Principal species

FIGURE 27 2 The titration curve of glycine At pH values less than pKs H3NCH2CO2H is the major species present At pH values between pKs and pK z the principal species is the zwitter... 

Acid Deposition. Acid deposition, the deposition of acids from the atmosphere to the surface of the earth, can be dry or wet. Dry deposition involves acid gases or their precursors or acid particles coming in contact with the earth s surface and thence being retained. The principal species associated with dry acid deposition are S02(g), acid sulfate particles, ie, H2SO4 and NH HSO, and HN02(g). Measurements of dry deposition are quite sparse, however, and usually only speciated as total and total NO3. In general, dry acid deposition is estimated to be a small fraction of the total... 

Soil Nutrient. Molybdenum has been widely used to increase crop productivity in many soils woddwide (see Fertilizers). It is the heaviest element needed for plant productivity and stimulates both nitrogen fixation and nitrate reduction (51,52). The effects are particularly significant in leguminous crops, where symbiotic bacteria responsible for nitrogen fixation provide the principal nitrogen input to the plant. Molybdenum deficiency is usually more prominent in acidic soils, where Mo(VI) is less soluble and more easily reduced to insoluble, and hence unavailable, forms. Above pH 7, the soluble anionic, and hence available, molybdate ion is the principal species. 

The hydrolysis equilibria for H2Cr04 given in Table 3 are only valid in HNO or HCIO solutions. Other acids yield complexes such as those shown for chloride and bisulfate ions. The exact composition of chromate(VI) anion(s) present in aqueous solution is a function of both pH and hexavalent chromium concentration (68). However, at pH values above 8, virtually all the Cr(VI) is present as the CrO anion. When the pH is between 2 and 6, an equilibrium mixture of HCrO and Ci2 is present when the pH is below 1, the principal species is H2Cr04 (68,69). At very high Cr(VI) concentrations... 

Nitrogen forms numerous oxoacids, though several are unstable in the free state and are known only in aqueous solution or as their salts. The principal species are summarized in Table 11.12 of these by far the most stable is nitric acid and this compound, together with... 

In aqueous solution increase in pH results in progressive deprotonation, dehydration and dimerization, the principal species being [(HOhlOj]. [(HOblO,]", [(HOlsIO l -,... 

Quinoxalin-2-one is a very weak base (pK — 1.37) and so the different orientation of substitution in acetic and sulfuric acids may mean that in acetic acid the principal species undergoing nitration is the neutral molecule, and in sulfuric acid, the mono-cation. Treatment of quinoxaline-2,3-dione, or its iViV -dimethyl derivative in sulfuric acid, with 1 equivalent of potassium nitrate, results in nitration at position 6 with 2 equivalents of potassium nitrate, 6,7-dinitro compounds are formed. When quinoxaline is boiled with aqueous nitric acid, 6-... 

L he principal species Cr. ia which the oil bas actually been distilled and examined are the [o]lowing —... 

At this intermediate pH, the zwitterion is the principal species present. Its concentration is much higher than that of either cation or anion. 

Relative concentrntions of different glycine species as a function of pH. Between about pH 3 and 9, the zwitterion is the principal species it has its maximum concentration at pH 6. the isoelectric point Below pH 2. the cation dominates above pH 10. the anion is the principal species. 

Aspartic acid acts as a triprotic acid with successive dissociation constants of 8.0 x 10-3, 1.4 X 10-4, and 1.5 X 10-10. Depending upon pH, aspartic acid can exist in four different forms in water solution. Draw these forms and calculate the pH range over which each form is the principal species. 

We have also carried out preliminary experiments in which we have detected the laser desorption of ethylene, cyanogen, methanol, and benzene from the Pt(s)[7(111) x (100)] surface. These spectra are shown in Figure 9. In the experiments involving ethylene, cyanogen, and methanol only neutral species are desorbed. In the case of benzene we observe the molecular parent ion in the absence of the electron beam. We believe that this is due to resonance multiphoton ionization of the benzene by the laser after desorption (resonance multiphoton ionization of benzene is very efficient with 249 nm radiation). These spectra are in marked contrast to the results of SIMS experiments which produce a wide variety of complex metal-adsorbate cluster ions. In the case of ethylene, our experiments were performed at 140 K, and under these conditions ethylene is known to be a molecular x-bonded species on the surface. In SIMS under these conditions the predominant species is CH (15)t but in the laser desorption FTMS experiments neutral ethylene is the principal species detected at low laser power. 

Figure 3.4 Microspeciation of cetirizine, a three-pi molecule [142], The numeric quantities refer to micro-pKa values. The asterisks denote the principal species at various pH states. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]... 

The CL enhancement of the lucigenin reaction with catecholamines in the presence of HTAH micelles was used for determination of dopamine, norepinephrine, and epinephrine [42], However, the presence of an anionic surfactant, SDS, inhibits the CL of the system. The aforementioned CL enhancement in the presence of HTAH can be explained in the following way the deprotonated forms of the catecholamines are expected to be the principal species present in aqueous alkaline solution due to the dissociation of the catechol hydroxyl groups, and to react with lucigenin to produce CL. The anionic form of the catecholamines and the hydroxide ion interact electrostatically with and bond to the cationic micelle, to which the lucigenin also bonds. Therefore, the effective concentration of the... 

Investigations of the equilibria obtaining in solution have provided information concerning the stoichiometry and stability of the species formed when the beryllium ion is hydrolyzed. Although the identification of the minor species can never be regarded as definitive, there is little doubt that the principal species are Be2(OH)3+ and Be3(OH)3+ in acid solutions and Be(OH)3 and Be(OH)r in strongly basic solutions. Further support for these conclusions is provided by some crystal structures. The structure of [Be3(0H)3(H20)6]... 

Determine the nature of the principal species in both solutions. KHC03 would ionize to produce K+ and HC03. HBr would ionize to produce H+ and Br. ... 

The release of radioactive iodines from BWR circuits, first into the steam phase and then into the turbine hall, has also been considered thermodynamically (75). A re-analysis of some experimental data of Styrikovich et al (97), suggested that iodates were not, as had been tentatively proposed, likely to be present. Styrikovich s prediction of HIO as a principal species under BWR conditions was confirmed, but it was concluded that his experiments had not measured its steam/water partition coefficient. In view of the meagre experimental evidence, however, more work on this system is desirable. 

The principal species of clay minerals. Source-. After Stumm, W. S. and J. J. Morgan (1981). Aquatic Chemistry, John Wiley Sons, Inc., p. 442 and Grim, R. E. (1968). Clay Mineralogy, 2nd ed., McGraw-Hill Publishing Company, p. 159. 

Compared with Rh systems, where the two principal species are well resolved, it can be seen that as well as more Ir species the bands also overlap, making quantification more difficult. Qualitatively some conclusions can be drawn from the spectra. Forster identified for example that in the presence of I", a potent catalyst poison, much of the Ir could still be present as [IrMe(CO)2l3] . Similarly, as [H2O] is increased the carbonylation rate falls. This is consistent with increased [T] since equilibrium [HI] increases with [H2O] as described above, inhibiting the migratory insertion reaction of [IrMe(CO)2l3] . 

QUIN IN.—Quinta or quina.—This important substance, which was discovered by Pelletier in 1820, is found naturally in the bark of several species of cinchona, which inhabit the Eastern slopes of the Cordillera in Bolivia, Peru, and New Granada. Three principal species ofbark occur in commerce—the yellow, true, or Calisaya bark, obtained from cinchona cordi-folia the red, yielded by c. ohlongifolia and tire pale, from c. condamima. It is found, also, though in smaller quantities, In a variety of barks, which are nearly all obtained from trees of the same family, the distinctive characteristics of which are but imperfectly known. 

An example of when you need to know principal species is when you design a chromatographic or electrophoretic separation. You would use different strategies for separating cations, anions, and neutral compounds. 

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