The Empirical Laws of Acid-Base Catalysis

The Empirical Laws of Acid-Base Catalysis 1. Salt Effects 

The subject of salt effects in one which arises in all reaction-kinetic problems involving electrolytes and has no special relevance to acid-base catalysis. However, much of the early work on salt effects was in fact carried out with catalyzed reactions, and a neglect of these effects is still the commonest cause of misinterpretation of data on acid-base catalysis, so that a brief account will be given here. It is convenient to include under the heading of salt effects the various ways in which the assumptions of the classical theory have been modified by modern views on electrolytic solutions. Since the catalyst itself is commonly ionic, the same problems often arise even when no other electrolyte has been added to the system. 

It is not strictly true to say that the velocity of a reaction catalyzed by a strong acid or a strong base is universally or exactly proportional to the catalyst concentration. In the first place, this statement ignores the primary salt effect (see below), though deviations attributable to this cause are unlikely to exceed a few per cent in 0.1 N solution. In the second place it is once more becoming fashionable to describe such salts 

1 N acetic acid 0.075 N acetic acid 0.05 N acetic acid 0.025 N acetic acid 

This principle of maintaining a constant ionic strength is of great value in simplifying the comparison of kinetic data and should be followed whenever possible. 

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