ABSTRACT
If a source of H+ or -OH is present other than the water itself, that is the ions are present at a concentration greater than 10-7 M, then the solution is acidic. Conversely, if the concentration of H+ is less than 10-7 M (hence [-OH ] is greater than 10-7 M) the solution is referred to as alkaline or basic. There is, however, a more convenient way of expressing the acidity or basicity (alkalinity) of a solution and that is by using the pH scale. The pH of a solution is simply the logarithm (to the base 10) of the reciprocal of the hydrogen ion activity, which under conditions of dilute solutions may be approximated to the concentration, as follows;
pH = -log [H+]
Therefore,
Of course, as both K a and K
also be applied to these terms. Thus;
pK a + pK
The pH scale is thus a convenient system for specifying the acidity of a solution in terms of small, and for the most part, positive numbers, over the range 0 to 14, in general.
