Electrical conductivity of salts

E5.10 Electric Conductivity of Salt Crystals, Melts and Solutions... 

Arrhenius, Svante August won the 1903 Nobel Prize in Chemistry for his work on the electrical conductivity of salt solutions (he was also nominated for the Physics Prize). He is often hailed as a pioneer of modern environmentalism for his work on the greenhouse effect. One of his predictions was that the United States might pump its last barrel of oil in 1935. Fortunately he was proved wrong, but his concern about the world s natural mineral resources and the need for alternative sources of energy was prescient. He died in 1927 at age 68. 

The British scientist Henry Cavendish (1731-1810) reported that the electric conductivity of water is greatly increased by dissolving salt in it. In 1884 the young Swedish scientist Svante Arrhenius (1859-1927) published his doctor s dissertation, which included measurements of the electric conductivity of salt solutions and his ideas as to their interpretation. These ideas were rather vague, but he later made them more precise and then published a detailed paper on ionic dissociation in 1887. Arrhenius assumed that in a solution of sodium chloride in water there are present sodium ions, Na, and chloride ions, Cl . When electrodes are put into such a solution the sodium ions are attracted toward the cathode and move in that direction, and the chloride ions are attracted toward the anode and move in the direction of the anode. The motion of these ions through the solution, in opposite directions, provides the mechanism of conduction of the current of electricity by the solution. 

Alkali and Alkaline Earth Metal Production by Molten Salt Electrolysis, Fig. 4 Specific electrical conductivity of salt rich mixtures of NaCl-Na and KCl-K from Bredig [5]... 

It is believed that to avoid any risk of explosion, the electrical conductivity of jet fuel should fall between 50 and 450 pS/m. This level is attained using anti-static additives which are metallic salts (chromium, calcium) added at very low levels on the order of 1 ppm. 

As early as 1889 Walker (320), using samples of thiazole, 2,4-dimethylthiazoie, pyridine, and 2,6-dimethylpyridine obtained from Hantzsch s laboratory, measured the electrical conductivity of their chlorhydrates and compared them with those of salts of other weak bases, especially quinoline and 2-methylquinoline. He observed the following order of decreasing proton affinity (basicity) quinaldine>2,6-dimethyl-pyridine>quinoline>pyridine>2,4-dimethylthiazole> thiazole, and concluded that the replacement of a nuclear H-atom by a methyl group enhanced the basicity of the aza-aromatic substrates. 

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

Table 2. Comparative Electrical Conductivity of Lithium Salts...

The salt content determines the specific electrical conductivity of the water (see Section 2.2.2). In coastal areas this varies according to tide and time of year. The following average values in ohms per centimeter serve as a guide Narvik roadstead, 33 [7] Helgoland, 27 [7] North Sea, 30 Elbe/Cuxhaven, 100 [7] Elbe/ Brunsbuttelkoog, 580 Elbe/Altona, 1200 Liibeck wharf, 75 Antwerp (Quay 271), 120 Rotterdam Botlek, 240 Tokyo Gulf, 25 [8]. 

Arrhenius, insofar as his profession could be defined at all, began as a physicist. He worked with a physics professor in Stockholm and presented a thesis on the electrical conductivities of aqueous solutions of salts. A recent biography (Crawford 1996) presents in detail the humiliating treatment of Arrhenius by his sceptical examiners in 1884, which nearly put an end to his scientific career he was not adjudged fit for a university career. He was not the last innovator to have trouble with examiners. Yet, a bare 19 years later, in 1903, he received the Nobel Prize for Chemistry. It shows the unusual attitude of this founder of physical chemistry that he was distinctly surprised not to receive the Physics Prize, because he thought of himself as a physicist. 

The effect of water salinity on crop growth is largely of osmotic nature. Osmotic pressure is related to the total salt concentration rather than the concentration of individual ionic elements. Salinity is commonly expressed as the electric conductivity of the irrigation water. Salt concentration can be determined by Total Dissolved Solids (TDS) or by Electrical Conductivity (EC). Under a water scarcity condition, salt tolerance of agricultural crops will be the primordial parameter when the quality of irrigation water is implicated for the integrated water resources management [10]. 

Lithium triflate was the most used salt and the temperature dependence of the electrical conductivity of a series of (LiS03CF3)x/MEEP complexes with a ratio metal cation/MEEP repeat unit 0.125[Pg.203]

The complete dissociation of the hydrocarbons [l 2 ], [28" 2 ] and [40" 2 ] in DMSO has been demonstrated by quantitative generation of both Kuhn s carbanion [2 ] and carbocations [1" ], [28" ] and [40" ] as determined by UV-vis spectra (Table 6 and Eig. 4). However, since carbocation [24 ] has no absorptions at a wavelength region longer than 220 nm in the UV spectrum, there remained an ambiguity that this cation might have decomposed in the DMSO solution. A clue to this problem could be obtained by determination of the electric conductivity of DMSO solutions of hydrocarbon salts (Table 7) (Okamoto et al., 1990). 

The composition of the electrolyte is quite important in controlling the electrolytic deposition of the pertinent metal, the chemical interaction of the deposit with the electrolyte, and the electrical conductivity of the electrolyte. In the case of molten salts, the solvent cations and the solvent anions influence the electrodeposition process through the formation of complexes. The stability of these complexes determines the extent of the reversibility of the overall electroreduction process and, hence, the type of the deposit formed. By selecting a suitable mixture of solvent cations to produce a chemically stable solution with strong solute cation-anion interactions, it is possible to optimize the stability of the complexes so as to obtain the best deposition kinetics. In the case of refractory and reactive metals, the presence of a reasonably stable complex is necessary in order to yield a coherent deposition rather than a dendritic type of deposition. 

Arrhenius postulated in 1887 that an appreciable fraction of electrolyte in water dissociates to free ions, which are responsible for the electrical conductance of its aqueous solution. Later Kohlrausch plotted the equivalent conductivities of an electrolyte at a constant temperature against the square root of its concentration he found a slow linear increase of A with increasing dilution for so-called strong electrolytes (salts), but a tangential increase for weak electrolytes (weak acids and bases). Hence the equivalent conductivity of an electrolyte reaches a limiting value at infinite dilution, defined as... 

Poly[(aniline-2-chloroaniline)-4-toluenesulfonic acid salt] was obtained by oxidative copolymerization of aniline with 2-chloroaniline in solutions containing 4-toluenesulfonic acid. The copolymer salt was subjected to heat treatment under nitrogen atmosphere at elevated (about 150°C) temperatures. The heat-treated samples acquired electric conductivity of 2.7 X 10 f2 cm . According to ESR spectra, the heated poly[(aniline-2-chloroaniline)-4-toluenesulfonic salt] exists as the poly(semiquinone imine ion-radical) in which unpaired electrons are localized on or near the nitrogen atoms (Palaniappan 1997). 

All these data verify that in real systems, the rate of electron transfer between components of a conductive chain is high. There are states of a mixed valence. Enhanced electric conductivity and other unusual physical properties are widespread among those inorganic or coordination compounds that contain metals in intermediate -valence states. In cases of organic metals, nonstoi-chiometric donor/acceptor ratios provide even better results. For example, the salt of (TTF)i (Br)oj composition displays an electric conductivity of 2 X 10 cm while (TTF)i(Br)i salt does not... 

Electric conductivity of ion-radical salts arises from the mobility of their unpaired electrons. At the same time, each of the unpaired electrons possesses a magnetic moment. This small magnetic moment is associated with the electron quantum-mechanical spin. Spin-originated magnetism as a phenomenon is described in many sources (see, e.g., monographs by Khan 1993, Bauld 1997, Itokh and Kinoshita 2001 and reviews by Miller 2000, Miller and Epstein 1994, 1995, Wudl and Thompson 1992). This section is, naturally, devoted to the organic magnets based on ion-radicals. 

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