iii Here, it is illustrated for the value r = 1 and ∆pK c a = 2.527, more or less corresponding to trivalent species -Rilbe found ∆pK c a = 2.58 for trivalent species, which is rather close . Obviously, these two situations are different and it is no more surprising to find different values of ∆pK c a than it was when comparing mixtures of two monovalent acids with divalent species in section 3.2.1.