Characterization of Aqueous Dioxane as a Suitable PoI a rogr(3 p hic So Ivent J. L. WALTER, C.S.C., and Sr. M. ROSALIE, O.S.F. Department o f Chemistry, University o f Noire Dame, Notre Dame, Ind.
b Polarographic stlJdies were made in mixtures of dioxane and water in varying proportions; to characterize this system as a suitable solvent medium for the study of inorganic compounds. Polarograms of cadmium(l1) ion in 0 !to 70 weight % dioxane and 0.1 N nitrate, chloride, and perchlorate supporting electrolytes were obtained. Scllvent effects were noted b y changes in the limiting current, half-wave potential, diffusion current constant, density, viscosity, etc. The half-wave potential of cadmium(l1) ion in nitrate medium is similar to those in water, whereas the values in chloride and perchlorate suplporting electrolytes differed as the result of complexing and solvation effects.
T
for the diffusion current. with all the factors which influence it was first derived by Ilkovic (7) and later in more rigorous manner by AIacGillavry and Rideal (12). Experiments in aqueous solution have proved the Ilkovic equation to be essentially correct (11, 16, 20). Kumerous nonaqueous or partially aqueous solvents have been investigated for their suitabilitj- in 1)olarographic studies (1, 2 , 4, 6). Letaw and Gropp (10) have reported virtually ideal polarographic behavior of a number of inorganic ions and organic compounds in formamide bolutions. Khatsyanovskii and Kudra (8) studied the complex chlorides of cadmium in aqueous methanol and aqueous et'hanol Tolution a t low 1ip:and concentration. Only the lower complexes [CdClIf and [CdC12] were observed. Coetzee and Siao (3) found acetone a suitable solvent, especially for the study of the rare earth elements:. The effect of solvent may have a twofold effect upon thi: diffusion current : on the surface tension of mercury, where any altwation will 1)roduce a change in the drop time; and on the diffusion coefficient, D , which is usually smaller in nonaqueous solwnts because of the increascd visrositj-. This investigation will attempt, to determine the effect the solvent has on the various factors of the Ilkovic equation as observed from the polarograms obtained of cadniium(I1) ion in nitrate, HE FCNDAMEXTAL EQUhTION
chloride, and perchlorate supporting electrolytes with varying amounts of dioxane. Such a study is of great practical value because of the use of dioxane-water as a solvent for many inorganic complexes not soluble in aqueous solution. I t also presents a method to determine, by polarography, the diffusion coefficient of metal ions, and to interpret qualitatively the observed variations in diffusion coefficients in dioxane-water mixtures on the basis of solvation and ion pair formation. EXPERIMENTAL
Apparatus and Procedure. A Sargent Model XV polarograph, to which was attached a Sargent iR compensator, was used t o automatically record t h e polarographic curves of current us. effective voltage. T h e mercury reservoir was 31 em. above the level of t h e solution a n d waq attached b y neoprene tubing to a glass capillary 14.0 cm. long with a n internal diameter of 5 mm. T h e capillary constant was 2.16-mg. 2 ' 3 t 1 ' 6 a t 0.9 applied bolt for cadmiuni(I1) ion in 0.1JI KSOs in aqueous solution. Ai yecial polarographic cell (Figure 1) wab set up, which, in addition to the usual microelectrode compartment, had two anodes. One of these, toqether with the microelectrode, made up the electrolysis cell, while the other worked in conjunction with the iR compensator to correct for any voltage drop acrohs the solution. The standard H-shaped cell of Lingane and Laitinen waq uied in which the reaction solution was separated from the electrolyiis reference electrode (R.E. S o . 1) by a ciossarm containing a fritted &,is diik and an agar plug saturated with potas-ium chloride or potassium nitrate, depending upon the wpportinp electrolyte uied. .I capillary tube in the cathodic
Reference Elec Y 2
Figure 1. system
Reference EIec # I
Diagram of three-electrode
chamber containing a fritted glass tip followed by an agar plug led t o the second reference electrode (R.E. No. 2). To prevent distortion of the polarographic wave caused by the effect of overlapping of the electrolysis current path by the microelectrode, the reference electrodes were ranged opposite each other with the dropping mercury electrode directly b e h e e n the two. Sargent's new iR compensator automatically introduces into the circuit enough voltage to compensate for the iR drop and variations in reference electrode potential which may have resulted because of the high electrical resistance of the solutions due t o the presence of dioxane. htniospheric oxygen was eliminated by bubbling pure nitrogen through the solution for 10 to 15 minutes. The nitrogen was presaturated with the same concentration of dioxane-water qolution as in the electrolysis cell to prevent changes in composition of the dioxane-nater ratio in the cell. Xitrogen was also allowed to pas.; over the surface of the solution during electrolysis to prevent re-entry of air. The temperature was maintained a t 26.00" =t 0.01" C. by a Sargent thermostatic water bath. The vkcosity of each solution wa> nieysured with a n Ostwald viscosimeter and denqity measurements were made with a pycnometer of approximately 2-nil. capacity. -A11 measurements were made a t 23.00 i 0.01" c. Each solution studied was 1 m X with respect to cadmium(I1) ion, 0.1X Jiith r e q e c t to supporting electrolyte, and varying amount.; of dioxane given in weight %-Le., the lveight of pure dioyane in 100 ml. of qolution. The polarographic wares were analyzed by Iilotting log i'(irl - i) vs. Edc. .ill currents were corrected by a graphical method for the residual current, and ma\imum currents were used for obtaining value\ of id. Reagents. Stock solutionq of cadmium nitrate, cadmium chloride, and cadmium perchlorate (0.01-11) were prepared by diaqolving t h e corresponding reagent grade per(G. Frederick Smith chlorate Chemical Co.), nitrate, or chloride (J. T. Baker Chemiral Co.) in deionized water. 'The metal ion iolution\ were standardized by direct titration with 0.0211 S a 2 E I > T . l 1 0 1 ~ tion u 4 n q l)\-rocaterhol violet as indicator and diluted t o O . O O l J 1 as needed. VOL. 37, NO. 1, JANUARY 1965
45
Polarographic Studies of Cd(ll) Ion in 0.1M KCI
Table I.
Wt.
71;
dioxane
With iR compensator amp. -El/?, volt 8.42 0.600 8 25 0.601 7.88 0.601 7.21 0.608 6.i2 0.614 6.35 0.638 6.29 0,670 6.22 0 . 700
0.00
10.32 20.53 30.62 40.59
50.4
