| Summary: | A study has been carried out on the sodium,calcium and cobalt tripolyphosphate systems. The sodium/tripolyphosphate system has been examined, using prototype sodium electrodes and evidence presented for the form- ation of the complex Na2P3O10 3- as well as for NaP3O10 4- and 3- NaHP3O10 3- . The stability constants for each of these complexes has been obtained, the values for the logarithm of the constants being 0.72, 1.48 and 0. 8 respectively, at I = 0.15. Values for NaP3O10 4- and Na2P3O10 3- were also obtained at I = 0.04 and extrapolation values at I = 0. 0 determined. Ion exchange techniques have been applied to the caloium/ tripolyphosphate solutions resuiting in the following values for the logarithm of the stability constants of the complexes CaP3O10 3- and CaHP3O10 2- , 6.25 and 4.31 at I = 0.15. Other results obtained for CaP3O10 3- at different ionic strengths enabled a value for the stability constant at I = 0.0 to be found. It was also found possible to correct for the sodium complexing taking place. In the studies of the cobalt/tripolyphosphate solutions, ion exchange, potentiometric and spectrophotometric methods were employed. The data obtained has been interpreted as showing the occurrence of the following complexes, CoP3O10 3- , CoHP3O10 2- , Co(P3O10)2 8-, CoH(P3O10)2 7-, Co(PH3O10)2 6-, Co(OH)P3O10 4- and Co(OH)2P3O10 5-. The values obtained for the logarithm of the stability constants of the first five complexes at I = 0.5 are 6.5, 5.0, 12.6, 10.6 and 9.4 and for the last two complexes at I=1 ,0, 11.5 and 15.2. Values were alos obtained for the com- plexes CoP[3]O10[3-], CoHP[3]O[10][2-] and Co(OH)P[3]O[10][4-] at different ionic strengths. Evidence is presented which shows that the cobalt complexes studied change from an octahedral to a tetrahedral arrangement of ligands on increasing the pH above 10.
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