Measurement of Electrical Conductivity

In an excess of nitric acid, nitrous acid exists essentially as dinitrogen tetroxide which, in anhydrous nitric acid, is almost completely ionised. This is shown by measurements of electrical conductivity, and Raman and infra-red spectroscopy identify the ionic species... 

According to Dobbie et the ultraviolet spectrum of cotarnine in dilute aqueous or alcoholic solution is identical with that of cotarnine chloride [(1), Ch instead of OH"], but in nonpolar solvents it is identical with that of hydrocotarnine (10a), 1-ethoxy-hydrocotarnine (10b), and cotarnine pseudocyanide (10c). This is in agreement with Decker s view of the structure of cotarnine and with the conclusions of Hantzsch and Kalb. Measurement of electrical conductivity in-... 

The determination of the degree of dissociation of cotarnine ° and the good agreement with the values derived from measurements of electrical conductivity with those from the spectrophotometric methods is indirect evidence that no significant part of the undissociated cotarnine is in the amino-aldehyde form. In the conductance calculation, the undissociated part was neglected. If this included a significant amount of amino-aldehyde (i.e., a secondary base), there would be a noticeable discrepancy in the degree of dissociation obtained by the two methods. 

The phenomenon of transmitting electrons through a body (an electric current). Usually associated with the measurement of electrical conductivity through water and measured in micro Siemens per centimeter (p,S/cm) or micromho per centimeter ( xmho/cm). 1 p,S/cm = 1 xmho/cm. The mho is equivalent to a reciprocal ohm (the unit of resistivity). 

Measurements of electrical conductivity permit the identification of the charge-carrying species in the solid phase and also the detection of ionic melts [111,417]. Bradley and Greene [418], for example, could determine the kinetics of reactions between Agl, KI and Rbl because the product (K, Rb)Ag4Is had a considerably higher conductivity than the reactants. The conductivity of the reactant mixture was proportional to the thickness of the product layer. 

An aqueous solution of a molecular substance such as sugar (C12 H22 Oi 1) or ethanol (C2 H5 OH) contains individual molecules in a sea of water molecules (Figure 3-181. We know that these solutes dissolve as neutral molecules from measurements of electrical conductivity. Figure 3-19 shows that pure water does not conduct electricity, and neither does a solution of sugar in water. This result shows that these solutions contain no mobile charged particles. Sugar and ethanol dissolve as neutral molecules. 

The conclusion regarding the fact that constant current conductivity involves not all microcrystals of the sample is proved by results of measurements of electric conductivity in sintered ZnO films in case of alternating current (Fig. 2.10). The availability of barrier-free ohmic pathways is proved by a low value of initial resistivity in sintered samples ( 1 - 5 kOhm) in addition to exponential dependence of electric conductivity plotted as a function of inverse temperature having activation energy 0.03 - 0.5 eV, which coincides with ionization energy of shallow dope levels. The same value is obtained from measurements of the temperature dependence of the Hall constant [46]. 

Preliminary measurements of electrical conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10 °S/cm which apparently is not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase in conductivity. Ongoing studies of the electrical properties of these conjugated polymers with alternating aromatic/quinonoid units will be reported elsewhere. 

The experimental determination of RBA, however, is difficult but some attempts have been made and these include direct observation, measurements of electrical conductivity, shrinkage energy, gas adsorption and light scattering. The linear elastic response of paper has been explained in terms of various micromechanical models which take into account both fibre and network properties, including RBA. An example of one which predicts the sheet modulus, Es is given below ... 

Strictly, there is no direct evidence concerning the presence of ions for any aliphatic hydrocarbon monomers. The spectroscopic studies which are of such great diagnostic value for aromatic systems are at present useless for those involving aliphatic monomers and therefore such information as we have for these (Table 3) consists of measurements of electrical conductivity and other, more circumstantial, evidence. It is not claimed that the evidence assembled in these Tables is complete and as far as Table 3, especially, is concerned, its content depends obviously on what one considers to be satisfactory evidence for the participation of ions. 

At the 4thONRSympDeton (Ref 13) B. Hayes, pp 595-601, reported further progress in the measurement of electrical conductivity behind the detonation front. He had succeeded in his final goal, the measurement of reaction zone structure, thru an improvement in time resolution, from a few tenths of a microsecond to a few tenths of a nanosecond. 

Unlike direct measurements of electrical conductivity of DNA [34, 35], chemical and photochemical experiments provide detailed data on how the CT efficiency depends on the DNA sequence and the local structure of an oligomer [5-9]. The latter experiments rely on intercalated or covalently bound chromophores which may affect the DNA structure. In the following, we will not discuss this effect of the chromophore although we realize that it may be important for a complete description of the systems used in those experiments. Rather, we will focus on a better understanding of the CT through unperturbed DNA fragments. 

In the field of nonmetallic catalysts, particularly of oxides, Hauffe and co-workers (14a) used only semiconductors for which information concerning electronic and ion defects was available from measurements of electrical conductivity, thermoelectric properties, and Hall effect. These workers obtain a quantitative correlation between the reaction rate, the amount of chemisorption, and the number of electron defects of the catalysts. Since every catalyzed reaction is initiated by a chemisorption process involving one or several of the reacting gases, and because the nature of this chemisorption process determines the subsequent steps of the reaction, it seems appropriate to begin with a discussion of the mechanism of chemisorption. 

The best-developed way to measure the association of ions is through the measurement of electrical conductance of dilute solutions. As mentioned, this realization occurred in the nineteenth century to Arrhenius and Ostwald. An elaborate development of conductance equations suitable to a range of ion concentrations of millimolar and lower by many authors (see Refs. 5, 33 and 34 for critical reviews) has made the determination of association constants common. Unfortunately, in dealing with solutions this dilute, the presence of impurities becomes very difficult to control and experimenters should exercise due caution, since this has been the source of many incorrect results. For example, 20 ppm water corresponds to 1 mM water in PC solution, so the effect of even small contaminants can be profound, especially if they upset the acid-base chemistry of association. The interpretation of these conductance measurements leads, by least squares analysis of the measurements, to a determination of the equivalent conductance at infinite dilution, Ao, the association constant for a positively and negatively charged ion pair, KA, and a distance of close approach, d, using a conductance equation of choice. One alternative is to choose the Bjerrum parameter for the distance, which is defined by... 

Analogous results have been reported from the systematic measurements of electrical conductivity and transference numbers of ions (// and tf) in black foam films [336] and parallel measurements of these quantities in highly concentrated surfactant/water system [337], Furthermore, it has been found that while the electrical conductivity of CBF depends on the electrolyte concentration in the initial solution, that of NBF does not. The transference numbers of the ions measured for films and a gel obtained from NaDoS-NaCl-HCl system are given below... 

In ionic polymerizations, the fraction of free ions and of both solvent-separated and contact ions pairs is determined spectrophotometrically by the measurement of electrical conductivity and by NMR chemical shifts. 

Molecular weight regulator. tert-Dodecyl mercaptan (t-DlBK/), purpled py double distillation in vacuum used in polymerization experiments acc[Pg.64]

The frequency of 1000 s" has been mentioned because it is typical for measurement of electrical conductivity. To perform the measurement, theresearcha- varies the frequency (v) and plots the corresponding measured resistance values against l/w, extrapolating the measured resistance in the ordinate to infinite frequency. ... 

The duration of the induction period seems to be independent of the method of observation, whether by direct visual observation, more sensitive optical means, or measurement of electrical conductance. In addition, the conductivity remains nearly constant during the induction period, indicating that during this period oifiy a small fraction of the solute exists as ion pairs or higher aggregates. 

Fig. 18. Basic Wheatstone bridge circuit for the measurement of electrical conductivity.

There are two main ways in which the mirror technique has been applied. In the first, the concentration of radicals is determined by following the rate of mirror removal by one of a number of methods. These include determination of mirror opacity, change in radioactivity from a radioactive mirror, measurement of electrical conductivity, and so on. In the other method, the products formed by the removal of the mirrors are characterized, thus giving an indication of both the nature and concentration of the radicals concerned. Thus Paneth and Hofeditz ... 

Structural studies in fused salts by means of careful and thorough high-temperature measurements of electrical conductivity, density, viscosity, and laser- Raman spectroscopy have been reviewed. Four problem areas are discussed (1) melting mechanisms of ionic compounds with large polyatomic cations, (2) salts as ultra-concentrated electrolyte solutions, (3) structural aspects and Raman spectroscopy, and (4) electrolysis of molten carbonates. The results in these areas are summarized and significant contributions to new experimental techniques for molten-salt studies are discussed.275 The physical properties and structure of molten salts have also been reviewed in terms of operational (hole, free volume, partly disordered crystal) and a priori (intermolecular potential) models.276 Electrochemistry... 

---