From the relations 2.12 and 2.13, the pH value of a buffer will change with its dilution, because of changes in the ionic strength. Table 2.2 shows the magnitude of the effect of diluting an equimolar solution of a HA/A- buffer (total molar concentration stated) with an equal volume of water The quantity △pH½ is defined as the increase in pH of a solution when it is diluted in this way. Dilution of acidic buffers increases the pH; with bases there is a decrease.        
Conversely, the addition of an \'inert\' salt such as NaCl decreases the pH of acidic buffers and increases the pH of basic buffers.         Greater effects are produced when higher ionic charges are involved. For example, for a HA-/A²- buffer (such as KH2PO4, Na2HPO4) dilution with an equal volume of water increases the pH by approximately three times the amount shown in Table 2.2.        

Because of its dependence on the squares of the charges of the ions present, the ionic strength of a buffer can vary over a wide range if di- or higher-valent ions are involved. Thus in the classical Mclivaine phosphate-citrate buffers the ionic strength varies 30-fold between pH 2.2 and pH 8.0. The diffrence in charge of an acid and its conjugate base causes the ionic strength of a buffer to vary with pH unless compensating amounts of a suitable salt are added. Hence, in calculating buffer tables it is necessary to use successive approximations for ionic strengths, activity coefficients and concentrations of the buffer species: computer-based itera-tion is convenient.