Polarographic Coefficients of Some Elements in the Method of Amalgam Polarography with Accumulation
Abstract Generated abstract
This study determines standard polarographic coefficients for elements analyzed by amalgam polarography with accumulation in several commonly used supporting electrolytes. Using previously defined coefficients for stirring, electrolysis, sensitivity, peak shape, attenuation, and concentration, the authors report mean experimental values from repeated measurements for elements including copper, lead, cadmium, zinc, and thallium in chloride, fluoride, acetate, ammonia, and tartrate media. The results show substantial variation by element and supporting electrolyte, reflecting differences in analytical sensitivity, diffusion behavior in mercury, and the reversibility of electrode processes. Comparisons such as those for zinc indicate that these coefficients can be used to evaluate favorable media for determination and to characterize anodic and cathodic wave behavior.
Full Text
POLAROGRAPHIC COEFFICIENTS OF SOME ELEMENTS IN THE METHOD OF AMALGAM POLAROGRAPHY WITH ACCUMULATION
Communication II
M. S. ZAKHAROV, A. V. KONKOVA
(Presented by the scientific-methodological seminar of the CTF)
As is known, for one and the same element on different supporting electrolytes and under different hydrodynamic conditions during the accumulation of the substance in the mercury electrode, and at different pH values of the solution, anodic waves may be obtained that differ in shape, depth, etc. In connection with this, to characterize anodic waves, cathodic peaks, and the electrolysis current, in works [1, 2] a number of coefficients were proposed: \(\gamma_{\mathrm{p}}^{0}\), \(\gamma_{\mathrm{e}}^{0}\), \(\gamma_{\mathrm{ch}}^{0}\), \(\gamma_{\mathrm{f}}^{0}\), \(\gamma_{0}^{0}\), \(\gamma_{\mathrm{k}}^{0}\)—the coefficients of stirring, electrolysis, sensitivity, shape, attenuation, and concentration under standard conditions \((t = 25^\circ\mathrm{C}, w = 10^{-2}\ \mathrm{V/sec};\ K_1 = 500z\ \mathrm{a\cdot cm\cdot mole}^{-1})\):
\[ \gamma_{\mathrm{f}}^{0}=\frac{K_2^{0}}{K_3^{0}}=\frac{K_2}{K_3}; \tag{1} \]
\[ \gamma_{\mathrm{p}}^{0}=\frac{500zD_1^{0.45}}{K_3^{0}}; \tag{2} \]
\[ \gamma_{\mathrm{k}}^{0}=100,\quad (3);\qquad \gamma_{0}^{0}=\frac{\gamma_{\mathrm{f}}^{0}}{\gamma_{\mathrm{p}}^{0}},\quad (4);\qquad \gamma_{\mathrm{e}}^{0}=100\gamma_{0}^{0},\quad (5);\qquad \gamma_{\mathrm{ch}}^{0}=100\gamma_{\mathrm{f}}^{0},\quad (6). \]
\[ K_3^{0}=K_3\frac{0.1}{w^{1/2}},\quad (7);\qquad K_3=\frac{I_3}{SC},\quad (8);\qquad K_2=\frac{zFr}{3}\frac{I_2}{q},\quad (9). \]
\(K_1, K_2, K_2^{0}, K_3, K_3^{0}\)—constants of electrolysis of the anodic wave and cathodic peak (the superscript \((^{0})\) denotes standard conditions);
\(w\)—rate of change of potential, V/sec;
\(I_2, I_3\)—anodic and cathodic currents, A;
\(S\)—area of the mercury dropping electrode, cm\(^2\);
\(C_1\)—concentration of ions in solution, mole/ml;
\(F\)—Faraday number (96500);
\(r\)—radius of the mercury dropping electrode, cm;
\(z\)—number of electrons;
\(q\)—area under the anodic wave, coulombs.
Up to the present time, the literature contains no information on the determination of the polarographic coefficients of elements. The availability of these data would make it possible to draw conclusions about the comparative sensitivity, reversibility of electrode processes, etc., on different supporting electrolytes.
The present work is devoted to determining the polarographic coefficients of elements most reliably determined by the method
Table
Polarographic coefficients obtained for various elements
in several supporting electrolytes
| Supporting electrolyte | Element | $K_2^0$ | $K_3^0$ | $\gamma_{\mathrm{n}}^0$ | $\gamma_{\phi}^0$ | $\gamma_0^0$ | $\gamma_{\mathrm{e}}^0$ | $\gamma_{\mathrm{ch}}^0$ | $D_1 \cdot 10^5$, cm$^2$ sec$^{-1}$ |
|---|---|---|---|---|---|---|---|---|---|
| 0.25 M HCl | Cu | 290 | 46 | 0.067 | 6.8 | 102 | 10200 | 680 | 0.26 |
| 0.25 M HCl | Pb | 255 | 50 | 0.169 | 5.1 | 31.0 | 3100 | 510 | 0.824 |
| 0.25 M HCl | Tl | 92.5 | 16.5 | 0.205 | 5.7 | 27.8 | 27800 | 570 | 1.5 |
| 0.1 M NaF | Cu | 250 | 80 | 0.05 | 3.2 | 64.0 | 6400 | 320 | 0.404 |
| 0.1 M NaF | Pb | 192.5 | 60 | 0.087 | 3.2 | 36.0 | 3600 | 320 | 0.855 |
| 0.1 M NaF | Cd | 130 | 61.5 | 0.072 | 3.1 | 43.0 | 4300 | 310 | 0.597 |
| 0.1 M NaF | Tl | 70.5 | 22 | 0.172 | 3.2 | 18.6 | 1860 | 320 | 1.88 |
| 0.1 M NaF | Zn | 207 | 60.5 | 0.083 | 3.3 | 39.8 | 3980 | 330 | 0.76 |
| 0.1 M KCl | Cu | 127 | 50 | 0.05 | 2.25 | 45.0 | 4500 | 225 | 0.184 |
| 0.1 M KCl | Pb | 220 | 60 | 0.089 | 3.2 | 36.0 | 3600 | 320 | 0.824 |
| 0.1 M KCl | Tl | 120 | 24 | 0.148 | 5 | 33.8 | 3380 | 500 | 1.74 |
| 0.1 M KCl | Cd | 215 | 87.7 | 0.055 | 3.5 | 63.5 | 6350 | 350 | 0.67 |
| 0.1 M NH$_4$OH + 0.1 M NH$_4$Cl | Cu | 123 | 50 | 0.105 | 2.5 | 23.7 | 2370 | 250 | 0.85 |
| 0.1 M NH$_4$OH + 0.1 M NH$_4$Cl | Pb | 250 | 60 | 0.08 | 4.1 | 51.0 | 5100 | 410 | 0.675 |
| 0.1 M NH$_4$OH + 0.1 M NH$_4$Cl | Cd | 215 | 57.7 | 0.0675 | 3.5 | 52.0 | 5200 | 350 | 0.427 |
| 0.1 M NH$_4$OH + 0.1 M NH$_4$Cl | Zn | 117 | 54 | 0.16 | 2.1 | 13.1 | 1310 | 210 | 2.6 |
| 0.1 M NH$_4$OH + 0.1 M NH$_4$Cl | Tl | 75 | 26 | 0.077 | 3 | 3.9 | 3900 | 300 | 0.46 |
| 0.1 M CH$_3$COONa | Cu | 180 | 88 | 0.0477 | 2 | 42.3 | 4230 | 205 | 0.515 |
| 0.1 M CH$_3$COONa | Pb | 167 | 70 | 0.078 | 2.4 | 30.5 | 3050 | 240 | 0.925 |
| 0.1 M CH$_3$COONa | Cd | 160 | 44 | 0.104 | 3.5 | 33.6 | 3360 | 350 | 0.64 |
| 0.1 M CH$_3$COONa | Zn | 120 | 75 | 0.06 | 1.6 | 26.6 | 2660 | 160 | 0.601 |
| 0.1 M CH$_3$COONa + 0.1 M CH$_3$COOH | Cu | 180 | 80 | 0.056 | 2.2 | 39.2 | 3920 | 225 | 0.57 |
| 0.1 M CH$_3$COONa + 0.1 M CH$_3$COOH | Pb | 197 | 60 | 0.0895 | 3.28 | 36.6 | 3660 | 328 | 0.91 |
| 0.1 M CH$_3$COONa + 0.1 M CH$_3$COOH | Cd | 190 | 48 | 0.093 | 6 | 64.5 | 6450 | 600 | 0.622 |
| 0.1 M NH$_4$OH + 0.1 M (NH$_4$)$_2$C$_2$H$_4$O$_6$ | Cu | 82 | 56.7 | 0.089 | 1.45 | 16.3 | 1630 | 145 | 0.78 |
| 0.1 M NH$_4$OH + 0.1 M (NH$_4$)$_2$C$_2$H$_4$O$_6$ | Pb | 101.6 | 56.7 | 0.064 | 1.79 | 28.0 | 2800 | 179 | 0.4 |
| 0.1 M NH$_4$OH + 0.1 M (NH$_4$)$_2$C$_2$H$_4$O$_6$ | Cd | 134 | 121 | 0.089 | 1.11 | 28.5 | 2850 | 111 | 0.7 |
| 0.1 M NH$_4$OH + 0.1 M (NH$_4$)$_2$C$_2$H$_4$O$_6$ | Zn | 118 | 158 | 0.035 | 0.747 | 21.3 | 2130 | 74.7 | 0.97 |
| 0.1 M NH$_4$OH + 0.1 M (NH$_4$)$_2$C$_2$H$_4$O$_6$ | Tl | 38 | 91.3 | 0.089 | 0.416 | 10.7 | 1070 | 4.16 | 1.8 |
Continuation of the table
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|
| 0.1 M NH₄OH + 0.3 M (NH₄)₂C₄H₄O₆ | Cu | 82 | 58,2 | 0,077 | 1,41 | 18,3 | 1830 | 141 | 0,62 |
| 0.1 M NH₄OH + 0.3 M (NH₄)₂C₄H₄O₆ | Pb | 103 | 47 | 0,079 | 2,19 | 27,6 | 2760 | 219 | 0,4 |
| 0.1 M NH₄OH + 0.3 M (NH₄)₂C₄H₄O₆ | Cd | 164,5 | 120 | 0,040 | 1,37 | 34,2 | 3420 | 137 | 0,7 |
| 0.1 M NH₄OH + 0.3 M (NH₄)₂C₄H₄O₆ | Zn | 121,2 | 158 | 0,0356 | 0,766 | 21,5 | 2150 | 76,6 | 0,97 |
| 0.1 M NH₄OH + 0.3 M (NH₄)₂C₄H₄O₆ | Tl | 41 | 80,3 | 0,045 | 0,51 | 11,3 | 1130 | 51 | 1,8 |
| 0.1 M NH₄OH + 0.6 M (NH₄)₂C₄H₄O₆ | Cu | 70 | 59,7 | 0,077 | 1,17 | 15,2 | 1520 | 117 | 0,54 |
| 0.1 M NH₄OH + 0.6 M (NH₄)₂C₄H₄O₆ | Pb | 108,5 | 48 | 0,077 | 2,26 | 29,4 | 2940 | 226 | 0,4 |
| 0.1 M NH₄OH + 0.6 M (NH₄)₂C₄H₄O₆ | Cd | 122 | 108 | 0,0445 | 1,13 | 25,4 | 2540 | 113 | 0,7 |
| 0.1 M NH₄OH + 0.6 M (NH₄)₂C₄H₄O₆ | Zn | 230 | 157 | 0,035 | 1,46 | 41,6 | 4160 | 146,4 | 0,97 |
| 0.1 M NH₄OH + 0.6 M (NH₄)₂C₄H₄O₆ | Tl | 38,8 | 82 | 0,0441 | 0,47 | 10,6 | 1060 | 47 | 1,8 |
| 0.3 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Cu | 79 | 67,6 | 0,063 | 1,17 | 18,6 | 1860 | 117 | 0,54 |
| 0.3 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Pb | 98,4 | 57,5 | 0,065 | 1,71 | 26,3 | 2630 | 171 | 0,4 |
| 0.3 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Cd | 141 | 131 | 0,0365 | 1,08 | 29,5 | 2950 | 108 | 0,7 |
| 0.3 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Zn | 117 | 165 | 0,034 | 0,71 | 21,0 | 2100 | 71 | 0,97 |
| 0.3 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Tl | 36,8 | 86,5 | 0,042 | 0,426 | 10,2 | 1020 | 42,6 | 1,8 |
| 0.6 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Cu | 77,5 | 67,6 | 0,068 | 1,14 | 16,8 | 1680 | 114 | 0,54 |
| 0.6 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Pb | 112 | 58 | 0,064 | 1,93 | 30,0 | 3000 | 193 | 0,4 |
| 0.6 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Cd | 131 | 138 | 0,035 | 0,95 | 27,0 | 2700 | 95 | 0,7 |
| 0.6 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Zn | 113 | 172 | 0,0327 | 0,66 | 29,0 | 2900 | 66 | 0,97 |
| 0.6 M NH₄OH + 0.1 M (NH₄)₂C₄H₄O₆ | Tl | 40 | 82 | 0,044 | 0,488 | 11,1 | 1110 | 48,8 | 1,8 |
amalgam polarography with accumulation (Cu, Pb, Sb, Cd, Zn; Tl, Bi, Sn, Ga), in several electrolytes frequently used in polarographic analysis (0.1 M NaF; 0.1 M NH\(_4\)OH + 0.1 N NH\(_4\)Cl; 0.1 M KCl; 0.1 M CH\(_3\)COONa; 0.25 M HCl; 0.1 M CH\(_3\)COONa + 0.1 M CH\(_3\)COOH; \(m\)M NH\(_4\)OH + \(n\)M (NH\(_4\))\(_2\)C\(_4\)H\(_4\)O\(_6\)). It should be noted that, for some of the indicated elements in the electrolytes studied, anodic waves were not obtained.
The table gives the mean values of the experimental data obtained from three measurements. It is evident from the table that the sensitivity coefficients (\(\gamma_{\mathrm{ч}}^{0}\)) of different elements, and of the same element in different supporting media, may differ. Fluctuations in the values of the sensitivity coefficients of one element in different supporting media, at the same concentration coefficient, are due to the degree of reversibility of the electrode process. For example, for Zn, for which among all the divalent elements studied the electrode process in the medium 0.1 M NH\(_4\)Cl + 0.1 M NH\(_4\)OH is the most irreversible, the value of \(\gamma_{\mathrm{ч}}^{0}\) is the smallest. The magnitude \(\gamma_{\mathrm{ч}}^{0}\) also depends on the diffusion coefficients of metal atoms in mercury.
The electrolysis coefficients (\(\gamma_{\mathrm{э}}^{0}\)) and other coefficients of different elements differ considerably from one another, which is also due to the different degree of reversibility of the electrode processes.
From a comparison of the sensitivity coefficients for zinc in several supporting media, it is evident that the sensitivity of zinc determination in 0.1 M NaF is approximately twice as high as that in 0.1 M CH\(_3\)COONa. To achieve the same degree of concentration (\(\gamma_{\mathrm{k}}^{0}=100\)) when carrying out electrolysis in the media 0.1 M NaF and 0.1 M NH\(_4\)OH + 0.1 M NH\(_4\)Cl, in the second medium the intensity of stirring of the solution must be approximately 1.9 times greater than in the first medium. From a comparison of \(\gamma_{0}^{0}\) in the first and second media, it is seen that the ratio between the constants of the anodic current and the electrolysis current in the first medium is more favorable than in the second. A comparison of \(\gamma_{\mathrm{э}}^{0}\) for zinc in different supporting media shows that in 0.1 M NaF the current of anodic dissolution of zinc amalgam exceeds the electrolysis current to a considerably greater extent than in 0.1 M NH\(_4\)OH + 0.1 M NH\(_4\)Cl and 0.1 M CH\(_3\)COONa, which also accounts for the larger value of \(K_{2}^{0}\) in the first medium compared with the other two media.
From the values of \(\gamma_{\phi}^{0}\) for zinc in the indicated supporting media, it is evident that in 0.1 M NaF the anodic peak, in comparison with the cathodic one, is sharper than in the other two media. Analogous comparisons can also be made for other elements. Thus, the experimental data obtained show that, in accordance with theoretical considerations, the above polarographic coefficients may serve as characteristics of the sensitivity of element determination and of the reversibility of electrode processes.
In conclusion, we express our gratitude to Professor A. G. Stromberg for his attention to the work.
Conclusions
For a number of elements in several supporting media, amalgam-polarographic coefficients have been obtained which characterize the sensitivity of element determination and the degree of reversibility of their electrode processes.
References
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M. S. Zakharov, A. G. Stromberg. Journal of Analytical Chemistry, 19, 913, 1964.
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A. G. Stromberg, M. S. Zakharov. Journal of Analytical Chemistry (in press).