Positive-negative acid-base theory

The Usanovich theory is the most general of all acid-base theories. According to Usanovich (1939) any process leading to the formation of a salt is an acid-base reaction. The so-called positive-negative definition of Usanovich runs as follows. 

This ability to interact strongly with positively and negatively charged ions is consistent with water s nnique amphoteric (acid-base) properties, and is why it is fundamental to the Bronsted acid-base theory (equations 4 and 5). 

Another acid-base theory that is useful for solvents other than water was postulated by American chemist Fdward Franklin in 1905. It makes use of the autoionization of solvents, and defines an acid as a solute that produces the positively charged species of the solvent and a base as a solute that produces the negatively charged species of the solvent. In the case of the autoionization of water (equation 18) HjO is the acid and OH is the base. For the nonaqueous solvent, liquid ammonia, the autoionization gives... 

The Electrolytic Dissociation Theory. —From his studies of the conductances of aqueous solutions of acids and their chemical activity, Arrhenius (1883) concluded that an electrolytic solution contained two kinds of solute molecules these were supposed to be active molecules, responsible for electrical conduction and chemical action, and inactive molecules, respectively. It was believed that when an acid, base or salt was dissolved in water a considerable portion, consisting of the so-called active molecules, was spontaneously split up, or dissociated, into positive and negative ions it was suggested that these ions are free to move independently and are directed towards the appropriate electrodes under the influence of an electric field. The proportion of active, or dissociated, molecules to the total number of molecules, later called the degree of dissociation, was considered to vary with the concentration of the electrolyte, and to be equal to unity in dilute solutions. 

Before leaving this subject, some other theories of the decomposition of salt solutions by an electric current may be mentioned. Riffault and Chompre supposed that two simultaneous currents caused decompositions throughout their whole course, producing separation of the elements there and not only at the poles. The negative current carried acids etc. to the positive pole, and the positive current carried bases to the negative pole. The currents were supposed to be more powerful nearer their respective poles, and the positive current superior in power to the negative current, nitrate of soda being decomposed by the former but not by the latter. 

Davy s move to the Royal Institution meant that he had to abandon his electrochemical researches for a while. In 1803 Berzelius and Wilhelm Hisinger (1766-1852) found that when an electric current was passed through solutions of various salts, acids were found at the positive pole and bases at the negative. This observation was probably important in leading Berzelius to the dualistic theory (see below). 

Svante Arrhenius (1859-1927) was a Swedish physical chemist who was awarded the Nobel Prize in Chemistry in 1903 for his work on ionic solutions. His theory of acids and bases defined acids as substances that produce hydrogen ions in solution (as the only positive ions) and bases as substances that produce hydroxide ions (as the only negative ions). In addition he explored the relationship between the rate of a chemical reaction and temperature. The equation which bears his name was originally proposed by the Dutch chemist J.H. varit Hoff, but it was Arrhenius who provided a physical interpretation and justification for it When the temperature increases, the rate of a chemical reaction increases very rapidly. It has been found that for many reactions, the initial rate and the rate constant. 

Electrolytic Dissociation or Ionization Theory n When an acid, base or salt is dissolved in water or any other dissociating solvent, a part or all of the molecules of the dissolved substance are broken up into parts called ions, some of which are charged with positive electricity and are called cations, and an equivalent number of which are charged with negative electricity and are called anions. 

Arrhenius, Svante August (1859-1927) A Swedish physicist and chemist who did fundamental work on physical chemistry. He worked with van t Hoff in Amsterdam and proposed a theory of activated molecules and established a coimecdon between rate of reaction and absolute temperature. He also developed a theory for electrolytic dissociation based on van t Hoff s results and stated that any acid, base, or salt dissolved in water is partly split up into positively and negatively charged ions, and that they move in opposite directions on electrolysis. He was awarded a Nobel Prize for Chemistry in 1903. 

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