Sodium equivalent conductivity

Molten sodium sulphate has a specific conductivity 64 3680 XlO-8 (mercury unity). The equivalent conductivities, A, of soln. of lithium, sodium, and potassium sulphates 65 with A7-gram-eq. per litre, are, at 18° ... 

The general shape of the equivalent conductance vs. concentration plot for metal-ammonia solutions is shown by the behavior of sodium in NHs at —33° C. in Figure 2. The conductance behavior of metal-ammonia solutions is quite analogous to the behavior of electrolytes in solvents of low dielectric constant. The dilute region equivalent conductance decreases with increasing concentration, eventually goes... 

Figure 2. Equivalent conductance as a function of concentration for sodium in NHz at —34° from the data of Kraus (26, 30).

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). 

Table 2.6 The limiting equivalent conductivities, A.00, and the Walden products, X°°r, of tetrabutylammonium and sodium ions in various solvents at 25°C (Kratochvil and Yeager 1972, Marcus 1997)... 

Fig. 4. The concentration dependence of various electronic properties of metal-ammonia solutions, (a) The ratio of electrical conductivity to the concentration of metal-equivalent conductance, as a function of metal concentration (240 K). [Data from Kraus (111).] (b) The molar spin (O) and static ( ) susceptibilities of sodium-ammonia solutions at 240 K. Data of Hutchison and Pastor (spin, Ref. 98) and Huster (static, Ref. 97), as given in Cohen and Thompson (37). The spin susceptibility is calculated at 240 K for an assembly of noninteracting electrons, including degeneracy when required (37).

The net effect is that prior to the equivalence point hydronium ion is replaced with sodium ion, while after the equivalence point sodium ion plus hydroxide ion are added to this solution. Because the equivalent conductance of hydronium ion is many times greater than sodium ion, there is a net decrease of the total solution conductance prior to the equivalence piont after this point the conductance increases from the addition of sodium and hydroxide ion (the latter also has a large equivalent conductance). 

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 ... 

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. 

The following values were obtained by Martin and Tartar [J. Am, Chem, Soc,t 59, 2672 (1937)] for the equivalent conductance of sodium lactate at various concentrations at 25 ... 

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. 

The equivalent conductance of a 0.025 n solution of sodium hydroxide was found by Kameyama Trans. Electrochem, Soc., 40, 131 (1921)] to be 228.4 ohms" cm. Tlie addition of various amounts of cyanamide to the solution, so that the molecular ratio of cyanamide to sodium hydroxide was x, gave the following equivalent conductances ... 

From Table 4.1, the equivalent conductance of sodium benzoate will be ZNi. i + u/-... 

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. 

Hence, the major general criterion for eluent selection is a different equivalent conductance compared to the sample ions and a high enough affinity for the resin to promote effective elution of the sample ions. So far we have emphasized that the eluent should have a low equivalent conductance. But an eluent such as sodium hydroxide, with a high equivalent conductance, can be used in non-suppressed 1C. This eluent is discussed in Section 6.3.3.5. 

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 eonductance of 32 S cm equiv, while ehloride, nitrate, sulfate, and other typieal 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 S cm equiv". The equivalent conductance of an anion is the sum of equivalent eonductances 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. 

Anions of very weak acids such as arsenite, borate, carbonate, cyanide and silicate exist as anions only in basic solution. It is therefore necessary to use a basic eluent to separate these anions. A solution of sodium hydroxide can be used. Detection with sodium hydroxide is different than with the organic salt and acid eluents. Since the hydroxide ion is more mobile and has a higher equivalent conductance than most other anions, the peaks for the sample anions appear as negative peaks (decreased conductance). However, the peak height (or area) is still a function of the amount of sample anion and the sensitivity is even better than with the more acidic eluents where positive peaks are obtained. 

This equation can be used for organic acid eluents as well as for sodium or potassium salts or acids. It shows that sensitivity is dependent on the extent of ionization of an acidic eluent as well as the difference in equivalent conductances between the sample and eluent ions. A sample peak is approximately Gaussian and the sample anion concentration Cs changes accordingly as the elution peak develops. 

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