Barium stability constant

There is an appreciable difference between the stability constants of the CDTA complexes of barium (log K = 7.99) and calcium (log K = 12.50), with the result that calcium may be titrated with CDTA in the presence of barium the stability constants of the EDTA complexes of these two metals are too close together to permit independent titration of calcium in the present of barium. 

Even though the stability constants for calcium, barium and strontium cations in nitrobenzene are much higher than that for lithium cation, the translocation of lithium ion from water to nitrobenzene is shifted by about 300 mV negatively when it is used as a base electrolyte, i.e., when [Li+(w)]>>[X(n)] and it coincides with the transfer of alkaline earth metal cation. From a comparison of the standard electrical potential difference and from the calculated half-wave potentials using the stability constant for several cations we have chosen magnesium chloride as a base electrolyte for the aqueous phase. To minimize the base electrolytes current in DPSV we have decreased their concentrations. In the case of magnesium chloride it was 2.5 mM solution in water and 5 mM solution of TBATPB in nitrobenzene. The concentration of the ionophore was 1 mM. 

A more highly charged cation should polarize the oxygen atoms more readily, making the electron pairs more available for coordinate bonding. Potassium and barium cations are approximately the same size, and yet the barium complex of 18-crown-6 has a stability constant greater than that for the potassium complex. 

Faucherre (1954) studied the hydrolysis reactions of aluminium(III) in barium nitrate media. They proposed stability constants for both Al2(OH)2 and AlOH at 20°C at two different medium concentrations. The constants proposed in the study appear to be relatively consistent with those obtained in other media for both species. The stability constants obtained by the study are noted by the present review but are not retained. 

In contrast to the ionic complexes of sodium, potassium, calcium, magnesium, barium, and cadmium, the ease with which transition metal complexes are formed (high constant of complex formation) can partly be attributed to the suitably sized atomic radii of the corresponding metals. Incorporated into the space provided by the comparatively rigid phthalocyanine ring, these metals fit best. An unfavorable volume ratio between the space within the phthalocyanine ring and the inserted metal, as is the case with the manganese complex, results in a low complex stability. 

To gain an insight into the sulfide stabilization, examine the solubility product constants for the sulfides and phosphates of hazardous metals listed in Table 16.4. In this table, except for barium sulfide, other sulfides as well as phosphates have very high pK p, indicating that their aqueous solubility is almost negligible. In particular, the pA sp of HgS and Ag2S is very high, and these two sulfides are insoluble in water. Therefore, when a waste stream contains one of these two, sulfide pretreatment followed by phosphate ceramic formation is an ideal way to treat the waste stream. 

Lead magnesium niobate, Pb(Mg 3Nb2/3)03, is a ferroelectric relaxor material which is paraelectric at room temperature. The perovskite phase is typically modifield with addition of lead titanate or barium titanate, which raises the Curie temperature to near room temperature. Very high dielectric constants can be achieved, >20,000, but at the expense of temperature stability. 

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