Molar electrical conductivity

The molar electrical conductivity of PBr3 in liquid Br2 is higher than that of PBr3 in Br2-CX4 mixtures (X = C1 or Br).29 The phenomenon has been attributed to a Br" jump mechanism ... 

Chemical transformations of MCMs in aqueous and polar solvents are accompanied by ionization and dissociation. This also can result in the formation of products devoid of the metal. The degree of dissociation depends both on the nature of solvent and the temperature (Fig. 9). This is especially so in the case of transition metal carboxylates, which are strong electrolytes in water. In aqueous or water-oiganic media at pH > 7, salts of unsaturated carboxylic acids are almost completely dissociated (the molar electrical conductivity at infinite dilution, A, , is 146-154cmOhm mol ) hence instead of MCMs, other species such as acrylate and methacrylate ions (specially, metal acrylates and methacrylates) act as monomers. Similarly, in the acrylonitrile-sodium prop-2-enesulfonate system, which undergoes copolymerization in DMSO-H2O mixtures at various pH values (at 45°C with AIBN as the initiator), the relative reactivities of the comonomers change in different media due to the increase in the solvation capacity of water. Actually, copolymerization in these systems involves three types of monomers CH2=CH CH2SO3 Na... 

Aqueous solutions of Cu ", Co " and acrylates are medium-strength electrolytes a plot of the molar electrical conductivity vj. concentration is described satisfactorily by the Kolrausch equation. For 0.05 M aqueous solutions of calcium acrylate (Acr) and methacrylate at 25°C, the specific electrical conductivities, AT, are 5.16 x 10 5 and 2.787 X 10 Ohm mol and the degrees of dissociation, a, are 0.46 and 0.2, respectively. The degrees of dissociation of Zn, Pb, and Ba acrylates (M(Acr)2) in methanol are sufficient for the M(Acr)+ cations that are formed to react with radical initiators (e.g., alkylcobalt chelates with tridentate Schilf bases) to give alkyl free radicals, which induce radical polymeri2ation of MCM even at low temperatures (5-10°C). For other types of MCM ( v-, n-types, see above), metal elimination processes are less typical and in some cases (i.e., chelate type), these processes do not occur at all. 

Miyashita, Nabika, and Suzuki also examined the molar electric conductivity of the reacted compound between the titanocene and MAO [5], The electric conductivity was found as 0.006S cm /mole in toluene, and it was concluded that the active site for polymerization has the structure of a zwitterionic Ti cation center. 

The usual spectroscopic techniques ir, visible/uv and reflectance spectroscopy can be used for characterisation. Measurement of the molar electrical conductivity of solutions and comparing with solutions of simple salts can be used to establish the charges in the ionic components of die complexes. In the case of the chloro-, nitrito and carbonate-complexes, measurements of conductivity and recording of spectra should be done on freshly prepared solutions. KBr discs are preferably used for recording infiared spectra. 

The values of the molar electrical conductivity A of RTlLs result from the direct determination of the specific conductivity k and its multiplication by the molar volume y as yl = kV. On the whole, the specific conductivities of imidazolium RTlLs are larger than those based on pyridinium, pyrrolidinium, and acyclic quaternary ammonium cations, but all are considerably lower than those of concentrated aqueous electrolytes used in batteries, as shown by Galinski et al. [156]. The values of A at 298 K are shown in Table 6.14 as are the parameters and Toa of the VFT expression ... 

The salts had a high electrical conductivity, and it was claimed that the values of the molar conductances at infinite dilution showed the formation of a binary and ternary electrolyte respectively. 

Besides these special physical properties, hydrogen-bonded liquid water also has unique solvent and solution properties. One feature is high proton (H ) mobility due to the ability of individual hydrogen nuclei to jump from one water molecule to the next. Recalling that at temperatures of about 300 K, the molar concentration in pure water of H3O ions is ca. 10 M, the "extra" proton can come from either of two water molecules. This freedom of to transfer from one to an adjacent "parent" molecule allows relatively high electrical conductivity. A proton added at one point in an aqueous solution causes a domino effect, because the initiating proton has only a short distance to travel to cause one to pop out somewhere else. 

The relationship between the diffusional flux, i.e., the molar flow rate per unit area, and concentration gradient was first postulated by Pick [116], based upon analogy to heat conduction Fourier [121] and electrical conduction (Ohm), and later extended using a number of different approaches, including irreversible thermodynamics [92] and kinetic theory [162], Pick s law states that the diffusion flux is proportional to the concentration gradient through... 

Danek and his group have independently proposed a quite similar model, which they call the dissociation modeV - For this model Olteanu and Pavel have presented a versatile numerical method and its computing program. However, they calculated only the electrical conductivity or the molar conductivity of the mixtures, and the deviation of the internal mobilities of the constituting cations from the experimental data is consequently vague. 

When estimating the remaining service life of a polymer material for a particular application, the limiting value should be established of some material property such as tensile strength, elongation at break, electrical conductivity, permeability to low molar mass compounds, the average polymerization degree, etc., at which the polymer does not fail. 

Effective charge and transition-state structure in solution, 27, 1 Effective molarities of intramolecular reactions, 17,183 Electrical conduction in organic solids, 16,159 Electrochemical methods, study of reactive intermediates by, 19, 131 Electrochemical recognition of charged and neutral guest species by redox-active receptor molecules, 31, 1... 

When a solute particle is introduced into a liquid, it interacts with the solvent particles in its environment. The totality of these interactions is called the solvation of the solute in the particular solvent. When the solvent happens to be water, the term used is hydration. The solvation process has certain consequences pertaining to the energy, the volume, the fluidity, the electrical conductivity, and the spectroscopic properties of the solute-solvent system. The apparent molar properties of the solute ascribe to the solute itself the entire change in the properties of the system that occur when 1 mol of solute is added to an infinite amount of solution of specified composition. The solvent is treated in the calculation of the apparent molar quantities of the solute as if it had the properties of the pure solvent, present at its nominal amount in the solution. The magnirndes of quantities, such as the apparent molar volume or heat content, do convey some information on the system. However, it must be realized that both the solute and the solvent are affected by the solvation process, and more useful information is gained when the changes occurring in both are taken into account. 

Instruments with indirect pressure measurement. In this case, the pressure is determined as a function of a pressure-dependent (or more accurately, density-dependent) property (thermal conductivity, ionization probability, electrical conductivity) of the gas. These properties are dependent on the molar mass as well as on the pressure. The pressure reading of the measuring instrument depends on the type of gas. 

The conductance of an electrolyte solution characterizes the easiness of electric conduction its unit is reciprocal ohm, = siemens = S = A/V. The electric conductivity is proportional to the cross-section area and inversely proportional to the length of the conductor. The unit of conductivity is S/m. The conductivity of an electrol3de solution depends on the concentration of the ions. Molar conductivity, denoted as X, is when the concentration of the hypothetical ideal solution is 1 M = 1000 mol/m. Hence, the unit of molar conductivity is either Sm M , or using SI units, Sm mol . For nonideal solutions, X depends on concentration, and the value of X at infinite dilution is denoted by subscript "0" (such as >,+ 0, and X for cation and anion molar conductivity). The conductivity is a directly measurable property. The molar conductivity at infinite dilution may be related to the mobility as follows ... 

With the decrease in permittivity, however, complete dissociation becomes difficult. Some part of the dissolved electrolyte remains undissociated and forms ion-pairs. In low-permittivity solvents, most of the ionic species exist as ion-pairs. Ion-pairs contribute neither ionic strength nor electric conductivity to the solution. Thus, we can detect the formation of ion-pairs by the decrease in molar conductivity, A. In Fig. 2.12, the logarithmic values of ion-association constants (log KA) for tetrabutylammonium picrate (Bu4NPic) and potassium chloride (KC1) are plotted against (1 /er) [38]. 

There are two classes of materials which may be used as electrolytes in all-solid-state cells polymer electrolytes, materials in which metal salts are dissolved in high molar mass coordinating macromolecules or are incorporated in a polymer gel, and ceramic crystalline or vitreous phases which have an electrical conductance wholly due to ionic motion within a lattice structure. The former were described in Chapter 7 in this... 

Fig. 4. The concentration dependence of various electronic properties of metal-ammonia solutions, (a) The ratio of electrical conductivity to the concentration of metal-equivalent conductance, as a function of metal concentration (240 K). [Data from Kraus (111).] (b) The molar spin (O) and static ( ) susceptibilities of sodium-ammonia solutions at 240 K. Data of Hutchison and Pastor (spin, Ref. 98) and Huster (static, Ref. 97), as given in Cohen and Thompson (37). The spin susceptibility is calculated at 240 K for an assembly of noninteracting electrons, including degeneracy when required (37).

A simpler and technologically superior approach is the measurement of the direct electrical conductance. The background conductivity of the mobile phase is electronically subtracted, not requiring a suppressor device. One example of direct conductivity detection is the simultaneous determination of potassium nitrate and sodium monofluorophosphate in dentrifices [76]. Alendronate, a bisphonate, can be directly detected in intravenous solutions and tablets using an anion-exchange column and conductivity detection [77]. Another example, from one of the author s (JA) laboratory is shown in Figure 5.3. Direct conductivity detection makes it possible to selectively detect choline in the presence of an equal molar amount of an antibiotic which is not detected. 

As far as the determination of the composition of the complex is concerned, this can be obtained from the variation of electrical conductance of an ionic solution titrated with a solution of the neutral receptor as a result of the different mobilities of the species in solution. Plots of molar conductances, Am, against the ratio of the concentrations of the receptor and anion can provide useful information regarding the strength of anion-receptor interaction. In fact, several conclusions can be drawn from the shape of the conductometric titration curves. 

The formation of complex ions is an important problem for the study of the structure and properties of molten salts. Several physicochemical measurements give evidence of the presence of complex ions in melts. The most direct methods are the spectroscopic methods which obtain absorption, vibration and nuclear magnetic resonance spectra. Also, the formation of complex ions can be demonstrated, without establishing the quantitative formula of the complexes, by the variation of various physicochemical properties with the composition. These properties are electrical conductivity, viscosity, molecular refraction, diffusion and thermodynamic properties like molar volume, compressibility, heat of mixing, thermodynamic activity, surface tension. 

Equivalent conductivities (and ionic mobilities) of the melts are similar to that of aqueous solutions. Very high specific conductivities are typical for molten salts, as seen in Table 1 [49], The reason for this is the fact that molten salts are very concentrated solutions (for example, the concentration of molten LiF is about 65 molar the concentration of molten KC1 is about 20 molar, etc.). The electrical conductivities of various molten salts cannot be compared at constant temperature because of their different melting points. Therefore, in Table 1 the values of conductivities were selected at 50° above the melting point of each salt. 

Markov et al. [60,61] proposed an equation for the equivalent electrical conductivity of simple binary molten salt mixtures. In binary systems (MjX + M2X or MXj + MX2) there is the possibility of the following ionic arrangements MjX — MjX M2X — M2X MjX — M2X. The probabilities of forming the combinations MjX - MjX M2X - M2X and MjX - M2X are proportional to X, x2 and 2xxx2, respectively, where Xt and x2 are the molar fractions of the two salts. For monovalent molten salts, the equivalent electrical conductivity of a mixture of these salts, Am, can be written as... 

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