Sodium chloride equivalent conductance

FIG. 1 Equivalent conductance (A) for sodium chloride (O), sodium acetate (O), and sodium propionate ( ) at 20°C against the square root of solute concentration (v/cb), as extracted from Fidaleo and Moresi (2005a,b, 2006). The continuous lines were calculated using Eq. 4 and the empirical parameters A0 and ft extracted from Fidaleo and Moresi (2005a,b, 2006). 

The value of A° of a given electrolyte can also be determined using equivalent conductances of other electrolytes with either identical cation or anion. So for instance the equivalent conductance of acetic acid can be determined if we add A° of hydrochloric acid and A0 of sodium acetate and substract A° of sodium chloride ... 

Shabanov et al. [54,55] found that the electrical conductivity of the molten alkali chlorides and their binary mixtures is dependent on the strength of the applied electrical field. Figure 7 illustrates the increase of the equivalent electrical conductivity of molten sodium chloride with the strength of the applied electric field, reaching a limiting value of A° at E° 106 V/m. This phenomenon was observed at several temperatures. The increase of the electrical conductivity with... 

A 0.2 iV solution of sodium chloride was found to have a specific conductivity of 1.75 X 10 cm" at 18 °C the transport number of the cation in this solution is 0.385. Calculate the equivalent conductance of the sodium and chloride ions. (Constantinescu)... 

The self-diffusion coefficients of CF and Na" in molten sodium chloride are, respectively, 33 x 10 exp(-8500// 7) and 8x10 exp(-4000// 7) cm s". (a) Use the Nernst-Einstein equation to calculate the equivalent conductivity of the molten liquid at 935°C. (b) Compare the value obtained with the value actually measured, 40% less. Insofar as the two values are significantly different, explain this by some kind of structural hypothesis. 

Use the data in Tables X and XIII to estimate the equivalent conductance of 0.1 N sodium chloride, 0.01 N barium nitrate and 0.001 n magnesium sulfate at 25 . (Compare the results with the values in Table VUI.)... 

A 0.01 N solution of hydrochloric acid (A = 412.0) was placed in a cell having a constant of 10.35 cm." , and titrated with a more concentrated solution of sodium hydroxide. Assuming the equivalent conductance of each electrolyte to depend only on the total ionic concentration of the solution, plot the variation of the cell conductance resulting from the addition of 25, 50, 75, 100, 125 and 150 per cent of the amount of sodium hydroxide required for complete neutralization. The equivalent conductance of the sodium chloride may be taken as 118.5 ohms" cm. the change in volume of the solution during titration may be neglected. 

Saxton and Waters [J. Am. Chem. Soc., 59, 1048 (1937)] gave the ensuing expressions for the equivalent conductances in water at 25 of hydrochloric acid, sodium chloride and sodium a-crotonate (Naa-C.) ... 

Since the ion conductance of the chloride ion is now known accurately, that of the hydrogen, lithium, sodium, potassium and other cations can be derived by subtraction from the equivalent conductances at infinite dilution of the corresponding chloride solutions from these results the values for other anions, and hence for further cations, can be obtained. The data recorded in Table XIII, page 56, were calculated in this manner. 

A solution contains 0.04 n sodium chloride, 0.02 n hydrochloric acid and 0.04 n potassium sulfate calculate, approximately, the fraction of the current carried by each of the ionic species, Na, K" ", H+, Cl and SOr, in this solution. Utilize the data in Tables X and XIII, and assume that the conductance of each ion is the same as in a solution of concentration equal to the total equivalent concentration of the given solution. 

A more typical ion to detect might be chloride. The equivalent conductance is higher so a higher signal would result from this ion, assuming the same peak width and the same sodium counterion. If hydronium ion rather than sodium is the counterion to chloride, then the signal will be multiplied by another factor of 3.4. 

Table II. Observed and Computed Values of the Equivalent Conductance of Potassium and Sodium Chlorides in Water at 25° C.

The following method for computing Ae will make this conception clear. As an example the value of A for acetic acid as a function of the ion concentration will be obtained. The computation depends upon two assumptions the evidence for which has been considered in this chapter. The assumptions are (a) aqueous solutions of sodium chloride, sodium acetate and hydrochloric acid are completely dissociated, and (6) at low ion concentrations the equivalent conductance, X, of the ion constituents of strong electrolytes are independent of the nature of the associated ions, i.ethey follow Kohlrausch s law of independent ion migration. Thus if completely dissociated acetic acid were capable of existence the value of its equivalent conductance Afl hac would be in accord with the relation 20 21-22... 

Equivalent conductivities were first measured of the systems containing 0.014 and 0.025 wt% surfactant (0.35 and 0.62 mM) to shed light on why they threw precipitates months after they had been prepared, tested, and classified as single-phase. The results at these and higher concentrations are given in Figure 5, where data for sodium dodecyl sulfate (28) (which were confirmed to within 10% at low concentrations, 5% at concentrations higher than 5 mM) and for sodium chloride are plotted for comparison. 

Figure 5. Concentration dependence of equivalent conductivity, at 25°C, of SDS, an ordinary micellar solution, and aged aqueous surfactant (S). One mmol/L of surfactant (S) corresponds to 0.0405 wt %. The critical micelle concentration of SDS is 8 mmol/L. For comparison, equivalent conductivities of sodium chloride and sodium iony at infinite dilution, are shown.

An imponant characteristic of electrolyte solutions is that they are electrically conductive. A useful measure is the equivalent conductance, Q, the conductance per mole of charge. A strong electrolyte is one that is completely dissociated into ions. In this case the equivalent conductance is high, and decreases only slowly with increasing concentration. A weak electrolyte is only partially dissociated into its constituent ions, and its equivalent conductance is less than that of a strong electrolyte at any concentration but increases rapidly as the concentration decreases. This is because there is more complete dissociation and therefore more ions per mole of electrolyte in solution as the concentration of a weak electrolyte decreases. Sodium chloride, which completely dissociates into sodium and chloride ions,... 

As sodium acetate is titrated, the acetate ion is replaced by the chloride ion, which, owing to its slightly higher ionic-equivalent conductance, causes a slight increase in conductivity up to the endpoint. Beyond the endpoint, excess hydrochloric acid causes large increases. Such titrations are useful where the ionization constant of the liberated weak acid or base, when divided by the salt s concentration, does not exceed 5 x 10" . If a difunctional acid is formed, then the two ionization constants should differ by about 1Q- if two endpoints are to be observed NajS is an example of this type. Figure 5.9 shows typical replacement titration curves. 

Lithium, sodium, potassium, or other salts of benzoic acid, phthalic acid, sulfoben-zoic acid, citric acid, and others are useful eluents for anions. These are rather large organic anions that are less mobile than most inorganic anions and therefore have lower equivalent conductances. For example. Table 4.1 shows that the benzoate anion has a limiting equivalent conductance of 32 S cm equiv , while chloride, nitrate, sulfate, and other typical sample anions have higher equivalent conductances (approximately 70 S cm equiv. If a sodium benzoate eluent is used, the equivalent conductance is the sum of sodium ion (50) and benzoate (32), or 85 Scm equiv . The equivalent conductance of an anion is the sum of equivalent conductances of the sodium ion (50) and the anion (70), or 120 S cm equiv . On an equivalent basis, this amounts to almost a 50% increase in conductance. 

It has been demonstrated that p increases and then decreases with increasing sodium chloride concentration for sodium nonanoate solutions although the reverse is true of the viscosity. The limiting equivalent conductance A2 permits estimation of the kinetic charge of micelles. "... 

The sensitivity of the UV absorption function was 1.7 x 10 g/ml of toluene with a linear dynamic range of about 1.5 x 10. These specifications compare well with those of the standard fixed wavelength UV detector. The fluorescence function provided a sensitivity of 2.5 x 10 g/ml for dansyl iso-leucine and a linear dynamic range of 1.2 x 10. Finally, the sensitivity of the conductivity function to sodium chloride was shown to be 5 x 10 g/ml with a linear dynamic range of 3 x 10. The response indices were 0.975, 0.95, 1.042 for the UV function, the fluorescence function and the conductivity function respectively. The dispersion of the cell was small, equivalent to a standard deviation of about 2.8 iiU... 

Proxiniity to Sea. Seawater is considered to be equivalent to a 3.5% solution of sodium chloride. The salinity of most oceans is 35 grams per thousand and the conductivity of seawater at 15°C is 0.042 ohm/cm. There is abundance of chloride in the marine environment and in industrial zones located in marine environment. A cumulative corrosive effect is caused by both chloride and sulfur dioxide. Chlorides can absorb moisture at low relative humidities. Saturated NaCl solution is in equilibrium with a relative humidity of 78%, but saturated ZnCla solution is in equilibrium with only 10%. 

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