Determination of equilibrium constants for a number of metal‐phosphate complexes

Abstract

Laboratory of the Lever's ZepAMaatschappij N.V., Vlaardingen V a n 't Hoff Lzboratory, University of Utreclht Many metal ions form soluble complexes with pyro-and tripolyphosphate. Complex dormation entails a decrease in pH. By measuring the f l and in some cases the concentratism of free metal ions, equilibrium constants for a number of metal-phosphate complexes were determined a t 25" and at 40". Activity corrections were applied. T h e tendency to form complexmes increases in the following order:Cs-K-Na<Li<Ba<Sr<Ca<Mg <Cd -2 n Tripolyphosphate has somewhat stronger complexing properties than pyrophosphate. The influence uf the temperature is in most cases small. Constants obtained are listed in Table V.

Comprehensive Study of the Chelation and Coacervation of Alkaline Earth Metals in the Presence of Sodium Polyphosphate Solution

“…This reaction has been reported for alkaline earth metals that are chelated by tripolyphosphates. 36 The immersion of alkaline phosphate glasses into water instantly leads to a rapid decrease in pH. 20,37 This pH drop is fundamentally similar to the pH decrease that was observed here in polyphosphate solutions.…”

Thermochemistry of the biochemical reaction: { pyrophosphate(aq) + H2O(l) = 2 phosphate(aq)}

“…The results for reactions (24) and (25) given in table 4 can be used to calculate pK values for reactions (15) and (16), respectively. Thus, pK (15) = pK (24) − pK (8) + pK (13) = 4.53.…”

“…The value r H o m = −13.3 kJ · mol −1 was used in performing temperature adjustments to the pK s for reaction (13) reported by Karweik and Huber (30) and Miyajima et al (32) (23) and Sugano et al (29) and will also be used in all subsequent calculations. We judge the electrochemical study of Wolhoff and Overbeek (24) to yield the most reliable pK value for reaction (13). The remaining results are somewhat scattered but the average pK = 7.27 obtained from these other studies is in agreement with the Wolhoff and Overbeek (24) result.…”

“…We judge the electrochemical study of Wolhoff and Overbeek (24) to yield the most reliable pK value for reaction (13). The remaining results are somewhat scattered but the average pK = 7.27 obtained from these other studies is in agreement with the Wolhoff and Overbeek (24) result. For reaction (14) the results of the studies of Lambert and Watters (22) and Irani (25) are in excellent agreement and the average of their pK values has been selected.…”

Influence of Zinc on the Formation of Granules of Calcium Pyrophosphate

“…One explanation for this may lie in the relative stability of the complexes formed by zinc and calcium with pyrophosphate. The binding constants for the metal complex in aqueous solution are 6.8 for calcium and 8.7 for zinc [18]. Thus, in the presence of an excess of pyrophosphate, zinc will effectively compete for pyrophosphate even when present at a concentration 100 fold lower than that of calcium.…”