Page:Text-book of Electrochemistry.djvu/180

 dissociation of salts with the dilution has been suggested by van't HoflF {11), namely —

whilst Ostwald's formula can be expressed in the form —

Cj denotes the concentration of each ion (it is the same for both) expressed in gram-ions per litre, and C^ is the concentration of the undissociated part of the electrolyte expressed in gram-molecules per litre.

Others, among them Storch (^^), have expressed the dilution law in the form- *

and have experimentally determined the value of the exponent n, which has been found to vary for electrolytes of diflFerent strengths, but in general is not very different from the value 1*5 contained in van't HoflTs form.

A possible explanation of this peculiar deviation from the law of mass action is that the addition of the ions of a strong electrolyte considerably increases the dissociating power of the water. If this be correct, the dissociation constant of the dissolved substance should be an increasing function of the quantity of salt ions dissolved in the water. This action of the ions recalls the much weaker and opposite eflfect of some non-electrolytes (see p. 150). The assumption is supported by some experiments in which the dissociation equilibrium of weak acids was determined in presence of salts (JiS), These experiments show that the dissociation constants of the weak acids increase in the same way with increasing salt concentration as do the constants for the salts ; there is, however, a quantitative difiference, and in the case of the salts their own ions form the active material. Whatever be the explanation, it may be regarded as certain

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