T H E FARADAY-EFFECT OF ELECTROLYTES I N AQUEOUS SOLUTIONS. I1 BY E. BUCH ANDERSEN AND R. W. ASMUSSEN
In the previous work' we published measurements of the Faraday-effect for 43 aqueous solutions of simple inorganic compounds. We could demonstrate that the so-called relative molecular rotation of these compounds can approximately be computed by adding together the rotations of the ions in question, which later we determined from the material as a whole, taking the rotation of the hydrogen ion as equal to 0. Our material was comprised of compounds of the cations H, Li, Na, K, Rb, Cs and NH4 with the anions F, C1, Br, I, OH, ClOs, BrOs and 1 0 8 . In the present work we have continued our efforts to bring forth a more systematical inorganic material, having measured the rotation of a further 4 2 aqueous solutions comprising a number of compounds of alkali-ions with especially sulphurous anions. Besides these, some other compounds have been introduced. The material has been so chosen that it should give information as to how the magnetic rotation of certain compounds will be altered when an oxygen or sulphur atom is added, or when an oxygen atom is replaced by a sulphur atom. I n this way is produced a new collection of examples showing the extraordinary importance of the constitution with regard to the magnetic rotation. Our apparatus is the same as was used in the last work and the earlier treatise contains a detailed description of the experimental technique. All measurements have again been taken a t o°C and for the wavelength 5 4 6 p p . A small alteration in our method of working has been introduced, as we no longer determine the zero position of the polarisation apparatus with each individual measurement. By turning the current in the solenoid the rotation is measured alternately on both sides of the zero-point, the position of this being thus eliminated. Table I contains the results of our measurements. The first column gives the substance measured. We have, just as in the previous case, used the purest possible substances for preparation of the solutions, which substances have in several cases been subjected to further purification. We prepared some compounds ourselves. The second column (m) gives the molecular weight of the material measured. The third column (%) gives the percentage of the substance contained in the solutions. The figures have been determined by analysis. Further details about some of the methods of analysis are given below. p is the amount of g-mol. of water per g-mol. of dissolved substance in the solution. It may be seen from the table that we, in the present work, have been measuring 1
J. Phys. Chem., 36,2819 (1932).
E . BUCH ANDERSEN A N D R. I%-. ASYUSSEN
2828
TABLE I Magnetical Rotation of the Polarisation Plane. 0°C. X
= 546,~~ v ?VI d DdD, m % ir I .09 34.016 30.42 HzOs 4,319 I . 1229 0.9792 0 . 0 1 5 2 [.IO I ,0620 0.9930 0.0154 I O .16 HzOz 15.67 I O .j2 16.06 1,0413 0.9947 0.0154 I .08 HzOz I . 0000 1.0043 0.0156 5.37 34.086 0.2303 819.7 HsS I .2084 1 . 4 5 7 0 0.0226 12.67 25.71 19.23 110.27 KzS 3.681 160.16 I ,0410 I ,0811 o ,0168 1 2 . j 2 XIS ICCN 6.595 I . 1869 1 . 1 5 9 7 0,0180 3.38 65.108 35,39 18.66 1 5 . 7 5 1.0973 1.0945 O . O I j 0 KCK 3.57 I ,0184 1,0159 0.01j8 3,31 2.883 1 2 1 . 7 KCN 1.0259 I ,0069 0.0156 2.37 81.108 3.905 110.8 KOCN 3 . 0 8 1 1.3925 I ,8401 0.0285 8 . 1 2 97.178 63.65 KSCN 8.10 KSCN 15.36 I ,1441 1 2934 0 , 0 2 0 1 25.99 1.0222 KSCN 1.0453 0.0162 8.33 4.140 124.9 8.84 76.118 21.32 NHdSCN 15.59 I ,0541 I .2998 0 , 0 2 0 2 NH 4SCN 3.276 124.8 I ,0076 = ,0437 0.0162 8.84 60.048 5.513 5 7 ' I3 1 . 0 1 7 7 I , 0 1 5 2 0.0158 3.18 CO(NHz)z 0.01.jh I . 0 0 7 j I ,0077 CO(NHs)z 3.35 2.415 134.7 7 6 . 1 1 8 6.071 65.37 I ,0206 1.0979 O.Olj0 9.17 CS(NHs)z 1 . 0 1 0 g I ,0516 0.0163 9.79 CS (SHz)z 3.093 132.4 1.6;jq 2 . 1 8 2 7 0.0339 4.66 0 118.99 IO0 SOCIZ 1.7087 I ,3485 0 . 0 2 0 9 0 SOzC12 1.53 134.99 IO0 I ,0287 I ,0030 0.0156 1.93 HzSO4 3.870 1 3 5 . 2 98.09 11.84 I ,2321 1.0737 o.016j 4.87 (Pu"a)nSO1 1 3 2 . 1 5 38.25 I ,035; I .or85 0 . 0 1 5 8 5.146 135.2 (SH4)zSOd 4 99 6,83 30 89 28.34 I . 1897 I ,0204 o.o15a 7.867 148.4 1 ,044.; I , 0 0 2 9 0.01j6 6.26 I ,0998 1.0977 0.0170 i , 2 4 8.565 74-71 I ,0528 I ,0506 0.0163 6.58 3.475 194.4 1 . 2 8 2 5 1.3'06 0,0203 9.42 29.87 20.61 1 ,0525 I ,056; o ,0164 9.33 6.033 136,7 9.96 40.64 15.43 I ,3687 1.3368 0 . 0 2 O . i I ,0586 I ojog 0.0163 9.47 7.341 I33 4 56.59 6,311 1 . 3 1 5 2 1 5863 o 0246 1 1 . 2 2 5.875 131.8 I ,0350 I ,0516 o ,0163 10.47 8.622 121.3 I , 0 6 7 5 1 0239 0.01j9 6.00 8.859 154.4 I ,0607 I , 0 2 8 0 0.0159 9 '79 I , 0263 o .OI59 I .0;6; 8.263 166.6 9 82 13 . 2 4 1.0932 I ,0618 0.016; 13.60 106.j 12.70 115.4 I 08j8 I , 0 5 9 1 0.0164 13.56 16.87 I ,0832 I ,0669 6.737 2 4 8 . 1 0.0173 1 . 5 1 1 4 1.1164 3.48 8.381 47.79 2.68 26.71 1 . 1 2 1 4 1 . 0 2 1 4 0 . 0 1 5 8 17.22
Substance
'
'
'
* Thc potassium penthathionate solution contains further potassium chloride; refer to
text.
FARADAY EFFECT OF ELECTROLYTES
2829
solutions decidedly more diluted than in the previous experiments, since both the empiric agreement between the individual measurements and calculation of the probable error have proved the justification of this extension of the field of measurement. We have not yet, however, been able to work with “diluted solutions” as these are understood in physical chemistry. d is the specific gravity of the solution at oo in relation to water a t 0’. D2/D1indicates the rotation of the solution a t oo relative to that of water a t the same temperature and in the same thickness of layer, reduced to the same current in the solenoid. The rotation of water was measured regularly throughout the whole work; Altogether 88 determinations of this quantity have been made. The rotation of each solution was measured from 4 to 8 times ( z to 4 times by each observer), this being divided as a rule on two working days. The figures in the table represent the average of these measurements. The measured (double) angles of rotation were of the order of magnitude 3Oo-4O0. V is Verdet’s constant in minutes of arc, calculated as described in our earlier paper. Finally, M is the relative molecular rotation of the dissolved substance, when the molecular rotation of water is fixed equal to I. The error in the quoted values of M will be ca. I%. As to the methods of preparation and analysis we shall give some brief particulars. H2S was determined by oxidation with iodine and titration by Volhard’s method. K2S was prepared by ourselves. The sulphide was determined by oxidation with hypobromite and iodometric titration after the method of Willard and Cake.2 KOCN prepared by ourselves, recrystallized from methyl alcohol. Analysis according to Mel10r.~ SOCl2 and SO2C12. Kahlbaum’s preparates. Purified by redistillation. NazSOa. Analysis by Willard and Cake’s method.2 Nu2SzOs. Kahlbaum’s preparate, twice recrystallized. Efforts have been made to determine the dithionate by oxidation to sulphate in alkaline solution with hydrogen peroxide or bromine. Neither of these processes gave any quantitative oxidation. Oxidation with potassium chlorate and nitric acid did not take place quantitatively either. We therefore determined the concentration of the solutions by evaporation and drying over an argand-burner. K~S30s.We tried to produce the salt by Willstatter’s method: but this method only gave a small yield of an impure product. The salt used was produced by Raschig’s method5and recrystallized. By qualitative tests it proved to be free from thiosulphate and other polythionates. Quantitative determinations were undertaken by Kurtenacker and Bittner’s method,’ with methyl-red as indicator. The finished product gave by analysis I O O . potassium trithiorate.
* J. Am. Chem. SOC., 43, 1610(1921). a
Z.anal. Chem., 40, 17 (1901).
Ber., 36, 1831(1903). “Schwefel- und Stickstoffstudien,” p. 296. e Z. anorg. Chem., 142, 119 (1925).
~ ~ ~
2830
E. BUCH ANDERSEN AND R . JV. ASMUSSEN
K2S406.Produced by Raschig’s method’ and recrystallized; proved to be free from sulphite, thiosulphate, trithionate and pentathionate, but contained traces of sulphate. Quantitative determinations by Kurtenacker’s method8 on the finished product gave 99.7770. K2S6Oa.Produced by Raschig’s method.9 Analytical method analogous to that which was applied to the tetrathionate. The resultant substance contains a considerable amount of potassium chloride, and it turned out to be impossible to remove this quantitatively without a further simultaneous extensive decomposition of the pentathionate. Having a number of times vainly tried to bring about a purification we decided (as the production of the pentathionate is rather protracted) to carry out the optical measurements on a solution which contained both salts. A solution of this kind was produced, analysed and its rotation measured. A definite quantity of potassium chloride was then added to a definite quantity of the solution, and the resultant solution was again analysed and the rotation measured. The molecular rotation of potassium pentathionate was established from these two determinations, and the rotation of the potassium chloride was eliminated by use of the rule of addition. The figures quoted in the table show some examples of the importance of the constitution with regard to the magnetic rotation. It is, however, only the most outstanding features which will appear, and one dare not draw conclusions of a more extensive sort from this basis. The cause of this lies only in a lesser degree in the errors of measurement, which, as stated, amount to ca. 1% of the M-values. Of much greater importance is the alteration of the molecular rotation with the concentration which, as may be seen in the table, can in some cases amount to 10% of the value of the rotation. Figures of real value for the purposes of accurate comparison should therefore be provided by measuring each individual substance in a larger number of different concentrations and then extrapolate the results to infinite dilution. As far as material exists, M does not, however, in most cases seem to approach any limit within the concentrations which can be treated experimentally. The following examples of the constitutional influence on the magnetic rotation have been taken from diluted solutions with approximately the same value for p. I. Addition of 0.
Hz02 - Hz0 KOCN - KCN
AM 0 1
-0.9
I. Addition cf 0.
AM
NazS04- NaZSO3 so2c12 - SOClZ
-2 . 7 -3
2
As the rotation of NazSOc has not been measured, this has been established from the rotation of (NH,)SO4, the difference (“,)SO4 - NazS04 being taken as equal to the difference (NHP)zSZO~ - NaZS203. 7
“ S und N-studien,” p. 289. 134, 265 (1924). “ S und N-studien,” p. 276.
* 2. anorg. Chem.,
FARADAY EFFECT OF ELECTROLYTES
11. Addition of 9.
NazSz03 - NatSOa K2S606- K2Sa06 KzS406 - KzS306
AM 2
.a
3.3 3.7
11. Addition of S.
KzS306 - KzS206 KSCN - KCN
283 I AM 3.7 5 .o
The rotation of K2S206 is calculated by means of the difference KzSzOs Na2Sz03. We observe the fact that the discrepancy in properties which are otherwise often found between the dithionic acid and the polythionic acids does not appear here. With regard to magnetic rotation the dithionic acid falls very nicely in line with the polythionic acids. 111. Substitution of 0 with S. AM HzS - HzO 4.4 (NHa)zSz03 - (NHI)zSOI 5 . 5
111. Substitution of 0 with S. AM
KSCN - KOCN 6 .o CS(NHz)z - CO(NHe)a 6 . 4
We thank the director of the laboratory, Prof. Dr. Julius Petersen, for his kind permission to use the means of the laboratory for this work. Chemical Labmatory A . Royal Technical College, Copenhagen. April 87, 19%.
