Sodium Fluoride Ion-Pairs in Seawater.

摘要

Laboratory investigations were conducted on the formation of NaF ion-pairs at the ionic strength of seawater using specific ion electrodes. Sodium and fluoride ion electrodes produced results which are consistent with the ion-pairing model for these ionic interactions. The stoichiometric association constant for NaF, K*(NaF) was determined at 15, 25, and 35 C. It was assumed that K*(NaF) was a function of temperature, pressure, and ionic strength but not of solution composition. The value of K*(NaF) at 25 C and I = 0.7 m is 0.045 + or - 0.006. K*(NaF) increased with decreasing temperature. This result was used to recompute values of K(MgF) and K(CaF) accounting for the presence of NaF ion-paris. The value for K*(NaF) indicates that 1.1 % of the fluoride in seawater is ion-paired with sodium at 25 C and 35% salinity. This fraction increases to approximately 2% at the lower temperatures found in the deep ocean. The percentage of free fluoride in natural seawater was measured at 15, 25, and 35 C to verify the specification calculated from equilibrium constants. (Author)