Specific conductances

Specific conductance or electrical conductivity (EC) of a solution (e.g., natural water sample) is a function of total dissolved ions, type of ions, and their potential to form charged or noncharged pairs or complexes. The equation used to predict EC, in units of milimhos per centimeter (mrnhos cm-1), is 

TABLE 2.9. Equivalent look Conductance of Different Ions Found in Natural Water Systems 

Generally, the most commonly encountered ions in natural bodies of water, with the exception of H+ and OH-, exhibit A values in the range of approximately 50-80 cm2 (equiv- 2)-1. Hydrogen and OH- exhibit A values of 349.8 and 198.0 (equiv- 2)-1, respectively. Because H+ and OH-exhibit much greater A values than all other metallic ions, and because ions in solution have a tendency to interact physically with each other (form pairs or complexes), the relationship between solution EC and solution 

Electrical conductivity is one of the most rapid and inexpensive measurements that can be made to assess water quality. It is a common practice to change EC values into milligrams per liter (mg L-1) or parts per million (ppm) of dissolved solids. The equation for doing so is  

Equation 2.73 is only applicable to water samples with EC less than 1 mmhos cm-1. For EC greater than 1 mmhos cm-1, Equation 2.73 gives erroneous results. For example, according to Equation 2.73, a water sample with an EC of 2.3 mmhos cm 1 will have approximately 1472 ppm dissolved solids. If this water sample represented a sulfate water, its actual dissolved solids would be nearly 1900 ppm. For water samples with an EC above 1 mmhos cm-1 Equation 2.74 maybe more applicable. 

FIGURE 4.25 (a) Schematic of soil cation exchange showing the displacement of and NHj by Fe + and 

Mn + ions, (b) Change in the ionic strength of soil solution when influenced by flooding. 

Oxidant is the electron acceptor, and reductant is the electron donor. 

Under standard-state conditions, the relationship between Eh and pH is defined as follows (assuming fi° = 0 V and the ratio of reductant to oxidant as unity)  

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

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

The resistance due to a circular junction is given by / = /2ak, where a is the radius of the junction and k is specific conductivity of the metal. For the case of two steel plates, the measured resistance is 5 x 10" Q for a load of 50 kg the yield pressure of steel is 60 kg/mm, and the specific resistance is 5x 10 Q/cm. Calculate the number of junctions, assuming that it is their combined resistance that is giving the measured value. 

Suppose that the specific conductivities of an oil and a liquid phase are 2 x 10 and 2 x 10 0 cm , respectively. Calculate and plot versus the specific conductivities of O/W and W/0 emulsions formed from these phases. 

Cryoscopic investigations suggest that in sulpholan nitronium tetrafluoroborate exists predominantly as ion pairs. - The specific conductivity of these solutions increases linearly with the concentration of the salt (up to 0-4 mol 1 ), and is attributed to the existence of ion-triplets rather than free ions. ... 

To prepare the standard pH buffer solutions recommended by the National Bureau of Standards (U.S.), the indicated weights of the pure materials in Table 8.15 should be dissolved in water of specific conductivity not greater than 5 micromhos. The tartrate, phthalate, and phosphates can be dried for 2 h at 100°C before use. Potassium tetroxalate and calcium hydroxide need not be dried. Fresh-looking crystals of borax should be used. Before use, excess solid potassium hydrogen tartrate and calcium hydroxide must be removed. Buffer solutions pH 6 or above should be stored in plastic containers and should be protected from carbon doxide with soda-lime traps. The solutions should be replaced within 2 to 3 weeks, or sooner if formation of mold is noticed. A crystal of thymol may be added as a preservative. 

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. 

Specific breakage rate Specific conductivity Specific ion electrode Specific properties... 

The reaction rate is increased by using an entraining agent such as hexane, benzene, toluene, or cyclohexane, depending on the reactant alcohol, to remove the water formed. The concentration of water in the reaction medium can be measured, either by means of the Kad-Eischer reagent, or automatically by specific conductance and used as a control of the rate. The specific electrical conductance of acetic acid containing small amounts of water is given in Table 6. 

Table 6. Specific Conductance of Aqueous Acetic Acid...

The free sulfur trioxide can be titrated with water the end point is deterrnined conductimetricaHy. The sulfuric acid content is deterrnined from the specific conductivity of the Hquid at the point in the titration where no free SO or excess water is present. If the presence of HF is suspected, a known amount of SO is added to the acid and the excess SO is deterrnined as above. The content of another common impurity, SO2, may be determined iodometricaHy in a dilute, aqueous solution. 

Specific Conductance. The specific conductance depends on the total concentration of the dissolved ioni2ed substances, ie, the ionic strength of a water sample. It is an expression of the abiUty of the water to conduct an electric current. Freshly distilled water has a conductance of 0.5—2 ]lS/cm, whereas that of potable water generally is 50—1500 ]lS/cm. The conductivity of a water sample is measured by means of an a-c Wheatstone-bridge circuit with a null indicator and a conductance cell. Each cell has an associated constant which, when multiphed by the conductance, yields the specific conductance. 

The concentration of dissolved ionic substances can be roughly estimated by multiplying the specific conductance by an empirical factor of 0.55—0.9, depending on temperature and soluble components. Since specific conductance is temperature dependent, all samples should be measured at the same temperature. Alternatively, an appropriate temperature-correction factor obtained by comparisons with known concentrations of potassium chloride may be used. Instmments are available that automatically correct conductance measurements for different temperatures. 

Quantitative Relationship of Conductivity and Antistatic Action. Assuming that an antistatic finish forms a continuous layer, the conductance it contributes to the fiber is proportional to the volume or weight and specific conductance of the finish. As long as the assumption of continuity is fulfilled it does not matter whether the finish surrounds fine or coarse fibers. Assuming a cylindrical filament of length 1 cm and radius r, denoting the thickness of the finish layer as Ar and the specific conductance of the finish k, the conductance R of the finish layer is given by the equation (84) ... 

The specific conductance of the finish on the filament k is not necessarily the specific conductance it exhibits in its bulk condition. For instance, absorption of ions from the finish by the fiber can reduce the conductivity. The specific conductance greatiy depends on the amount of moisture present. Figure 4a shows the experimentally observed resistance of yam as a function of the amount of antistatic agent appHed in comparison to the calculated resistance. Below 0.05% of antistatic agent the experimental values show a lower conductivity than calculated this may be due to a lack of continuity of the antistatic agent. 

Materials are usually classified according to the specific conductivity mode, eg, as insulators, which have low conductivity and low mobihty of carriers. Metahic conductors, which include some oxides, have a high conductivity value which is not a strong (exponential) function of temperature. Semiconductors are intermediate and have an exponential temperature dependence. Figure 1 gives examples of electrical conductivities at room temperature for these various materials. 

Physical Properties. Most of the physical properties discussed herein depend on the direction of measurement as compared to the bedding plane of the coal. Additionally, these properties vary according to the history of the piece of coal. Properties also vary between pieces because of coal s britde nature and the crack and pore stmcture. One example concerns electrical conductivity. Absolute values of coal sample specific conductivity are not easy to determine. A more characteristic value is the energy gap for transfer of electrons between molecules, which is deterrnined by a series of measurements over a range of temperatures and is unaffected by the presence of cracks. The velocity of sound is also dependent on continuity in the coal. 

Sodium chloride and sodium cyanide are isomorphous and form an unintermpted series of mixed crystals. The ferrocyanide ion has a marked effect on the habit of sodium cyanide crystallized from aqueous solution (50). Sodium cyanide and sodium carbonate form a molten eutectic at approximately 53 wt % sodium carbonate and 465°C. The specific conductivity of molten 98% sodium cyanide is 1.17 S /cm (51). 

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