Electrical conductivity of ion

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. 

There is a conceptual model of hydrated ions that includes the primary hydration shell as discussed above, secondary hydration sphere consists of water molecules that are hydrogen bonded to those in the primary shell and experience some electrostatic attraction from the central ion. This secondary shell merges with the bulk liquid water. A diagram of the model is shown in Figure 2.3. X-ray diffraction measurements and NMR spectroscopy have revealed only two different environments for water molecules in solution of ions. These are associated with the primary hydration shell and water molecules in the bulk solution. Both methods are subject to deficiencies, because of the generally very rapid exchange of water molecules between various positions around ions and in the bulk liquid. Evidence from studies of the electrical conductivities of ions shows that when ions move under the influence of an electrical gradient they tow with them as many as 40 water molecules, in dilute solutions. 

Important Quantities Connected with Electro Dialysis 3.5.1. Electrical Conductivity of Ion-Exchange Membranes The specific electrical conductivity of an ion selective membrane is given by ... 

Ion-permeable membranes are changing ionic forms during eleclrodialysis. The electrical conductivity of ion-permeable membrane containing two ion species 1 and 2 can be calculated as the average between two extreme values. One of them is based on the model of parallel independent movement of two types of ions /m) and another one is based on the model of successive ion movement from one fixed charge to another [2] ... 

The electric conductivity of ion-exchange membranes increases as temperature rises. This change may be characterized with an equation similar to the Arrhenius equation for viscosity. 

To calculate electron production must be balanced against electron depletion. Free electrons in the gas can become attached to any of a number of species in a combustion gas which have reasonably large electron affinities and which can readily capture electrons to form negative ions. In a combustion gas, such species include OH (1.83 eV), O (1.46 eV), NO2 (3.68 eV), NO (0.09 eV), and others. Because of its relatively high concentration, its abUity to capture electrons, and thus its abUity to reduce the electrical conductivity of the gas, the most important negative ion is usuaUyOH . 

The easy movement of the electrons gives the high electrical conductivity of metals. The metallic bond has no directionality, so that metal ions tend to pack to give simple, high-density structures, like ball-bearings shaken down in a box. 

There is no noticeable tendency for pure N2O4 to dissociate into ions and the electrical conductivity of the liquid is extremely low (1.3 x 10 ohm cm" at 0°). The physical properties of N2O4 are summarized in Table 11.11. 

Despite these reaction products there is little evidence for an ionic self-dissociation equilibrium in liquid CIF3 such as may be formally represented by 2CIF3 V— CIF2 + C1F4, and the electrical conductivity of the pure liquid (p. 828) is only of the order of 10 ohm cm. The structures of these ions are discussed more fully in subsequent sections. 

Chlorides have probably received the most study in relation to their effect on corrosion. Like other ions, they increase the electrical conductivity of the water so that the flow of corrosion currents will be facilitated. They also reduce the effectiveness of natural protective films, which may be permeable to small ions the effect of chloride on stainless steel is an extreme example but a similar effect is noted to a lesser degree with other metals. Turner" has observed that the meringue dezincification of duplex brasses is affected by the chloride/bicarbonate hardness ratio. 

When an ionic solution contains neutral molecules, their presence may be inferred from the osmotic and thermodynamic properties of the solution. In addition there are two important effects that disclose the presence of neutral molecules (1) in many cases the absorption spectrum for visible or ultraviolet light is different for a neutral molecule in solution and for the ions into which it dissociates (2) historically, it has been mainly the electrical conductivity of solutions that has been studied to elucidate the relation between weak and strong electrolytes. For each ionic solution the conductivity problem may be stated as follows in this solution is it true that at any moment every ion responds to the applied field as a free ion, or must we say that a certain fraction of the solute fails to respond to the field as free ions, either because it consists of neutral undissociated molecules, or for some other reason ... 

As an example we may mention an aqueous solution of thallous chloride, T1C1. The radius ascribed to the ion T1+ is a little larger than that of K+, and about equal to that of the rubidium ion Rb+. The electrical conductivity of a dilute solution of T1C1 is not very different from that of KC1 or RbCl, but its variation with the concentration of T1C1 is... 

Incomplete Dissociation into Free Ions. As is well known, there are many substances which behave as a strong electrolyte when dissolved in one solvent, but as a weak electrolyte when dissolved in another solvent. In any solvent the Debye-IIiickel-Onsager theory predicts how the ions of a solute should behave in an applied electric field, if the solute is completely dissociated into free ions. When we wish to survey the electrical conductivity of those solutes which (in certain solvents) behave as weak electrolytes, we have to ask, in each case, the question posed in Sec. 20 in this solution is it true that, at any moment, every ion responds to the applied electric field in the way predicted by the Debye-Hiickel theory, or does a certain fraction of the solute fail to respond to the field in this way In cases where it is true that, at any moment, a certain fraction of the solute fails to contribute to the conductivity, we have to ask the further question is this failure due to the presence of short-range forces of attraction, or can it be due merely to the presence of strong electrostatic forces ... 

Measurements of the electrical conductivities of 0.10 M solutions of these two acids show that there are more ions present in the HF solution than in the acetic acid solution. We can conclude that acetic acid is a weaker acid than HF. This information is conveyed quantitatively in terms of the equilibrium constants for reactions (36) and (37) ... 

Molten lithium fluoride and sodium chloride have easily measured electrical conductivities. Nevertheless, these conductivities are lower than metallic conductivities by several factors of ten. Molten sodium chloride at 750°C has a conductivity about IQ-5 times that of copper metal at room temperature. It is unlikely that the electric charge moves by the same mechanism in molten NaCl as in metallic copper. Experiments show that the charge is carried in molten NaCl by Na+ and Cl- ions. This electrical conductivity of the liquid is one of the most characteristic... 

Electrical methods of analysis (apart from electrogravimetry referred to above) involve the measurement of current, voltage or resistance in relation to the concentration of a certain species in solution. Techniques which can be included under this general heading are (i) voltammetry (measurement of current at a micro-electrode at a specified voltage) (ii) coulometry (measurement of current and time needed to complete an electrochemical reaction or to generate sufficient material to react completely with a specified reagent) (iii) potentiometry (measurement of the potential of an electrode in equilibrium with an ion to be determined) (iv) conductimetry (measurement of the electrical conductivity of a solution). 

The combustion of mixtures of hydrogen and air produces very few ions so that with only the carrier gas and hydrogen burning an essentially constant signal is obtained. When, however, carbon-containing compounds are present ionisation occurs and there is a large increase in the electrical conductivity of the flame. Because the sample is destroyed in the flame a stream-splitting device is employed when further examination of the eluate is necessary this device is inserted between the column and detector and allows the bulk of the sample to by-pass the detector. 

Many types of oxide layers have a certain, not very high electrical conductivity of up to 10 to 10 S/cm. Conduction may be cationic (by ions) or anionic (by or OH ions), or of the mixed ionic and electronic type. Often, charge transport occurs by a semiconductor hole-type mechanism, hence, oxides with ionic and ionic-hole conduction are distinguished (in the same sense as p-type and n-type conduction in the case of semiconductors, but here with anions or cations instead of the electrons, and the corresponding ionic vacancies instead of the electron holes). Electronic conduction is found for the oxide layers on iron group metals and on chromium. 

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