NaCl-PbCl

This section is based upon the papers of Johnson and Pytkowicz (7j and of Sipos et al. (8). The concepts used are the formation of coulombic ion-pairs between the major ions of seawater (NaCio, NaHC03°, NaC03", NaS04, and similar pairs for Ca2+ and Mg2+) and the formation of true complexes such as PbCl+, PbCl2°. CdCl+, PbOH+, PbC03o, etc. The coexistence of these two types of entities implies competition, e.g., for Cl ions, one has NaCl° and PbCl+, and yields trace metal speciation quite different from those obtained in the absence of ion pairs. In Table IV are shown the fractions of the major ions which are free and ion-paired. 

Characterization of the complexing reaction was then conducted in the presence of 0.83 m sodium chloride in the aqueous phase over a temperature range 15°-60°C. In addition, removal of Hs PbCl as a function of the re-agent-to-organic lead ratio Cr/Cl in the presence of 5 wt % NaCl was examined at 30° C using in turn three other dithiocarbamate reagents besides that of sodium diethyl dithiocarbamate. 

If one prepares a solution of 1 mol L-1 NaCl, it is not clear whether there will be 1 mol L 1 Na+ or 1 mol L 1 Cl-, because the two ions may react with each other or with other chemical species in solution to form additional solution species with different valencies. For example, assuming that the NaCl solution contains also lead (Pb2+), Pb2+ and Cl- would react with each other to form the dissolved chemical species PbCl+, PbCl2, and so on. Chemists distinguish the two situations (free vs. paired solution species) by referring to the total dissolved concentration of an element as formality (F), and to the concentration of certain known dissolved chemical species (e.g., Na+ and Pb2+) as molarity (M) (Table 1.9). Field practitioners of environmental chemistry almost always refer to concentrations of elements because it is total dissolved concen-... 

Base AlCl, 72-15 KCl 64-75 NaCl AmCl 54-4 50-98 ZnOlj 57 56 FeCl, 51-35 CoCI, PbCl, SnCl, 56-5 72-69 64-94 ... 

The striking effect of the alkali metal cation on the physical properties of mixed melts of this sort is shown particularly well in a comparison of the PbCla-KCl and PbCl-s-NaCl systems. As described by Bloom (1959), the latter shows a simple phase eutectic, only slight deviations in the equivalent conductivity and activation energy (negative and positive, respectively), linear molar volumes, and PbCh and NaCl activities which deviate little from ideality. The surface tensions of the PbCh-MCl systems regularly change from a linear relationship with LiCl to an even deeper minimum than illustrated in Fig. 3 (c) for CsCl. 

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