Thus Cu2P2O7(c) is metastable to ,B-Ca2P2O7(c) above pH 2.78 and cannot form. Below this pH, Cu2P2O7(c) can form. Figure 14.4 is drawn to represent the conditions in which more than enough pyrophosphate is present to transform all of the soil-Cu into Cu2P2O7(c). In this case both pyrophosphate minerals would coexist, and Cuz + activity would be governed by Cu2P2O-,(c) through B-Ca2P2O7(c) and soil-Ca. If there were more than enough soil-Cu to dissolve all of the B-Ca2P2O7, the soil-Cu line would continue upward below pH 2.78 and the P2O‘~}` line would be depressed.
Since very few soils are as acid as pH 2.78, the possibility of Cu2P2O7(c) forming in soils is very unlikely.
14.2 HYDRCLYSIS AND SoLUTION COMPLEXES OF Cu(Il)
The hydrolysis reactions of Cuz* are given by Reactions 16 through 20
of Table 14.1 and are plotted in Fig. 14.5. The predominant ion below pH 6.9