Neutralization Potential

Equation 2.94 can be used to calculate alkalinity by considering the following  

Note that Equation 2.95 does not include the H2C03 component, which is part of CT (Eq. 2.84). 

A more appropriate way of expressing alkalinity and/or acidity of acid waters emanating from natural environments is by defining the term commonly known as neutralization potential (NP)  

If the solution to Equation 2.96 gives a negative number, this value is considered to be acidity. However, if the solution gives a positive number, this value is considered to be alkalinity. 

Alkalinity of effluents in natural systems is often controlled by carbonate minerals. The most common carbonate mineral in the environment is limestone (CaC03). The factors that affect CaC03 solubility are pH and pC02. The equations that one needs to consider in estimating solubility and alkalinity are 

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In Fig. 2 are depicted anion and neutral potential curves that are qualitatively illustrative of (lb,4d) the X II NH case mentioned earlier. In this anion, the HOMO is a non-bonding 2pn orbital localized almost entirely on the N atom. As such, its LCAO-MO coefficients are not strongly affected by motion of the N-H bond (because it is a non-bonding orbital). Moreover, the anion and neutral surfaces have nearly identical Re and a>e values, and similar De values, as a result of which these two sur ces are nearly parallel to one... 

In Fig. 4 are shown anion and neutral potential curves, as functions of the twist angle of the H2C-C bond in a typical enolate anion (2,4e) such as... 

By introducing the simplest semi-classical approximation to the propagators, in which the nuclear motion kinetic energy is assumed to commute with the anion and neutral potential energy functions and with the non BO coupling operators, one obtains... 

After publication of the ion-storage-ring data, new recombination mechanisms were proposed1 that do not require crossings between ionic and neutral potential curves. However, no detailed calculations have been made for Hj and it is not yet clear if such mechanisms are capable of explaining the experimental findings. 

Jambor, J.L., Dutrizac, J.E., Groat, L.A., Raudsepp, M. 2002. Static tests of neutralization potentials of silicate and aluminosilicate minerals. Environmental Geology, 43, 1-17. 

Determination of neutralization potential in the prediction of acid rock drainage. Proceedings of the 4th International Conference on Acid Rock Drainage, Vancouver, 2, 449-464. 

In collaboration with Jon Belisle, octanol pKa values were measured for a series of benzoic acids and phenols. A coupled electrode calibrated in aqueous buffers was used. The haIf-neutralization potential was measured since the Renderson-Hasselbalch equations would not apply. The titrant was 0.1 sodium hydroxide in isopropanol methanol 4 1. The titrant was only 6% of the total volume at half-neutralization, so the medium was essentially octanol-like. The results are listed in Table I and some benzoic acid values are plotted in Figure 6. 

Figure 6, HaIf-neutralization potentials of benzoic acids in water-saturated octanol vs their corresponding aqueous pKa values.

The lowering of the resonance energy due to a deeper ion-neutral potential in comparison with neutral neutral potential of the vdW molecule... 

When the 0.5 moles of Fe2+ liberated in (5) are oxidized to form Fej J, a further 0.5 moles of protons are consumed (according to reaction (3)). The ultimate hydrolysis of this Fe3+ to form solid Fe(OH)3 (according to reaction (4)) will yield 1.5 moles of H+. Thus the overall proton balance, J](H1), can be summarized as (H+) = -2 - 0.5 + 1.5 = - 1. Hence, for every mole of stoichiometric ankerite dissolved, there is a net consumption of one mole of proton acidity. Given that most ankerites contain rather less Fe2+ than Mg2+ (Smythe Dunham 1947), in the majority of cases, the net consumption of protons will be greater than one. Thus, in contrast to the case of siderite, ankerite does possess net neutralization potential for acidic waters. 

The influence of substituents in mono- and disubstituted 2,3-dimethyl-quinoxalines and their conjugate acids on the UV and NMR spectra have been correlated with a,196 while stretching frequencies of the carbonyl group of 6-substituted quinazolinediones and their half-neutralization potentials have been related to ctp.197... 

Andronati and co-workers reported a detailed study of the A-basicity of compounds 203 (X = H, Me R1 = H R2 = H, Br, Cl, Me) which contain amide, imine, and amine nitrogens in one molecule. The basicities, obtained from the half-neutralization potentials in potentiometric titrations, showed 203 to be monoacidic bases the basicity varied predictably with substitution and fell between the stronger quinoxaline-2-ones and the weaker l,4-benzodiazepine-2-ones. Ultraviolet spectroscopic studies demonstrated that the amino, not the imino, nitrogen was N-protonated (83CHE337). 

Fig. 6.6. Relationship between pKb(water) of N-bases and half - neutralization potential El/2 for potentiometric base titration in glacial acetic acid. 1) 4-aminopyridine (4.83), 2) morpholine (5.30), 3) 2,4,6-trimethylpyridine (6.68), 4) pyridine (8.85), 5) p-toluidine (8.88), 6) o-toluidine (9.61), 7) 3-acetylpyridine (10.82), 8) chloroaniline (11.36), 9) pyrazole (11.47), 10) diphenylamine (13.10) (Pawlak et al., 1985)...

Ec, at which the uncertainly in R, AR, is comparable to the separation of the ionic and neutral potential. The uncertainty of R can be regarded to be analogous to the range parameter, L, of the Demkov-Komarov model that defines the width of the crossing region. In the work of Aberle and coworkers on rare gas + H collision systems, a range parameter, L, of <0.1 A is determined. 

Numerous types of static tests have been developed, and some of the laboratory procedures and the variety of tests or their individual developments have been described in various publications, such as those by MEND (1991), Lawrence and Wang (1997), Morin and Hutt (1997), White et al. (1999), and Jambor (2003). By far the most widely adopted static test, both for metalliferous and coal deposits, is the acid-base account (ABA) of Sobek et al. (1978). As is implied by its name, ABA involves a determination of the acid-producing potential (AP) of a sample, and a determination of the base that is potentially releasable the latter is generally referred to as the neutralization potential (NP). The two chemically determined values therefore provide a net accounting of the expected behavior during weathering. A common form of expressing the result is to obtain the net NP (NNP) by simple subtraction of the two chemically determined values ... 

Finally, we have considered the half-neutralization potentials (HNP) of 4-substituted N,iV-dimethylanilines in 2 1 chloroform-acetic acid . The best regression equation is ... 

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