EQUILIBRIA OF THE H-MOO42--CH3PO32- SYSTEM IN AQUEOUS 1.0 M NA(CL) MEDIUM()

The equilibria pH(+) + qMoO(4)(2-) + rCH(3)PO(3)(2-) reversible arrow (H+)(p)(MoO42-)(q)(CH3PO32-)(r) have been investigated at 25.0 degrees C in 1.000 M Na(el) by the combined emf-NMR method. Quantitative anal ysis of the emf and P-31 NMR data confirmed the existence of the follo wing ternary species, denoted by (p, q, I) according to the general eq uilibria above: (10, 5, 2), (11, 5, 2), (11, 7, 1), (12, 7, 1), and (1 2, 6, 1). Least-squares calculation gave log beta(10, 5, 2) = 69.51 +/ - 0.01, log beta(11, 5, 2) = 71.07 +/- 0.08, log beta(11, 7, 1) = 72.6 9 +/- 0.04, log beta(12,) (7,) (1) = 76.23 +/- 0.05, and log beta(12), (6,) (1) = 70.31 +/- 0.05. The formation constants of the (p, 5, 2) s pecies of the current system and the molybdoselenite system correlate with the pK(a) of the heteroatom source. (C) 1998 Elsevier Science Ltd . All rights reserved.