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Jennifer KingPeriod 3April 28 2001 Acids and Bases Modern understanding of acids and bases began with the discovery in 1834 by the English physicist Michael Faraday that acids bases and salts are electrolytes That is when they are dissolved in water they produce a solution that contains charged particles or ions and can conduct an electric current ionization In 1884 the Swedish chemist Svante Arrhenius and later Wilhelm Ostwald a German chemist proposed that an acid be defined as a hydrogen-containing compound that when dissolved in water produces a concentration of hydrogen ions or protons greater than that of pure water Similarly Arrhenius proposed that a base be defined as a substance that when dissolved in water produces an excess of hydroxyl ions OH- A number of criticisms of the Arrhenius-Ostwald theory have been made First acids are restricted to hydrogen-containing species and bases to hydroxyl-containing species Second the theory app lies to aqueous solutions exclusively whereas many acid-base reactions are known to take placein the absence of water A more satisfactory theory was proposed in 1923 by the Danish chemist Johannes Brnsted and independently by Thomas Lowry a British chemist Their theory states that an acid is a proton hydrogen ion H donor and a base a proton acceptor Although the acid must still contain hydrogen the Brnsted-Lowry theory does not require an aqueous medium For example liquid ammonia which acts as a base in aqueous solution can act as an acid in the absence of water by transferring a proton to a base and forming the amide anion negative ion NH2- The Brnsted-Lowry definition of acids and bases also explains why a strong acid displaces a weak acid from its compounds and likewise for strong and weak bases Here acid-base reactions are viewed as a competition for protons In terms of a general chemical equation the reaction of Acid 1 with Base 2 res ults
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