General View of M-L Systems

Let us illustrate the significance of a Kj = 7 by calculating the fraction complexed in 0.1 M potassium sulfate solution. From equation (2-4) of Chapter 2, we get / = 0.3, which leads to /2 = 0.25 from the Davies equation or chart. We assume that the other two / factors cancel. We have 

12% of the K and 24% of the SOI originally added are in associated form. This significantly affects the solubility of CaS04 in the case studied in Chapter 10. 

for example, may be in OH , RCOO , ROH, etc. The order is only roughly constant. The acid ions are arranged into three groups hard, borderline, and soft as ordered in Table 8-2. 

In Table 8-2, we can see that the hard acids form more stable, higher K, complexes with hard bases and similarly for the soft acids with soft bases. The trends across the table are reversed roughly as we move from top to bottom. Examples are hard-hard, AIF (log Ki 6.2) soft-soft, HgCN (log Ki 18) hard-soft, HgF (log Ki 1.6). Often, but not in all cases, hard-soft and soft-hard combinations are weaker interactions. 

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