Dissociation Arrhenius hypothesis

All Arrhenius acids contain hydrogen i n their formula and produce hydronium ion (H30 ) in aqueous solution. All Arrhenius bases produce hydroxide ion (OH ) in aqueous solution. Neutralization occurs when each H30 ion combines with an OH ion to form two molecules of H2O. Chemists found the reaction of any strong base with any strong aci d always produced 56 kJ/mol (A/y = —56 kJ/mol), which was consistent with Arrhenius hypothesis describing neutralization. 18.4 Strong acids and bases dissociate completely into ions when dissolved... 

Arrhenius in 1887 had suggested that many properties of electrolytes could be explained by a dissociation hypothesis The neutral molecules AB of the electrolyte dissociate to form ions A and B , and this dissociation is governed by an equilibrium... 

Subsequent research has entirely confirmed the theory of Arrhenius. The chemical and electrochemical behaviour of solutions is closely connected with their ionic dissociation, and would be quite inexplicable without this theory. Rarely in the history of science has an idea proved so fruitful and suggestive, and led to the discovery of so many hitherto unsuspected relationships as this hypothesis of Arrhenius. 

On the whole hypothesis (1) appears to be the correct one 1 It will be observed that in the treatment here followed we are not considering the more recent investigations of Ghosh, Bjerrum and others who have come to the conclusion that in solutions of strong electrolyte dissociation is complete and therefore the Arrhenius expression is incorrect... 

The dissolution of a salt in water was described by Arrhenius as a dissociation of the salt in positive and negative ions of free mobility. This was originally a difficult suggestion to accept because salts were very stable substances. Therefore, for a long time the theory was called Arrhenius dissociation hypothesis. Later it became clear that the process was a reaction of the solvent water with the ions and that the ion-dipole interaction provided the necessary energy for the compensation of the strong lattice energies. For example, the process can be formulated for sodium chloride by the equation... 

The first hypothesis on the conductibility of ions in electrolytic solutions and on the electrolyte dissociation of acid and basis of the young Swedish chemist Svante August Arrhenius (1859-1927) was not well accepted in his own country. He searched abroad a support for his studies and obtained it from Ostwald and Van t Hoff. He worked with them for six years between 1885 and 1891 and wrote an important paper in 1887 (Arrhenius, 1887). From thereafter his theories on ionic mobility received attention and acceptance and he won the Nobel Prize for chemistry in 1903. After the german period he returned to Sweden and studied the application of Physical chemistry to biology processes giving the basis for Biochemistry (Arrhenius, 1915). 

His three early Leipzig papers (5-7) represent a synthesis of concepts that he was well qualified to make. Working in Ostwald s laboratory, he must have absorbed some of the mass of electrochemical information which appeared a few years later in Ostwald s two-volume work on the history and theory of electrochemistry (H). He was thoroughly familiar with the second-law thermodynamics of Thomson and Clausius, and with the more recent pronouncements of van t Hoff and Helmholtz. Nernst was also imbued with the atomism of Dalton and Boltzmann, in v hich respect he differed from Ostwald and Helmholtz, and he had accepted Arrhenius s recently published (12,13) hypothesis of the complete dissociation of strong electrolyses in solution. However, his conductance work in Kohlrausch s laboratory had given him a lively appreciation of the effects of incomplete ionization of weak electrolytes. 

We see that the hypothesis that electrolytes dissociate into ions, put forward by Arrhenius almost a hundred years ago, can account for the deviations from the ideal behavior of extremely dilute solutions. 

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