Consequences of Mass Action Acid-Base Reactions

Consequences of Mass Action Acid-Base Reactions 

The approach used up to now can be applied in the same way for any transformation of substances. In the case of matter dynamics, it does not matter how we imagine the process in question working at the molecular level Whether it is by formation or cleavage of chemical bonds, rearranging crystal lattices, migration of particles, transfer of electrons or whole groups of atoms from one type of particle onto the other, etc. We will concentrate upon one important example here, namely acid-base reactions, in order to demonstrate that the chemical potential is well suited to describing very specialized and differentiated fields. 

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Buffers are capable of absorbing H+ ions (and OH ions) and in this way can resist changes of pH which would otherwise occur with the additions of acids (or bases). This phenomenon can be explained again by the law of mass action. If acid is added to the equilibrium mixture represented by equation (4), the [H+] will rise. But in order to reach equilibrium again, [HA] must also rise the latter can be achieved only by the recombination of H" " and A" to form HA. This reaction consumes nearly all of the added H+ ions, and the consequent change in pH is negligible. All this presupposes, of course, that not too many H+ ions, or not too much acid, have been added. The capacity of the buffer is limited by the nmnber of A ions available to trap H+ ions. 

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