Conductance, electrolytic equivalent

As in the case of solutions, the specific conductance, K, the equivalent conductance, a, and the molar conductance, am, are also distinguished for molten electrolytes. These are defined in the same manner as done for the case of solutions of electrolytes. It may, however, be pointed out that molten salts generally have much higher conductivities than equivalent aqueous systems. 

In fact, the conductivity k can be thought of as the conductance of 1 cm3 of the electrolyte solution. Now, let us suppose that 1 cm3 would contain 1 g-equiv. of electrolyte and let us call its conductivity the equivalent conductivity, A, then the relation... 

As an example of this, consider the three compounds obtained from hexammino-eobaltie chloride by replacing ammonia by nitrito-groups. The same total number of acidic radicles is retained in the molecule, but the derivatives differ in electrical conductivity in equivalent solutions. The molecular conductivity of hexammino-eobaltie chloride at 25° C. and 1000 litres dilution is 431-6 of the mononitrito-derivative, [Co(NH3)5(N02)]C12, is 246-4 of the di-derivative, [Co(NH3)4(N02)2]C1, is 98-83 and of the trinitrito-derivative, [Co(NH3)3(N02)3], is zero, this being a non-electrolyte. Further substitution transforms the complex from cation to anion thus [Co(NH3).2(N02)4]K. 

To a first approximation, the BLM can be considered to behave like a parallel plate capacitor immersed in a conducting electrolyte solution. In reality, even such a thin insulator as the modified BLM (designated by and R, in Fig. 108) could block the specific adsorption of some species from solution and/or modify the electrochemical behavior of the system. Similarly, System C may turn out to be a semiconductor(l)-insulator-semiconductor(2) (SIS ) rather than a semiconductor(l)-semiconductor(2) (SS ) junction. The obtained data, however, did not allow for an unambiguous distinction between these two alternative junctions we have chosen the simpler of the two [652], The equivalent circuit describing the working (Ew), the reference (Eg), and the counter (Ec) electrodes the resistance (Rm) and the capacitance (C of the BLM the resistance (R ) and capacitance (Ch) of the Helmholtz electrical double layer surrounding the BLM as well as the resistance of the electrolyte solution (RSO ) is shown in Fig. 108a [652],... 

Unlike specific conductance the equivalent conductance of both strong and weak electrolytes drops with increasing concentration and increases with decreasing concentration up to a certain limit value A° (see Table 4 and Fig. 5). 

Electrolyte conductivity depends on three factors the ion charges, mobilities, and concentrations of ionic species present. First, the number of electrons each ion carries is important, because A, for example, carries twice as much charge as A . Second, the speed with which each ion can travel is termed its mobility. The mobility of an ion is the limiting velocity of the ion in an electric field of unit strength. Factors that affect the mobility of the ion include (1) the solvent (e.g., water or organic), (2) the applied voltage, (3) the size of the ion (the larger it is, the less mobile it will be), and (4) the nature of the ion (if it becomes hydrated, its effective size is increased). The mobility is also affected by the viscosity and temperature of the solvent. Under standard conditions the mobility is a reproducible physical property of the ion. Because in electrolytes the ion concentration is an important variable, it is usual to relate the electrolytic conductivity to equivalent conductivity. This is defined by... 

Equivalent and molar conductivities are commonly used to express the conductivity of the electrolyte. Equivalent conductance depends on the concentration of the solution. If the solution is a strong electrolyte, it will completely dissociate the components in the solution to ionic forms. Kohlrauch (Macinnes, 1939) found that the equivalent conductance of a strong electrolyte was proportional to the square root of its concentration. However, if the solution is a weak electrolyte which does not completely dissociate the components in the solution to respective ions, the above observation by Kohlrauch is not applicable. 

FIGURE 10.10 PEDT as cathode material (grey = metal white = metal oxide dielectric black = PEDT layer), boosting performance of solid electrolytic capacitors by better conductivity, lower equivalent series resistance (ESR), better impregnation, and avoidance of ignition. 

The complex impedance plots of these electrolytes recorded at frequencies between 5 Hz and 100 kHz consist of a single spur touching down at the real axis (Figure 3.8). The spectrum corresponds to an equivalent circuit in which a resistor is in series with a capacitor and is consistent with the arguments developed earlier in this chapter for the impedance spectrum of a highly conductive electrolyte in this frequency range. 

Figure 22. Simplified electronic equivalent circuit (measured is / B = bull membrane resistance) and impedance spectra of the real part (admittance) in a 1 M Ca(N03>2 ( ) supporting electrolyte and increasing concentrations with a valino-mycin-based potassium conductometric microsensor. Note that even pM amounts of ions in a well conducting electrolyte solution can be sensed...

In some compounds, a large number of ions are in a disordered state because of many structural defects, leading to so-called "structural disorder." The ions "hop" from one position to another, allowing ionic conduction to take place. When the activation energy for the ion hopping is low, the ionic conductivity is equivalent to that of liquid electrolytes. 

See chemical equivalent, equivalent conductivity The specific conductance multiplied by the volume (ml) which contains 1 g equivalent of the electrolyte. 

Table 8.35 Equivalent Conductivities of Electrolytes in Aqueous Solutions at...

The equivalent conductivity of an electrolyte is the sum of contributions of the individual ions. At infinite dilution A° = A° -f A, where A° and A are the ionic conductances of cations and anions, respectively, at infinite dilution (Table 8.35). 

The term equivalent conductance A is often used to describe the conductivity of electrolytes. It is defined as the conductivity of a cube of solution having a cross-section of one square centimeter and containing one equivalent of dissolved electrolyte. 

Figure 16.1 Simple dry cell battery. Electrons are conducted along the external circuit (4), which physically connects the active (2) and noble (1) materials. An equivalent ionic counter-current is conducted through the electrolyte (3), thereby completing the circuit.

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

Weak acids with weak bases. The titration of a weak acid and a weak base can be readily carried out, and frequently it is preferable to employ this procedure rather than use a strong base. Curve (c) in Fig. 13.2 is the titration curve of 0.003 M acetic acid with 0.0973 M aqueous ammonia solution. The neutralisation curve up to the equivalence point is similar to that obtained with sodium hydroxide solution, since both sodium and ammonium acetates are strong electrolytes after the equivalence point an excess of aqueous ammonia solution has little effect upon the conductance, as its dissociation is depressed by the ammonium salt present in the solution. The advantages over the use of strong alkali are that the end point is easier to detect, and in dilute solution the influence of carbon dioxide may be neglected. 

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