CHAPTER XVI 



IONIZATION 



WE have learned in the preceding chapter that acids, bases, 

 and salts in solution exhibit two independent sets of properties, 

 one of which can be referred to the positive) the other to the 

 negative radical. We have seen that the passage of an electric 

 current through such a solution decomposes it, the positive radical 

 of the electrolyte proceeding to the negative electrode, the nega- 

 tive radical to the positive electrode. Finally, we have found that 

 the abnormalities in certain physical properties of these solutions 

 seem to indicate that the radicals actually exist, to a large extent, 

 in an uncombined state in the solution. 



Upon these facts a hypothesis has been based which has proved 

 of considerable assistance in explaining the special properties of 

 conducting solutions. The fundamental idea of this hypothesis, 

 which was first definitely advanced by the Swedish chemist Ar- 

 rhenius in 1887, is now accepted as an established fact. Our 

 knowledge of the field of conducting solutions is still, however, 

 very imperfect, and many important deductions from the hy- 

 pothesis of Arrhenius remain matters of conjecture and dispute. 



The Ionic Hypothesis. In this hypothesis of Arrhenius 

 it is assumed that the molecules of an electrolyte, such as hy- 

 drogen chlqride, are largely broken up in solution into their con- 

 stituent radicals, each radical being electrically charged. These 

 charged radicals have been called ions, and the hypothesis is 

 hence known as the ionic hypothesis. A solution of hydrogen 

 chloride in water is supposed therefore to consist of two parts; 

 (1) an undissociated part, made up of hydrogen chloride molecules 

 HC1; (2) a dissociated or ionized part, made up of equal numbers of 



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