Conductivity, electrolytic

The electrolytic conductance of dilute aqueous solutions can often be measured with high precision and thus afford a useful means of determining concentration (see section 3.6.3). A detailed account of the methods used in this area is given by Robinson and Stokes (1970). 

In the author s experience, however, conductivity measurements are of limited use in crystallization work because of the unreliability of measurement in near-saturated or supersaturated solutions. The temperature dependence of electrical conductivity usually demands a very high precision of temperature control. Torgesen and Horton (1963) successfully operated conductance cells for the control of ADP crystallization, but they had to control the temperature to 0.002 °C. 

Good electrical conductance is one of the characteristics of many though not all molten salts. This characteristic has often been employed industrially. Various models have been proposed for the mechanism of electrical conductance. Electrolytic conductivity is related to the structure, although structure and thermodynamic properties are not the main subjects of this chapter. Electrolytic conductivities of various metal chlorides at the melting points are given in Table 4 together with some other related properties.  

Notes Tm, melting point AS, entropy change on melting K, elecholytic conductivity T, shear viscosity. Chemical scale of element proposed by Pettifor.  

The terms specifie conductivity and equivalent conductivity were previously used. However, these terms are not recommended for use as the SI units. They should be replaced by molar conductivity according to the SI recommendation, which states as follows, When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. Thus, when we previously used equivalent conductivity, we should now use molar conductivity, where we define the molar unit so that it is equal to the equivalent unit previously used. For example, we define (l/2)Ca, (l/3)La, (l/2)CO and Alj/jF as molar units. 

Electrolytic conductivity has also been measured in many binary systems. Although data on conductivities in binary mixtures are very useful for practical purposes, the information from such data alone is limited from the viewpoint of elucidation of the mechanism. For example, the empirical Markov rule is well known for the electrical conductivity of binary mixtures. However, many examples have been presented where this rule does not hold well. 

---

Mott N F and M J Littleton 1938. Conduction in Polar Crystals. I. Electrolytic Conduction in Solid Salts. Transactions of the Faraday Society 34 485-499. 

Conductivity. The standard unit of conductance is electrolytic conductivity (formerly called specific conductance) k, which is defined as the reciprocal of the resistance of a 1-m cube of liquid at a specified temperature m— ]. See Table 8.33 and the definition of the cell constant. 

The means by which high current densities are obtained can be understood from an examination of the electrolyte conductivity and the interelectrode gap width. These parameters are related to the current through Ohm s law, which states that the current I fiowing in a conductor of resistance Ris directly proportional to the appHed voltage IN... 

If equations 2 and 3 are combined, relationships between the average current density J, current I, surface area to be machined A, appHed potential difference, gap width h, and electrolyte conductivity are... 

If the increase with temperature of the electrolyte conductivity is neglected, integration of equation 5 yields... 

R. M. Fuoss and F. Accasciua, Electrolytic Conductance, Interscience PubHshers, New York, 1959. 

The characteristics for aqueous KOH (97—99) solutions vary somewhat for battery electrolytes when additives are used. Furthermore, potassium hydroxide reacts with many organics and with the carbon dioxide in air to form carbonates. The build-up of carbonates in the electrolyte is to be avoided because carbonates reduce electrolyte conductivity and electrode activity in some cases. 

Current efficiency depends on operating characteristics, eg, pH, temperature, and cell design, and is generally in the 90—98% range. The cell voltage is a function of electrode characteristics and electrolyte conductivity and can be expressed as... 

Reference electrodes are used in the measurement of potential [see the explanation to Eq. (2-1)]. A reference electrode is usually a metal/metal ion electrode. The electrolyte surrounding it is in electrolytically conducting contact via a diaphragm with the medium in which the object to be measured is situated. In most cases concentrated or saturated salt solutions are present in reference electrodes so that ions diffuse through the diaphragm into the medium. As a consequence, a diffusion potential arises at the diaphragm that is not taken into account in Eq. (2-1) and represents an error in the potential measurement. It is important that diffusion potentials be as small as possible or the same in the comparison of potential values. Table 3-1 provides information on reference electrodes. 

Buried steel pipelines for the transport of gases (at pressures >4 bars) and of crude oil, brine and chemical products must be cathodically protected against corrosion according to technical regulations [1-4], The cathodic protection process is also used to improve the operational safety and economics of gas distribution networks and in long-distance steel pipelines for water and heat distribution. Special measures are necessary in the region of insulated connections in pipelines that transport electrolytically conducting media. 

Nearly all dc railways use the rails to return the operating current. The rails are mounted on wood or concrete sleepers (ties) and have a reasonably good contact with the soil in surface railway installations. The electrolytically conducting soil is... 

In this chapter some important equations for corrosion protection are derived which are relevant to the stationary electric fields present in electrolytically conducting media such as soil or aqueous solutions. Detailed mathematical derivations can be found in the technical literature on problems of grounding [1-5]. The equations are also applicable to low frequencies in limited areas, provided no noticeable current displacement is caused by the electromagnetic field. 

The ions move between electrodes in the electrolyte due to voltage potential gradients. The velocity of these chemical currents increases with temperature. Hence, electrolytic conductivity increases as temperature goes up. This is the opposite of electrical currents m metallic conductors, which increase as the temperature goes down. 

Measurement of conductivity The measurement of electrolyte conductivity — the reciprocal of the resistivity —is a fairly simple matter, being calculated from the resistivity as measured by some of the methods described above. 

Complete and Incomplete Ionic Dissociation. Brownian Motion in Liquids. The Mechanism of Electrical Conduction. Electrolytic Conduction. The Structure of Ice and Water. The Mutual Potential Energy of Dipoles. Substitutional and Interstitial Solutions. Diffusion in Liquids. 

The Mechanism of Electrical Conduction. Let us first give some description of electrical conduction in terms of this random motion that must exist in the absence of an electric field. Since in electrolytic conduction the drift of ions of either sign is quite similar to the drift of electrons in metallic conduction, we may first briefly discuss the latter, where we have to deal with only one species of moving particle. Consider, for example, a metallic bar whose cross section is 1 cm2, and along which a small steady uniform electric current is flowing, because of the presence of a weak electric field along the axis of the bar. Let the bar be vertical and in Fig. 16 let AB represent any plane perpendicular to the axis of the bar, that is to say, perpendicular to the direction of the cuirent. 

Electrolytic Conduction. The same treatment is easily applied to ionic conduction, if the plane AB in Fig. 1C is taken to be a plane in an electrolytic conductor, similar to the electronic conductor discussed above. In the absence of a field the number of negative ions which cross AB in unit time in one direction will not differ appreciably from the number that cross AB in the reverse direction and, treating the positive ions separately, we may make the same remark about the positive ions. 

Electrolytic conduction, 220, see also Conductivity, electrical Electrometer, 75 Electron, 77 affinity, 280... 

The main problem in the study of the role of these parameters in electrolyte conductivity is their interdependence. A change in composition of a binary solvent changes viscosity, along with the permittivity, ion-ion association, and ion solvation, which may be preferential for one of the two solvents and therefore also changes the Stokes radii of the ions. 

---