dissertation was awarded a fourth class (non since laude approbatur - approved not without praise) ...read more.


to the solution. Base - any substance, which delivers hydroxide ion (OH�) to the solution. Here is a generic acid dissociating, according to Arrhenius: HA H+ + A� This would be a generic base: XOH X+ + OH� When acids and bases react according to this theory, they neutralize each other, forming water and a salt: HA + XOH H2O + XA Keeping in mind that the acid, the base and the salt all ionise, we can write this: H+ + A� + X+ + OH� H2O + X+ + A� Finally, we can drop all spectator ions, to get this: H+ + OH� H2O These ideas covered all of the known acids at the time (the usual suspects like hydrochloric acid, acetic acid, and so on) ...read more.


3) The need for hydroxide as the base led Arrhenius to propose the formula NH4OH as the formula for ammonia in water. This led to the misconception that NH4OH is the actual base, not NH3. In fact, by 1896, several years before Arrhenius announced his theory, it had been recognized that characteristic base properties where just as evident in such solvents as aniline, where no hydroxide ions were possible. 4) H+, a bare proton, does not exist for very long in water. The proton affinity of H2O is about 799 kJ/mol. Consequently, this reaction: H2O + H+ H3O+ happens to a very great degree. The "concentration" of free protons in water has been estimated to be 10�130 M. The Arrhenius theory of acids and bases will be fully supplanted by the theory proposed independently by Johannes Br�nsted and Thomas Lowry in 1923. ...read more.

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