Ionic identity

It is easy to distinguish Ba + ions from Na+ for several reasons. Firstly, their atomic scattering factors are quite different, 54 e for Ba2+ vs 10 e for Na+. Secondly, their ionic radii are quite different, Ba2+ = 1.34 X and Na = 0.97 X (5). Also, the approach distances between these ions and zeolite oxide ions in dehydrated Na 2 A (16) and hydrated Bag-A are known (see Table III). Finally, the requirement that 12 cationic charges be placed per unit cell does not allow the major positions to refine to acceptable occupancies with an alternative assignment of ionic identities. 

The study described here demonstrates that ESCA provides information regarding the chemical nature of the surface of an unperturbed sample which would be difficult to acquire by other methods. A major weakness of ESCA, the necessity of exposing the sample to vacuum, together with its attendant problem of sample volatilization, can also be one of its strengths. The volatility of some nitrogenous species in atmospheric aerosol particles can be used to provide strong evidence for chemical identity of ionic compounds (e.g., ammonium nitrate) rather than simply ionic identities as provided by wet chemical methods. This volatility is accelerated by x-ray irradiation, so that similar results could be achieved only by extended vacuum exposure alone if another analytical technique were used. Also, with ESCA, volatile losses can be conveniently monitored since the sample remains in the spectrometer throughout the process. 

As noted in Section 3.2.1, multiplier gain can depend not merely on ionic mass for a fixed ion energybut also on ionic identity correction factors as large as 1.8 have been reported for this effect. Except in the case of pulse counting, such correction factors must be measured and applied and it is often not clear in the literature if this has been done. It must be stated. It would be useful, too, if the quantitative values for the correction factors were reported. Ryan and Futrell report, for example, an uncorrected rate constant of 0.96 x 10 cm molecule" sec" for the reaction CH4" (CH4,CH3)CHj , a value which was raised to 1.70 x 10" cm molecule sec" when the measured multiplier correction was applied. The currently accepted value for this rate constant is 1.2 x 10 cm molecule sec". Was the correction factor in error for that particular experiment or did the method yield an anomalously high rate constant Values in the literature for these correction factors would help to answer such questions.f... 

Catalysis in a single fluid phase (liquid, gas or supercritical fluid) is called homogeneous catalysis because the phase in which it occurs is relatively unifonn or homogeneous. The catalyst may be molecular or ionic. Catalysis at an interface (usually a solid surface) is called heterogeneous catalysis, an implication of this tenn is that more than one phase is present in the reactor, and the reactants are usually concentrated in a fluid phase in contact with the catalyst, e.g., a gas in contact with a solid. Most catalysts used in the largest teclmological processes are solids. The tenn catalytic site (or active site) describes the groups on the surface to which reactants bond for catalysis to occur the identities of the catalytic sites are often unknown because most solid surfaces are nonunifonn in stmcture and composition and difficult to characterize well, and the active sites often constitute a small minority of the surface sites. 

Note that the unit for ionic strength is molarity, but that the molar ionic strength need not match the molar concentration of the electrolyte. For a 1 1 electrolyte, such as NaCl, ionic strength and molar concentration are identical. The ionic strength of a 2 1 electrolyte, such as Na2S04, is three times larger than the electrolyte s molar concentration. 

Several features of equation 6.50 deserve mention. First, as the ionic strength approaches zero, the activity coefficient approaches a value of one. Thus, in a solution where the ionic strength is zero, an ion s activity and concentration are identical. We can take advantage of this fact to determine a reaction s thermodynamic equilibrium constant. The equilibrium constant based on concentrations is measured for several increasingly smaller ionic strengths and the results extrapolated... 

Ionic polymerizations are almost exclusively solution processes. To produce monodisperse polymers or block copolymers, they must be mn batchwise, so that all chains grow for the same length of time under identical conditions. 

Commercial grades of socbum aluminate contain both waters of hycbation and excess socbum hycboxide. In solution, a high pH retards the reversion of socbum aluminate to insoluble aluminum hycboxide. The chemical identity of the soluble species in socbum aluminate solutions has been the focus of much work (1). Solutions of sodium aluminate appear to be totaby ionic. The aluminate ion is monovalent and the predominant species present is deterrnined by the Na20 concentration. The tetrahydroxyaluminate ion [14485-39-3], Al(OH) 4, exists in lower concentrations of caustic dehydration of Al(OH) 4, to the aluminate ion [20653-98-9], A10 2) is postulated at concentrations of Na20 above 25%. The formation of polymeric aluminate ions similar to the positively charged polymeric ions formed by hydrolysis of aluminum at low pH does not seem to occur. Al(OH) 4 has been identified as the predominant ion in dilute aluminate solutions (2). 

Most ingredients in a detergent formulation contribute to the ionic strength of the wash solution. The effect of ionic strength on protease performance depends on pH and enzyme identity. The pH wash solutions also affects protease performance (Pig. 8). 

The diffraction mechanisms in XPD and AED are virtually identical this section will focus on only one of these techniques, with the understanding that any conclusions drawn apply equally to both methods, except where stated otherwise. XPD will be the technique discussed, given some of the advantages it has over AED, such as reduced sample degradation for ionic and organic materials, quantification of chemical states and, for conditions usually encountered at synchrotron radiation facilities, its dependence on the polarization of the X rays. For more details on the excitation process the reader is urged to review the relevant articles in the Encyclopedia and appropriate references in Fadley. ... 

The dissociation constants are thermodynamic constants, independent of ionic strength. Equation (8-33), which was derived from (8-30), is, therefore, identical in its form, and its salt effect, with Eq. (8-31). Therefore, salt effects cannot be used to distinguish between Eqs. (8-30) and (8-31). Another way to express this is that if kinetically equivalent forms can be written, it is not possible to determine, on the... 

The effect of the lanthanide contraction on the metal and ionic radii of hafnium has already been mentioned. That these radii are virtually identical for zirconium and hafnium has the result that the ratio of their densities, like that of their atomic weights, is very close to Zr Hf = 1 2.0. Indeed, the densities, the transition temperatures and the neutron-absorbing abilities are the only common properties of these two elements which differ... 

The viscosities of non-haloaluminate ionic liquids are also affected by the identity of the organic cation. For ionic liquids with the same anion, the trend is that larger allcyl substituents on the imidazolium cation give rise to more viscous fluids. For instance, the non-haloaluminate ionic liquids composed of substituted imidazolium cations and the bis-trifyl imide anion exhibit increasing viscosity from [EMIM], [EEIM], [EMM(5)IM], [BEIM], [BMIM], [PMMIM], to [EMMIM] (Table 3.2-1). Were the size of the cations the sole criteria, the [BEIM] and [BMIM] cations from this series would appear to be transposed and the [EMMIM] would be expected much earlier in the series. Given the limited data set, potential problems with impurities, and experimental differences between laboratories, we are unable to propose an explanation for the observed disparities. 

Comparison of the dimerization of 1-butene with [(H-COD)Ni(hfacac)] in chloroaluminate ionic liquids with the identical reaction in toluene is quite instructive. First of all, the reaction in the ionic liquid solvent is biphasic with no detectable... 

Interestingly, the specific environment of the ionic solvent system appears to activate the chiral Ni-catalyst beyond a simple anion-exchange reaction. This becomes obvious from the fact that even the addition of a 100-fold excess of Fi[(CF3S02)2N] or Na[BF4] in pure, compressed CO2 produced an at best moderate activation of Wilke s complex in comparison to the reaction in ionic liquids with the corresponding counter-ion (e.g., 24.4 % styrene conversion with 100-fold excess of Fi[(CF3S02)2N], in comparison to 69.9 % conversion in [EMIM][(CF3S02)2N] under otherwise identical conditions). 

The effects of increasing the concentration of initiator (i.e., increased conversion, decreased M , and broader PDi) and of reducing the reaction temperature (i.e., decreased conversion, increased M , and narrower PDi) for the polymerizations in ambient-temperature ionic liquids are the same as observed in conventional solvents. May et al. have reported similar results and in addition used NMR to investigate the stereochemistry of the PMMA produced in [BMIM][PFgj. They found that the stereochemistry was almost identical to that for PMMA produced by free radical polymerization in conventional solvents [43]. The homopolymerization and copolymerization of several other monomers were also reported. Similarly to the findings of Noda and Watanabe, the polymer was in many cases not soluble in the ionic liquid and thus phase-separated [43, 44]. 

One of the most important parameters that defines the structure and stability of inorganic crystals is their stoichiometry - the quantitative relationship between the anions and the cations [134]. Oxygen and fluorine ions, O2 and F, have very similar ionic radii of 1.36 and 1.33 A, respectively. The steric similarity enables isomorphic substitution of oxygen and fluorine ions in the anionic sub-lattice as well as the combination of complex fluoride, oxyfluoride and some oxide compounds in the same system. On the other hand, tantalum or niobium, which are the central atoms in the fluoride and oxyfluoride complexes, have identical ionic radii equal to 0.66 A. Several other cations of transition metals are also sterically similar or even identical to tantalum and niobium, which allows for certain isomorphic substitutions in the cation sublattice. 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

Fig. 4.1.17 Graphic illustration of Forster-type resonance energy transfer from aequorin to Aequorea GFP. In the vessel at left, a solution contains the molecules of aequorin and GFP randomly distributed in a low ionic strength buffer. The vessel at right contains a solution identical with the left, except that it contains some particles of DEAE cellulose. In the solution at right, the molecules of aequorin and GFP are coadsorbed on the surface of DEAE particles. Upon an addition of Ca2+, the solution at left emits blue light from aequorin (Xmax 465 nm), and the solution at right emits green light from GFP (Xmax 509 nm).

The bioluminescence spectrum of P. stipticus and the fluorescence and chemiluminescence spectra of PM are shown in Fig. 9.7. The fluorescence emission maximum of PM-2 (525 nm) is very close to the bioluminescence emission maximum (530 nm), but the chemiluminescence emission maximum in the presence of a cationic surfactant CTAB (480 nm) differs significantly. However, upon replacing the CTAB with the zwitter-ionic surfactant SB3-12 (3-dodecyldimethylammonio-propanesulfonate), the chemiluminescence spectrum splits into two peaks, 493 nm and 530 nm, of which the latter peak coincides with the emission maximum of the bioluminescence. When PM-1 is heated at 90°C for 3 hr in water containing 10% methanol, about 50% of PM-1 is converted to a new compound that can be isolated by HPLC the chemiluminescence spectrum of this compound in the presence of SB3-12 (curve 5, Fig. 9.7) is practically identical with the bioluminescence spectrum. 

Accordingly, the ionic conductivity in an electrolyte with negligible electronic conduction (/jon jtolal) may be determined by Ohm s law, provided that unpolarizable electrodes are employed. To overcome this limitation, separate voltage probes in the shape of identical electronic leads connected to the electrolyte at positions separated by a distance L may be employed (four-probe technique [38]). Under these... 

---