The half- wave potential, the diffusion coefficient and the diffusion current constant of + 6 uranium in the supporting electrolyte containing 1.60 g/l salicylic acid, 0.4% v v sulphuric acid and 0.009 % thymol (as maximum suppressor) have been determined. The electrocapillary curve of mercury in this electrolyte is also given

M. Branica

O. A. Weber

V. B. Vouk

English

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AR HI V Z A KE M I JU 25 (1953) 23~ Polarographic Behaviour of + 6 Uranium in a Mixture oi Salycilic and Sulphuric Acid 0. A. Weber, M. Branica and V . B. V ouk Institute fo'r Medical Research, Yugoslav Academy of Sciences and A r t s, Zagreb, Croatia Recei ved November 11, 1953 The half-wave potential, the diffusion coefficient and the diffusion current constant of + 6 uranium in the supporting electro-lyte containing 1.60 g/l salicylic acid, 0.4,o/o v/v sulphur ic acid and 0.009°/o thymol (as maximum suppressor) have been determined. The electrocapillary curve of mercury jn this electrolyte is also given. An aqueous solution of salicylic acid (1.60 g/1) and sulphuric acid (0.4°/1) v/v) containing 0.0090/o of thymol as maximum suppressor has proved a very suit able supporting electrolyte for + 6 uranium.1 In the present paper m easur e-ments and calculations are reported of the half-wave potential, th e diffusion coefficient and the diffusion current constant of + 6 uranium in this m edium EXPERIMENTAL Reagents used in this study were the same as described previously.1 In addition tc the Cambridge polarograph, a »Polarograf Heyrowsky« Model V-301 (Ceskoslo-venska :Obrojovka, Erno) was used. The recorder sensitivity of this apparatus was 3.60 X 10-9 A/mm. A »Philoskop II« (Philips GM 4144) ll'Iliversal br idge with external current source (»NF-Schwebungsoszillator «, Philips GM 2307) and an electronic voltmeter Philips GM 6005 were employed for resistance measurements. The potential differ ence on the bridge was calibrated with a standard Weston cell. The rate of mercury flow from the capillary was m easured by the method of Kolthoff and Lingane2 using an experimental arrangement described by Filipovic3 .. Measurements were carried out in the same electrolyte at 0 volts with respect to the saturated calomel electrode. The tempera·ture was kept at 25 ± 0.1 oc by means of a constant temperature water bath. l{ESUL'l'S AND DISCUSSION T he half -wave potent i al The h alf-w ave potential of + 6 uranium in the above m en tioned electro -lyte w as calculated from the dat a given in Table 1 by applying the least-squares m ethod.4 The correction for th e potential drop iR amounted to less th an 2 X 10-4 volts and was neglect ed. The values of the diffusion current and , the r~sistance R (for 3000 c./sec.) at the h alf wave potential were 305.9 X 10-9 A and 1300 ohms, resp ectively. Under these conditions a value of 0.2127 .volts with standard er ror of ± 0.0007 volts was ob tained for the half w ave potential .of + 6 uranium. 236 0 . A. WEBER, M. BRANICA AND V. B. VOUK TABLE 1 Ede ~1 180 I 190 I 200 I 210 I 220 : 2251 230 I 240 I 250 mV I I i I 8.3 , 11.1 I I 18.31 22.0 1 · 23.51 I I 7.5 I 14.5 25.2 28.9 31.3 mm I I I ! ia = 38.5 mm The relationship between the potential (Eae) and log i/(i,z - i) was linear with a slope of 0.0591 ± 0.0006 volts which is in perfect agreement with the theoretical value of 0.0591 volts for a reduction process at 25°C involving 1 F of .:lectricity. Therefore, it is reasonable to assume that under these experimental con-ditions the electrode reaction consi.sts in a reversible cathodic reduction of u ranyl ion according to the equation: althougt the observed half-wave potential is slightly more negative than the standard potential (-0.180 volts) of reduction of +6 uranium to +5 ura-nium as measured in other media5•6• This shift of the half-wave potential to the negative side is probably due to the complexing power of the salicylic acid and different acidity conditions. 'The diffusion coefficient The diffusion coefficient may be calculated either from the originaF D = ( id )2 607 n C m 2/31116 (1) Jr the corrected Ilkovic equations·9: D' -[ m1/3 ( 1+·v1 + 4Aid )]2 2 A 1116 607 n C m . (2) w here i d is the mean diffusion current in µ.A; n the number of equivalents ~ nvolved in the electrode reaction; D and D' the diffusion coefficients in cm2 sec-1 ; C the concentration of the reacting substance in millimoles per liter; m the rate of flow of mercury from the capillary in mg.sec-1 ; t the drop-time in sees; and A a constant having numerical value 39 (Lingane and Loveridge!') or 17 (Strehlow and von Stackelberg8). In order to obtain a good estimate of the diffusion current constant and the diffusion coefficient 84 measurements of the diffusion current were per-formed for different uranium concentrations using two polarographs and two capillaries. Thus four independent· estimates of the diffusion current were vbtained for each concentration, each estimate being an arithmetic mean of -two measurements. The uranium concentrations covered a range ·from 2 to 50 / g/ml. The results of the measurements are given in Table 2. If the diffusion POLAROGRAPHIC BEHA VIOR OF +6 URANIUM 237 .currents are expressed in µA, only two series of results are obtained cor-r esponding to the two capillaries used. TABLE 2 CAPILLARY I I II Polarograph Polarograph Cambridge I Heyrowsky Cambridge I Heyrows ky - -- - I h h h h INo.j C I h h h I h '-1----1----'---'------'---~----'---'------2 93.3 49.3 . 150.0 149.7 101.0 101.7 135.6 136.5 92.8 149.4 102.3 137.4 93.9 3 4 5 6 7 8 9 . 10 11 ' 12 113 14 15 16 17 . 18 19 20 21 22 ! i i I I 39.4 29.6 19.7 I 13.8 I ! 13.8 I 9.86 I I 7.89 I I 5.92 : I 3.94 1.97 117.0 116.7 116.4 90.0 89.3 88.5 58.8 5941 60.0 41.4 41.l 40.8 41.2 40.6 40.0 27.8 I 27.8 27.8 I 16.8 17.3 17.8 12.0 11.6 11.8 4.5 4.4 4.3 84.4 83.7 108.6 108.9 83.0 109.2 61.5 61.3 82.8 82.8 61.l 82.8 42.9 42.8 53.4 53.4 42.6 53.4 30.2 30.1 37.2 37.2 30.0 37.2 31.2 30.8 36.6 36.3 30.4 3€.0 22.2 21.8 24.9 I 24.8 21.4 24.7 19.2 19.1 I 19.0 14.2 13.9 14.8 14.6 13.6 14.4 8.4 8.3 8.8 8.2 I 8.0 8.9 5.0 4.0 I 4.6 3.9 4.2 I 3.8 C = uranium concentration in µ;g/ml; h = wave height in mm. 72.8 73.5 73.7 56.4 . 58.2 57.3 38.2 38.4 38.3 27.3 26.9 27.1 27.4 26.6 27.0 19.6 19.0 19.3 16.0 15.8 15.9 12.0 11.8 11.9 8.2 8.0 8.1 3.8 I 4.2 4.0 The r esults of the linear regression analysis performed for these data are giv en in Table 3. The estimation of the diffusion current was done using the regression equations ia = 7.83 C (for the capillary I) and ia = 7.13 C (for the capillary II). Thus a fairly reliable estimate of the diffusion current for a '!'ABLE 3 I Variance about I S lope Standard error of Capillary I the regression I b the slope v Sb I I 18.92 I 7.830 I 0.040 I II I 22.00 I 7.125 I 0.043 238 0. A. WEBER, M. BRA.NICA AND V. B. VOUK choS;en uranium concentration was obtained. Other experimental data neces-·-sary for calculating the diffusion coefficient from the equation (1) and (2) ar~ collected in Table 4. Table 5 contains the calculated values of the diffus ion · coefficient, if 39 is taken as the value of the constant A 9. TABLE 4 I Rate of flow Standard Standard I Mercury column I Drop time/ Capillary I height of mercury enor at 20~ mV I error I m Sm St mm mg sec-1 mg sec-1 I sec sec I I II Uranium concentration c mM/l 540 I 440 Diffusion current id µA 1.421 1.153 TABLE Diffusion coefficient from eq. (1) D X 106 cm2 sec-1 I 0.003 0.010 Standard error of D Sn X 106 cm2 sec-1 I 3.084 4.102 I Diffusion I coefficient from eq. (2) I D' x 106 1 cm2 sec-1 I I I 0.005 0.003 Standard enor of D' sn X 106 cm2 sec-1 I 0.042004 I 0.0783 4.055 0.024 3.488 0.034 I _II___,_ _ o_.04_20_0_4__,_l __ o_.o_n_3 ___ 4_._0_3_4_!. __ o_.0_5_4-'---3-.4_3_4 1 ____ 0.055 -l. Mean values 4.045 3.461 _ The following equations were used for estimating the standard enor of D and D': Sn = n-. -- o - - · 0-1 D V Q + 16 Q + 4 •) '' 9'm 9' (Q is the relative standard error; the subscripts i, m and t refer to the measurements of the diffusion cunent, the rate of flow of mercury and the drop t ime, respecti ''ely),. and: B Q B z . , _ D' \ I ( -1 )- 2 + ! 2 -1 ). 2 1 2 Sn - V B-VB Qi \3- B-VB (/m + 9(ii (4}' 4 Aic1 with B + 1. Both equations were derived by applying the ·well known 607 nCm rule for calculating the standard error of a computed result.11 The diffusion current constant The same data (Table 5) w ere used in calculating the diffusion current. constant 12•13 from the equation: I = 607 nD'h where for D either the value calculated from the original (1) or the corT12cted Ilkovic equation (2) can be substituted. Table 6 gives the calculated values cf I and their standard errors. I Capill ary! I I I I II I ! Mean I values / PO'LAROGRAPHIC BEHAVIOR OF -t- 6 URANIUM TABLE 6 Diffusion current Standard I Diffuo;ion current constant calculated I constant calcula:ted using D error I using D' SI I I I ' I i 1.222 0.004 I 1.134 I 1.219 I 0.008 1.125 1.221 1.130 The standard error was estimated from the equation 607 n sr :;:::: --=So 2V D 239 I Standard I error Sp I 0.006 I 0.009 Electrocapillary curve of mercury in salicylic acid - suphuric acid mixture Since the supporting electrolyte consisting of L6 g/1 salicylic acid, 0.40/o viv sulphuric acid and 0.0090/o thymol is suitable for polarographic determi-nation of various metal ions, the electrocapillary curve of mercury in this medium may be of some interest. For a given capillary the drop time of mercury (t) is proportional to the interfacial tension (a) (t = K . a). Since in polarographic work it is important to know only the form of the electrocapillary curve and not the absolute values of the interfacial tensions, only the drop time (t) of mercury was ... _20 I , I § ---t --t-~ -~ ~ "' 4 ___ · __ __j _______ µ _  ! I I • 4-00 -eoo -uoo POTENTIAL /mV/ v S C E Jo'ig. 1. E lectrocaplllary curv-e of mercu•ry in 1.6 g/l salicylic acid - 0.4'/• v/v sulphuric acid._ Ordiua t.es: drop time (t) in seconds; apscisae: applied potential relative to the saturated calomel · electrode (in mV). measured at different potentials. For each v.alue of the applied potential the drop time for 50 drops was noted, and the drop time of a single drop calculated therefrom. A saturated calomel electrode was used as the reference electrode. The standard error of t did not exceed 0.005 seconds. Figure (1) shows the electrocapillary curve of mercury in this supporting electrolyte. 240 0. A. WEBER, M. BRANICA AND V. B. VOUK REFERENCES · 1. V. B. Vouk, M. Branica and 0. A. W:eber, Arhiv kem. 25 (1953) 225. 2. I .. M. Kolthoff, and J. J. Lingane, Polarography. New York 1946. p . &2. 3. I. Fi 1 i !Pov i c, Arhiv kem. 23 (1952) 133. 4. 0. A. Wl e be r, Arhiv kem. 25 {1953) 231. 5. W; E. Harris and I. M. Ko 1 t ho ff, J . Am. Chem. Soc. 67 (1945) 1484. 6. D. M. H. Kern and E. F . Orlemann, J . Am. Chem. Soc. 71 (1949) 2102. 7. D. I1 k o v i c, Collection Czech. Chem. Communs. 6 (1934) 498. 8. H. S t r eh I o w and M. v o n St a c k e 1 b e r g, Z. Elektrdchem. 54 (1950) 51. 9. J .J . Lingane and B. A. Loveridge, J. Am. Chem. Soc. 72 (1950) 438. 10. See, for iMtance, O. L. D a v i e s, Statistical Methods i n Research and Pro-duction. London 1949. 11. J . J. Ling an e, Ind. Eng. Chem., Anal. Ed. 15 (1943) 588. 12. I . M. Ko 1 t ho ff and J . J. Ling an e, Polarography. New York 1952. p. 70. IZVOD Neke polarografske kar.akteristike +6 urana u sistemu salicilna kiselioa-sumporna kiselina 0. A. Weber, M. Branica i V. B . Vouk U nastavlm rada na odredivanju urana polarografskom metodom1 odr edene su ove polarografske karakteristike urana: po1uvaini potencijal, koeficijent difuzije i konstanta difuzione struje. Kao osnovni elektroli.t sluiila je smjesa salicilne i sum·-porne kiseldne. Odredena je i elektrokapilarna krivulja Zi.ve u tom elektrolitu. INSTITUT ZA MEDIOINSKA ISTRA2IVANJA .JUGOSLA VENSKE AKADEMIJE ZN ANOSTI I UMJETNOSTI . ZAGREB Primljeno 11. novembra 1953 • 

Polarographic Behaviour of +6 Uranium in a Mixture of Salycilic and Sulphuric Acid

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