The Electrical Conductivities of Some Solutions in Aniline - The

T H E ELECTRICAL CONDUCTIVITIES O F SOME SOLUTIONS I N ANILINE

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 24, 2015 | http://pubs.acs.org Publication Date: January 1, 1927 | doi: 10.1021/j150274a009

BY JAMES RORERT POUND

Frequently the electrical conductivities of non-aqueous solutions are of a different order of magnitude to those of aqueous solutions. Also often the former vary with the concentrations of the solutions in a different manner to the well-known behaviour of aqueous solutions; in the latter solutions the equivalent conductivity, A, rises as the concentration decreases and reaches a more or less definite maximum, A,, but in many non-aqueous eolutions the equivalent conductivity falls as the concentration decreases and approaches the value zero at zero concentration.’ The present paper deals chiefly with the electrical conductivities of some solutions in aniline a t 30’. Qualitative Ezperzments. Two platinum wires were connected through an electric lamp to the city 2 2 0 volt D.C. supply. The wires were placed about half a centimetre apart in various solutions in aniline; and when the current was turned on, the effects were noted. With a few of the best conducting solutions the lamp lit up. In the conducting solutions there was evolution of gas (hydrogen?) at the cathode with more or less rapidity, and a t the anode a dark brown solution appeared and slowly mixed with the bulk of the liquid, which was usually of a light brown colour. These two effects were taken as indications of the conducting power of the solution. If a so!-. tion was a poor conductor and gave no gaseous products on electrolysis, then these experiments would fail to indicate its conducting power. The solutions were of indefinite strength; but if the solute was not very soluble they were saturated. The experiments were done cold and then hot-up to the boiling point of aniline. The aniline was distilled pure aniline (v later), and the solutes were the best commercial products, taken as dry, which certainly was the case with most of them. The presence of water usually increased the conducting power. The solubilities of the solutes varied greatly. More than one hundred substances were tested in this manner. Conducting solutions with aniline were given by the acids and their anhydrides and by the salts of organic bases (if these substances were a t all soluble). Such were acetic acid, acetic anhydride, phthalic acid, phthalic anhydride, salicylic acid, phenylacetic acid, succinic, picric, hippuric, sulphosalicylic, sulphoanilic and other sulphonic acids, monochloracetic acid, rosolic and pararosolic acids; aniline hydrochloride, m-phenylenediamine hydrochloride, ‘methyl violet’ or pentamethylpararosaniline hydrochloride, and similar salts, and saccharin. The conductivities of the first six substances and of aniline hydrochloride and saccharin were investigated quantitatively (v. later), as also were the conductivities of benzoic acid in aniline. Benzoic C. A. Kraus: “The Properties of Electrically Conducting Systems” (1922);Pound: J. Chem. Soc., 99 (1911);121 (1922);125 (1924).


548

JAMES ROBERT POUND

acid, though freely soluble in aniline, gives very poorly conducting solutions, which in these qualitative experiments were classed as non-conducting; thus some of the following non-conducting solutions may be similar to those of benzoic acid. The stronger an acid, the better conducting is its solution in aniline, unless it forms anilides which give poorly conducting solutions (v. later). The salts (hydrochlorides) of complex bases, like methyl violet, seem to give poorer conducting solutions than the salts of simpler bases; but this may be largely due to their differing solubilities. The substances that gave non-conducting solutions with aniline were ( I ) most salts, e.g. potassium cyanate, sodium oxalate, quinine sulphate, aniline sulphate, calomel and zinc valerianate. Most of these salts were very sparingly soluble. (Mercuric chloride is not very soluble in cold aniline; but, on warming, the mixture suddenly turns dark and gives a purple solution or suspension, which with the application of the electric current heats and boils and certainly conducts to an appreciable extent.) It may be noted that many of the suspensions in aniline show appreciable cataphoresis. ( 2 ) Alcohols, phenols and their salts, aldehydes, ketones, esters and ethers, e.g. phenylethyl-alcohol, @naphthol, phenol and potassium carbolate, acetone, acetophenone, salol, methyl-benzoate, anethole and ethyl ether. Some of these substances are said to unite with aniline'; but the compound- or complexformation evidently does not give any appreciable conductivity. (3) Free bases, hydrocarbons, organic chlorides, etc., e.g. urea, m- phenylenediamine, quinine, benzene, iodoform and chlorobenzene. These %on-conducting" solutions are certainly of varying electrical conductivities. Thus the weak acids, like benzoic, camphoric, cinnamic, anthranilic and anisic acids, were included here, though they differ only in degree from the stronger acids that give appreciably conducting solutions. Again, acetanilide is fairly soluble in aniline; its solution was classed as nonconducting; a quantitative measure of its conductivity is given later. Quantitatzve Experiments. All the materials were purified and dried and were kept in desiccators throughout. The aniline was kept for long periods over solid caustic potash, and then distilled; only the middle fractions of constant poiling point were used, and these were of pale yellow colour. The electrical conductivities a t 30' of the samples of aniline varied from 0.000, 000,029 to o.ooo,ooo,o~oohm-cm. units; the former samples are most likely to contain traces of water, the latter to contain higher homologues of aniline. Their densities at 30' varied from 1~01292to 1.01336. One sample of aniline initially had k = .0;206' and D3:0 = 1.01336; this was 48 days after distillation; when finishing work with this sample 60 days later, i.e. 108 days after distillation, it was found that k = ,07273 and D3$ = 1.01332. Thus in two months the density had scarcely changed and the conductivity had increased by .oa7, not an appreciable amount and possibly a n extreme value as the other samples of aniline were used up more quickly than this one. This increase of conductivity was probably due to absorption of traces of Oddo and Tognacchini: J. Chem. Soc., 124 I,

224

(1923).


ELECTRICAL CONDUCTIVITIES O F A N I L I S E SOLUTIONS

549

water. The electrical conductivities of the solutions, as given in the tables, are all "corrected" for the conductivity of the aniline (solvent); that is, the figures in the tables are the conductivities of the solutions as found minus that of the solvent, which latter is shown in the table underneath the figures corrected thereby. The conductivity measurements were made by the usual Kohlrausch (Wheatstone bridge) method. Wireless head-phones, each of a resistance of 2 0 0 0 ohms, were found to be better than lom-resistance telephones. The resistances of the cells containing the solution? were from 50 to 300,000 ohms, excepting with some extreme cases and with t,he aniline alone. Two electrolytic cells were used; their "cell-constants'' were , 1 0 7 2 and .03415. The latter values were found by standardisation at 30' with X/IOO(18") potamium chloride solution, carefully made from the purified salt and water, and assumed to have a t 30' k = 0.001,jjz plus the k of the watsr, which was 0.000,003. In standardising these cells with this dilute potassium chloride solution care was necessary to avoid bubbles forming on the electrodes; by exhausting the air from the stock bottle of the solution for some time before using, this trouble could be minimised. The average error in the determinabion of the resistance of a cell full of electrolyte was * 0 . 3 2 c ; C . The error was somewhat greater when the cell resistance was over 150,ooo ohms. It is well known, however, that in this work larger errors may occur between different or duplicate experiments. In the tables there are given with each soIut4 the independent figures of at least two series of experiments. The cells were placed in a thermostat kept within one or two hundredths of a degree of 30°, using a standardised thermometer. While a solution was in the conductivity cell, there was often a slight tendency for the conductivity to increase, say, by I to j parts in 1000; this may be due t o better contact at the electrodes after slight passage of current. IVhen the solutions in aniline had a lower conductivity than O.OOO,OOI! the error of experiment increases, the influence of traces of moisture and of other disturbing impurities becomes greater, and the conductivity of the aniline itself (or the 'blank' which is subtracted from the observed conductivity to give the value quoted) becomes relatively large; for such solutions therefore the total errors are liable to be large. The mixtures were all made up by weight in well-stoppered weighing bottles, which were kept in desiccators over calcium chloride or sulphuric acid as much as possible. One mixture was made up from solute and solvent; part was used for the determination of the electrical conductivity or density, and the remainder was diluted with further solvent to give a new solution. The parent solutions of a series are denoted in the tables by an asterisk (") after the percentage of solute. The densities ( j o " , ?") of certain solutions were determined with all precautions, and thus the concentrations in gram-molecules per litre at 30' of all the solutions could be determined, since the densitypercentage weight curves for these dilute solutions were practically straight lines.

550

JAMES ROBERT POUND


( I ) Solutions of Acetic Acid in Aniline.

A study of the density, viscosity and electrical conductivity of mixtures of acetic acid and aniline was completed in this laboratory' in 1923; but the whole field of possible mixtures of these substances, with and without water, was then covered. The present work was done with more dilute solutions of the anhydrous liquids. The acetic acid, which had been previously purified, was traced with phosphorus pentoxide, filtered off and distilled, and the middle fraction, B.P. = I19.0-I19.5°, was collected. The electrical conductivities of :hese solutions showed no signs of altering on keeping. The acetic acid concentratione in gram-molecules per litre at 30' were calculated from the percentage weights of acid and from the densities obtained from the 1924 data, from which source we had the following results:Densities and Viscosities of Solutions of Acetic Acid in Aniline a t 30' in C.G.S. Units:% wt. of acid Density Viscosity 16.375 8.1905 2.8880 I . 6234 0

I . 0284

I .0202 1.0154 1.0144 I ,0131

,0450 .0366 ,0336 ,0328 ,03226

With monochloracetic acid dissolved in aniline the conductivity of the solution rapidly increased with time; e.g. with a solution of 0.9% monochloracetic acid in aniline the initial specific conductivity at 30' was about 0.000,002, and this more than doubled after 24 hours' keeping a t IO'. Thus the solution of such a strong acid in aniline is not in equilibrium. With the above solution, crystals (the anilide?) appeared throughout the mixture after half an hour, but these disappeared aft,er two days and then the solution became red-brown, the colour deepening with time and hydrochloride accumulating in the solution. (2) Solutions of Aniline in Acetic Acid. The same materials were used as in ( I ) . These mixtures, when first made, had a slight pink colour; this rapidly faded to a straw colour and on further dilution with the acid became colourless. Here with the mixtures containing small percentages of aniline, i.e. with zYc aniline or less, the electrical conductivity decreased with time, the rate of decrease being greater at 30' than a t room temperature (IO' to 20°), and consequently these results, marked 8, are but approximate. In any experiment where the electrical conductivity was found to vary, the initial values are given in the tables. With mixture 39 the conductivity decreased to half the original value after 24 hours a t room temperature, zoo, though with mixture 38 no decrease in conductivity was noticed. With mixture 44 the conductivity decreased by 0.35% while the determination was being made, i.e. within 1,!4 hour at 30°, and by 2 2 7 0 after 4 hours a t 25'. This decrease in Conductivity with time is probably connected with the action of the aniline and the acetic acid to form acetanilide and Pound and Russell: J. Chem. SOC., 125, 769;Pound: 1560 (1924).


ELECTRICAL CONDUCTIVITIES O F ANILINE SOLUTIOKS

551

water; this action is faster probably in acetic acid solution than in aniline solution; the acetanilide forms poor conducting solutions in both these solvents (pp. 551, 552). However water is formed a t the same time by this condensation, and this would tend to make the solutions better conductors. Thus the change in the Conductivity of aniline dissolved in acetic acid will not be simple; and it might happen that the same action, which would produce a decrease in conductivity in dilute solutions. might produce an increase in conductivity in more concentrated solutions. The 1923 results with aniline in acetic acid are higher than these results but parallel to them. The present results are the better, the liquids being purer and drier. It might be noted that the conductivity of the acetic acid more than doubled during the course of the experiments over the period of one month; but the last of these experiments, 42 to 44, were done three weeks after the previous three series. This increase in conductivity is certainly due to the absorption of traces of water. The densities and viscosities of these solutions were taken from the I923 data, e.g. :-

70wt. Aniline 28 693 21.010

Density (30"/4") I . 08426 I ,08125

Viscosity (30') 0.1371

0 .0103 I

(3) Solutions of Acetic Anhydride in Anzline.

The acetic anhydride was prepared from May and Baker's "Acetic Anhydride". Sample ( I ) used in experiments 46 to j I was obtained by shaking the original with phosphorus pentoxide for some minutes, filtering and distilling. The collected distillate was the last third and had B.P. = 137 o139.4'; its conductivity a t 30' was 0.000,001,7j.Sample ( 2 ) of acetic anhydride, used in experiments j 4 to 58, was obtained by treating May and Baker's liquid with sodium at room temperatures for 48 hours, filtering off from the sodium acetate, shaking with phosphorus pentoxide for some minutes, filtering and distilling. The collected distillate had B.P. = 137.7-139.2', and its conductivity at 30' was 0.000,002,;65. These comparatively high values for the electrical conductivity of the acetic anhydride probably indicate the presence of some acetic acid, even though the second method of purification is supposed to be efficient.' Aniline and acetic anhydride mix with evolution of heat, and the mixtures are good conductors. A mixture of approximately equal volumes of these two liquids is quite viscous when it cools to room temperatures, and from the solution crystals (acetanilide) readily separate. Such a mixture containing 3 9 . 4 ~ 7wt. ~ of acetic anhydride had a t 30' the conductivity of o.000,573 approximately, indicating that the conductivity-composition curve for these mixtures is similar to that for acetic acid-aniline mixtures, where the conductivity rises to a maximum for some mixture of intermediate composition, ~

1

Walton and Withrow: J. Chem. Soc., 126 11, 2 b 9 (1924)

JAMES ROBERT P O C S D


552

With dilute solutions of aniline in acetic anhydride the electrical conductivities decrease rapidly with time; e.g. a solution with j.iyc wt. of aniline had a conductivity of O . O O O , O O ~ , ~ and I , its conductivity decreased by 8% in 114 hour at 30’. ‘The acetic anhydride alone had k = 0.000,002,76, so that the initial ‘net’ conductivity of the solution was o.ooo,oo1,6 j. Such solutions in a solvent which itself is of high conductivity are unsuited for study. Solutions of acetanilide in acetic anhydride also gave conductivities decreasing with time; e.g+ a 10.3;5% solution of acetanilide in the above acetic anhydride gave k = 0.000,00j,46, decreasing by 1 . 3 ~ 2in 1/4hour a t 30’; the initial ‘net’ conductivity is thus o.ooo,oon,jo. Probably aniline in acetic anhydride quickly gives acetanilide and acetic acid, and then more slowly diacetanilide is formed. K i t h dilute solutions of acetic anhydride in aniline the conductivities do not vary too quickly with the time, and a consistent set of values may be obtained. However the general tendency is for the conductivities of these mixtures to increase with the time: e.g. with mixtures 47, 49! 51 and j8 the conductivities increased by 1.2. 1.5, 6.0and 2 7 C q after 164, 144, IOI and 768 hours’ keeping at room temperatures respectively. The rate and the proportional amount of increase of conductivity are the greatest for the most dilute solutions, the last example being the extreme case observed. The probable chemical actions, when the aniline is in excess, are:-

+ Aniline Acetic acid + Aniline

Acetic anhydride and

-+

-+

+ Acetanilide Acetanilide + Water

Acetic acid

( I) (2)

Action ( 2 ) must be much slower than action ( I ) ; thus with solutions of acetic acid in excess of aniline no evidence of change of conductivity was noticed during the experiments, though doubtless it mould occur after keeping for days. The tables show that the acetic anhydride gives a better conducting solution with aniline than the acetic acid and acetanilide derived from it would give, adding the conductivities due to the latter substances together; either then the effect of the last two substances together, with or without unchanged acetic anhydride, is not additive, or traces of water from action ( 2 ) are rapidly formed, or other actions must he taken into account. Probably additive compounds are first formed between the solvent and solute; and their ionisation determines the initial conductivity, and their subsequent changes the changes of conductivity. Solutions of acetic anhydride in aniline are better conductors than solutions of acetic acid in aniline, comparing either equi-molecular solutions or equivalent, solutions above 0 . ; j normal: below o . i j normal the solutions of acetic acid are the better conductors. But solutions of phthalic acid are hetter conductors than equi-molecular solutions of phthalic anhydride in aniline (v. later). The following densities were obtained for solutions of acetic anhydride, sample ( I ) , in aniline:-

ELECTRICAL C O S D C C T I V I T I E S O F A S I L I N E SOLUTIONS

553

Density 130°/4')

r; wt. of acetic anhydride

anhydride I , 02808

I . 02099 I . 06670


o (Aniline)

I . 01292

Also a solution of acetanilide in aniline, containing 4.73 63 % of acetanilide, had a t 30' the (net) specific conductivity of o . o o o , o o o , ~ o ~ . (4) Solutions of Phthalic Anhydride in

Aniline.

May and Baker's well-crystallised phthalic anhydride was kept in an exhausted desiccator over sulphuric acid for several days before making the solution in aniline. Solution mas effected by gentle warming, say a t 5 0 3 , except that mixture 68 was prepared in the cold, requiring six days at about M x t u r e 68a is about saturated at room temperatures. Aniline and 12'. phthalic acid condense and form phthalanilic acid, Ph.NH .CO.C',H,.CO. OH, then phthalanilide, (Ph . S H . C0)2CoH4,and then phthalanil, PhN/Co\CJI,;

\co/

the first, compound' is formed in twenty minutes at ordi-

nary temperatures. From a solution of phthalic anhydride in aniline, that has been heated to the boiling point, crystals separate on cooling. The various solutions of phthalic anhydride in aniline gave moderately consistent values for their conductivities, which too were unaltered after keeping twelve days at room temperatures. The following densities were determined :% Phthalic anhydrate Density (30'/4') 4.997 0.7305 0

( j ) Solutions

1.03194 I . 01 542 I ,01292

of Phfhalic Acid in AniZine.

blerck's crystalline phthalic acid was dried over calcium chloride and diesolved by gentle warming in the aniline. It did not, dissolve readily. Its solubility was small: the solution with o . ~ ? ;of phthalic acid slomly became turbid even at 30'. This solution had at 30' the density of 1.01496, while the aniline had density of 1 . 0 1 3 2 1 . With solution 7 7 , the conductivity had increased by I!; after keeping for 5 days; in other experiments the increase of conductivity with time was siniilarly slight. (6) Solutions of Phengl-acetic Acid in Aniline. Solutions of well-crystallised phenyl-acetic acid were prepared as with the preceding solids. The 1057 solution was about saturated at 13'. The conductivities were lo^, and they increased with the time of keeping in the cell at 30' bj- I?: or more in I 4 hour. The accuracy of the determinations is therefore moderate: the conductivities of mixtures 8 2 and 83 are higher than those of the others. The solution with 10,034'C of phenl-1-acetic acid had at 30' the density of 1 . 0 2 j 6 9 , n-hile the aniline hac1 the density of 1 . 0 1 2 9 2 . Tingle and Cram: Am. Chern. J., 37, j96 i 1907).


554

JAMES ROBERT POUND

( 7 ) Solutions of Salicylic Acid i n Aniline. These solutions were made from the dried Merck's pure salicylic acid and aniline by gentle warming. The solubility was low. The conductivities were low, and increased somewhat with time-similar to those of the phenyl-acetic a,cid solutions. The mixture 89 was kept in the desiccator a t room temperatures for 11 days before determining its conductivity, but the result seems quite a normal one. The densities of these dilute solutions were assumed from those of similar dilute solutions of phenyl-acetic acid and benzoic acid. ( 8 ) Solutions of Benzoic Acid in Aniline.

Howard's sublimed benzoic acid was dried in an exhausted desiccator over sulphuric acid for several days. The solutions were usually made with the aid of gentle warming. Mixture 141 was made in the cold (12') from the same benzoic acid after resubliming; it took 4 days to dissolve. The mixtures containing much benzoic acid, say 10% and over, were appreciably more viscous than the original aniline. The mixture with 1 8 7 benzoic ~ acid solidified on standing a t IO'; the crystals were probably some aniline benzoate.' The following densities were determined :benzoic acid

14.888 8.676

Density (30°/4') I ,03685 I ,02677

5.0515

I .OZIOO

I . 988

I ,01625

1.01315 The ready solubility of benzoic acid in aniline permits the examinaiion of many mixtures, but unfortunately the electrical conductivities are so low that the experimental errors and the influence of probable impurities, say the slightest traces of water, are large. The lowest,results-presumably the most accurate-are those with mixture 1 4 1 (v. above) and mixture 142, which was made by diluting the former with aniline. Mixtures IOO to 104 gave higher conductivities which were neglected. 0

Solutions of Aniline Hydrochloride in Aniline. Aniline sulphate is not at all soluble even in boiling aniline, and the solution does not conduct appreciably; the concentration of the dissolved salt is probably less than 0 . 0 5 ~ ~ Aniline . hydrochloride, however, is appreciably soluble in aniline; the mixture 135 with 6.38y0of aniline-hydrochloride soiidified entirely on keeping for an hour or eo at 13'; the solid may be some compound2 like 2 An., HCl. The solutions of aniline hydrochloride in aniline are relatively good conductors. There was little or no tendency for the conductivity of these solutions to vary with time; e.g. after 8 days the conductivity of mixture 134, k x 106 = 1 7 . 5 5 , had decreased by less than 0.4%, though the mixture had become a little darker in colour. Merck's pure aniline hydrochloride was used after drying in an desiccator over sulphuric acid for several (9)

Rerthelot: J. Chem. SOC.,53, 1361 (1890). J. Chem. SOC., 120 I, 106 (1921).

* Mandal:

ELECTRICAL CONDUCTIVITIES O F ANILINE SOLUTIONS

555

days. Mixture I 3 3 was made in two days a t room temperature, about zoo, but the other parent mixtures were made by gentle warming. The following densities were found :R wt. of aniline hydrochloride Density (30°/4") Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 24, 2015 | http://pubs.acs.org Publication Date: January 1, 1927 | doi: 10.1021/j150274a009

6.3836

I , 02527

4.3978 0.8zoj 0.2690

I . 01366

0

I

.01300

Mixtures 133 and 134 gave higher conductivities than the others and are not quoted in the tables. Mixtures 135 to 140, the third series, tend to have lower conductivities than the mixtures of the first two series and are probably the most accurate. The concentration of the aniline hydrochloride in grammolecules per lit,re is, of course, also the concentration of hydrochloric acid, assuming that the acid were dissolved in the aniline and subsequently combined with it. Subsequently we shall often refer to these solutions as solutions of hydrochloric acid in aniline.

Solutions 01 Saccharin in Aniline. Saccharin, o-sulpho-benzimide, is easily soluble in warm aniline, and the solutions are relatively good conductors. The best commercial saccharin was dried in an exhausted desiccator over sulphuric acid, and the solutions were made by gentle warming. Saccharin from two different sources was used with no difference in the results; e.g. mixtures 105 to 108,120, and 1 2 1 to 124 were made with sample ( I ) saccharin; mixtures 113 to 119 were made with this saccharin after sublimation; mixtures 109 to I I I were made with sample ( 2 ) saccharin. The parent mixtures 113, 1 2 0 and I Z I were made in the cold within 24 hours. The conductivities of mixtures I 13 and its derivatives were slightly higher than those of the other mixtures; this may be due to the sublimed saccharin being the purest. The mixtures tend to become browner on keeping. Mixtures 105 to I I I were done with one sample of aniline, and mixtures 113 to 124 with another. The conductivities of these mixtures decreased very slightly with time, e.g. the conductivity of 108decreased by 1 7 ~ after 6 days. Mixture I 16 was made from I 14 after a lapse of I I days. The following densities were det,ermined:yc wt. of Saccharin Density (30°/4') (IO)

8.2631

I . 04760

I . 0461 I 1.03884 5.0571

1.03398

2.5663

1.02375 1.01320

0

556

JAMES ROBERT POUND


Discussion of the Results Here we refer to the concentrations of the solutes, c, in gram-molecules per litre a t 30°, the specific conductivities, k , in ohm- cm. units, and the molecular conductivities, A or k, c. The specific conductivity-concentration curves, k-c curves, Fig. I , are in general concave to the k axis, and their

FIG. I

‘steepness’ increases with c. Of course, with completely miscible solutes, like acetic acid in aniline, a t high concentrations the curve has a point of inflexion, bends and reaches a maximum, and thence descends towards the e-axis once more: but we are not concerned with these concentrated solutions here. With our dilute solutions the k-c curves are, in general, concave towards the k-axis throughout, and so that for a certain range of concentration k is! with more or less accuracy, proportional to c, then for a higher range of concentrations proportional t o e*, then to c3, and so on. At low concentrations, c = o to 0.1 approximately, we have k= c, or the k-c graph a straight line, for saccharin, hydrochloric acid (aniline hydrochloride), phthalic acid, phthalic anhydride and salicylic acid in aniline. The k-c straight lines for these solutions do not go through the origin (O,O), but at zero concentration indicate k X 106 = 0.3 approximately. However the behaviour in extremely dilute solutions must be determined by more accurate experiments. With the other five solutions the curve is concave throughout and also apparently goes to the origin. The k-c curve probably goes to the origin for salicylic and phthalic acids also. The k-c curves for the last two substances show a resemblance to the k-c


E L E C T R I C A L COSDUCTIVITIES O F ASILISE SOLUTIOSS

557

curves for solutions of electrolytes in water (v. later). In general the k-c curves do not cross. The order of the curves for the solutions in aniline is as follows, proceeding from the solutions of lowest to those of highePt conductivity :-Benzoic acid. phenylacetic acid, acetic acid, acetic anhydride, phthalic anhydride, salicylic acid, saccharin, hydrochloric acid (aniline hydrochloride), and phthalic acid. Comparative values for the specific conductivities are given below. (The curves for hydrochloric acid and saccharin cross at c = 0.3; and the phthalic anhydride curve at low concentrations cuts the salicylic acid curve, but this part of the phthalic acid curve is perhaps abnormal.) Specific conductivities, k X IO^, for solutions Gm. mol. per

litre

Acrtic acid in aniline

C

Aniline in acetic acid 2

,025

-

.oj

. j?

. I

'5

2 52

1.0

I430

(.08I) 2.55

Salicylic acid

C

Aniline solutions of phthalic anhydride 4 (.55)

9 2.4 4.2

.I

,065

'5

.20

.o

' 5 2

5

3.17

,68

8

.48 ( . 86)

Phthalic acid

1.58 (8.6 __

26.4 Aniline solutions of Benzoic Hydrochloric acid acid

7

.02j

I

Acetic anhydride 3 (.013) (.03I)

9.3 138 __

Saccharin IO 1.7

3.1 7.1

I80

__

Talues in brackets are extrapolated. TABLES Specific electrical conductivities, k , and molecular conductivities, h = k/c, of solutions at 30' containing wyc weight, of solute and of concentration, c gram-molecules of solute per litre at 30'.

7; wt. of

Slolecular Conductivity h x IO$ ( I ) Solutions of Acetic Acid in Aniline (C~H102; mol. K&.= 60.03) :24* 16.375 2.8047 99.27 35,38 25 8.1905 1.3917 j ,804 4.173 26 2.8880 0.4884 0 .jog5 1.043 0.2743 0.1884 0,6866 27 I . 6233 28* 1 2 .j63 30. I9 13.86 2 . I j87 j.8jO 4 . I81 29 8.2317 1.3987 1,8467 2.023 30 5,3841 0.9126 0.6908 I . 2045 31 3.3912 0.5738 0.1835 0.6806 32 1.5955 0.2696

Kumber of

Experiment

Solute

Concentration

\v

0

C

0

Specific Conductivity k X 10'

0,0288

558

JAMES ROBERT POUND

T ~ B L E(Contd.) S NO.

W

C

k X

-4

105

x

105

Solutions of Aniline jn Acetic Acid (C6Hs.NM,; Mol. Wt. = 93.06):14.684 1.695 33* 1.125 9.840 34 6.126 0.69j8 35 9.0685 1.035; 36* 4.890 0.5549 37 2.636 0,2963 38 1.421 0.1592 39 4.2455 0.4795 40* 41 2.0105 0.2254 17.37 7 2 .05


(2)

42* 43 44

0.082

0

0

2.0676 0.5446

0.2319 0 . I 142 0.06086

0

0

1.0205

19.55

84.35 4.57 3.57

0.5228 0.217s 0.

I93

Sotes: ’, after the number of an experiment, denotes that this was a parent mixture, i.e. the mixture was made up from solute and solvent directly, and from which the following mixtures were made by dilntion with solvent. 5 indicates that the conductivity was decreasing with time. I, ” increasing ” ” ,I

(3) Solutions of Acetic Anhydride in Aniline, 102.05:-

46* 47 48* 49

57*

13.156 7.5495 5.907 3 2565 2.7580 I . 50x8 9.663 5.4046 2.968 2.360

58

I .2 4 7 2

jo*

51

54* 55 56

0

0.;580 ,5915 ,3246

74.74 9.836” 4.3” 0.807”

‘2748

o.547’1

,1495 ‘9740 . 5410 .29j8 .23j0

O.Ijj4” 23 ’ 79 3.308” 0.647’’ 0.3830

,1239

0 . I 100”

0

0

2.488

1.991 1.039 24.42

6.115 2.189 I ,630 0.888

o.ozrj

(4) Solutions ofPhthalic Anhydride in Aniline; CsH403;hlol. IVt. 63* 3’139 0.2IjOj 3.875 I . 968” . ‘2455 64 I ,810 1.072/’ ,06635 65 0.9684 I .068” ,06573 66* 0,9574 67 0.3849 .02637 0.537” 68* 0,7305 .OjOIS 0.6890 ,3484 6.061 68a* 4.997 0

12.97 7.286

0.025

=

148.03:17.85 15.80 16.13 16.25 20.37

13.74 17.39

ELECTRICAL CONDUCTIVITIES O F ANILINE SOLUTIONS

559

TABLES (Contd.) C k x IO. h x 108 ( 5 ) Solutions of Phthalic Acid in Aniline; C8H8Oa; Mol. Wt. = 166.05:-

W

SO.

72*


73 76 ”/ I

75* 78 79 80 81

0,4985 0.2600 0.I2895 0.06935 0.3038 0.1530

0.07635 0.04104 0.01734 0

0.03044 ,01587 ,007872 ,00423I ,01855 ,009340 ,004660

0.785’‘ 2.396 1.350 0.8233

119.8 133.8 152.9 185.6 129.I 144.55 176.7

,002505

o.557711

222.7

,001058

0.3278”

309.9

C

3.647 2 . I22

I . 203

0.0275

(6) Solutions of Phenyl-acetic Acid in Aniline; C s H j . CH, . CO? . H ; Mol. \Yt. = 136.06. 0.9285 0.7570 0.703” 69* 10.034 70 6.004 ‘4506 0.327’’ 0.726 j I * 3.036 ,2270 0,1343 0.592 0 0 0.0248 82 * 3.659 0.2739 0 . I 79” 0.650 83 I .629 ,1216 0.0704” 0.579 0

0

(7) Solutions of Salicylic Acid in Aniline; C&

0.0275

(OH) (COOH); 1101.Wt.

=

138.0j.

Sj* 86 87 88* 89 9c* 9I

o.qjo6 0.2516

0.0jZjj

0.03309 ,01847 ,008936 ,04226 ,01348 ,02841 .ooj340

0.6005~~ 0.393 0.246 0.729” 0.319 0 . 53Sf1 0.178

0

0

0.022

0.I 2 1 j

0.5755 0.1837 0.3870

(8) Solutions of Benzoic Acid in Aniline; C 6 H s ,COOH; Mol. Wt. = 92*

I .9882

93*

8.6760

0.16jj 0 ,7300

5.0515

0.4228

95* 96 97

14.888 5.1114 2.6944 18.156 11.224

94 *

98*

99 141“ 142

I . 265 0.4349

0.2248 1.5jog

0.0951 0 . 359511 0.I95C 0.7344 0.2230’’ 0.1087’’ 1.010

0.9488

0.4920

0

0

0.0222

7,035 3.I 768

0.5900 0.26jo

0

0

0.2522

0.1097 0.0235

18.15 21.3 27.55 17.25

23.7 18.85 33.3 122.05.

0.5745 0,4925 0.4612 0.5805 0.5126 0.4839 0.6517 0.5183 0.4275 0.4140


560

JAMES ROBERT POUND

TABLES (Contd.) so. W C k x 103 A x 109 (9) Solutions of Aniline Hydrochloride in Aniline; C8HiN. HC1; Mol. Wt. = 129.53. 109.63 251.I 0.4369 r25* 5 ' 524 126 2.1382 0.1680 20.20 120.2 127 0.8205 0.06425 5.882 91.6 128 0.2690 0.02104 2.160 102.6 129* 4.3978 0,3470 71.37 205'7 130 1.2742 . IO00 9.818 98.2 131 0.5329 ,04173 3.827 91.7 116.5 .or593 I .856 132 0.2035 135*

136 '37 138 I39 140

0

0

6.3836 3'5629 I .8240 0.9937 0,3820 0.1381

0.5054

0

0.020

0.2808

45.30

279.0 161.3

0.I432

15.07

105. 2

0.07783

0.02990 0.01081 0

141.0

Solutions of Saccharin in Aniline; C 7 H 5 0 3 S S1201. ; Wt. 7.9571 0,4543 132.03 I 06 j.oj;1 '2857 45.77 107 2.5663 ,1435 12.42 IO8 I . 2848 ,07146 4.674 109* 5,0942 ,2875 44,3I I10 2.8995 ,16245 14.33 111 1 . 0579 .0j881 3.674 IOj*

0

0

0.472;

116

8.2631 2.9939 1.4644

117

0.7458

118

0.331' 0.06616

114

I

I9

I20*

I . 0103

I2I*

1.4094

I22

123

0,6468 0.2597

121

0.104oj 0

=

183.11. 290,6 160.3 86.6 65.4 154.1 88.2 62.j

0.020

.16;;5

0

117.4

0.023

(IO)

113*

88.4 90.2

6.879 2.696 I . 269

164.5 17.22

,08154

5 283

.o4136 ,01832 ,00366 .os616 ,07843 ,03590

2.528

'

348.0 102.6 64.8 61.1

1.291

7 0 ,j

0.4525

123.6 65.8 69.6 65.9 80.3 I09,9

3,694 j . 461

2.367

,01437

1,153

,005756

0.632j 0 , 0 2 0

In general, the molecular conductivity, d,rises increa-ingly rapidly with increasing concentration. A t low Concentrations, c = .os to .I, A often reaches a minimum, and then at lower concentrations h rises with decreasing

561


ELECTRICAL COKDGCTIVITIES O F ANILINE SOLUTIOSS

concentration; such ie the case with the aniline hydrochloride and saccharin solutions. With phthalic and salicylic acids we can deal only with low concentrations, and here throughout the A-c curves fall with increasing concentration. Thus with these two acids dissolved in aniline we have an approach to the behaviour of weak electrolytes, like acetic acid, in aqueous solutions. There is, however, no definite limiting molecular conductivity at zero concentration, as the A-c curve is asymptotic to the A-axis. For the curves that rise to some value of Ao,however indefinite, at zero concentration we have the following more or less probable values of A:-phthalic acid, 400-600; saccharin, 160; hydrochloric acid, 160; salicylic acid, jo. With pht'halic anhydride and benzoic acid the A-c curve is doubtful at low concentrations; the experimental errors are here too large. With the other solutions the A-c curve, in the absence of more accurate data, falls throughout to the limiting values,for acetic acid, 0 . 3 5 ; acetic anhydride, 0.5; phenylacetic acid, 0.4j;and for aniline in acetic acid probably zero. In these solutions, for which A falls with decreasing concentration, the nature of the ionisation, etc., must be vastly different from the conditions holding in aqueous solutions. Also in the former solutions the significance of -io, if it is ot'her than zero, must be different from that usually accepted for A, in aqueous solutions, where t'he maximum value, A,, is held to indicate complete ionisation. We endeavoured to eee whether the mass-action law held for these solutions. If we suppose a binary electrolyte, ionising as AB 3 A+ B-, and let c = the concentration of the original electrolyte AB and y = the degree of ionisation, then if the mass-action law holds klc(1 - y) = k&*. In the usual consideration of aqueous solutions we put y = A!A,, and deduce that I 'A = (I/aAz0)(CA) I / & , where a = the ionisation constant = kl/k2; whence I / A is a linear function of (CA) or k (the specific conductivity). I t is, however, not necessary to consider the value of A, in order to test this relationship. For k is proportional to c, the ion concentration, or y = k/dc, k2 where d is a constant; then the mass-action equation leads to ___ d(dc - k)

+

+

C

I

the ionisation constant, a ; whence -- = - k k ad2

+ 5, which is the same relation d

as found before. I t is necessary to note this, for in the present solutions the functions A, and A,/.i, have little or no significance. We have tested the agreement of our data with this equation. We find that for aniline in acetic acid and for acetic acid, acetic anhydride and phenylacetic acid in aniline the c, k-k curve is hyperbolic and asymptotic to both axes. For phthalic and salicylic acids in aniline this curve is concave to the k-axis and approaches the c/k axis asymptotically; probably here the mass-action law holds approximately for very dilute solutions. With hydrochloric acid and saccharin in aniline the curve is a compound of the above types; as k decreases, c/k rises till it reaches a maximum value, after which it decreases again as for phthalic acid. For OUT solutions the mass-action law holds, if at all, over a very low range of concentrations indeed.

JAMES ROBERT POUND

562

We then tested the applicability of the Kraus and Bray equation for electrolytes where the ionisation is low, i.e. cA2 = P(cA)" or k2/c = Pk", where P and vi are c0nstants.l From this equation we have log k2/c = m. log k log P. For hydrochloric acid in aniline and for aniline in acetic acid we found that the graph of log (k2/c) against log k was roughly a straight line. But on working back from this line to values of k from given values of c, we found that the calculated values agreed only approximately with the observed values. For example, with aniline in acetic acid the constants mere m = 1.63 j and P = 14.4j, and the average deviation of the calculated values of k from the observed values of k was -4Yc; the Kraus and Bray equation was only an average equation over the range c = 1.1 to 0 . 2 . Similar results held for solutions of hydrochloric acid in aniline. Quite as good results may be obtained from a relation like k = x(y - c ) " , where r , y and n are constants: or, for example, for most of our solutions of hydrochloric acid in aniline by the equation k = 538 c2 - 4)over the range of c = 0.5 to 0.1. The plotting of complex functions, especially those involving logarithms, is liable to become quite misleading, if the errors introduced in obtaining those functions (and logarithms) are not allowed for.


+

The Kraus and Bray relationship reduces to k2-" = p.c, or k = q.cp, where q and p are constants, and thus log k = p. log c log q. It is simpler to try the graph log k-log c than the graph of log (k2/c)-log k. For none of our solutions in this graph log k-log c a straight line over the whole range of the experiments, except perhaps for phthalic anhydride, for which substances however the results are not of the highest accuracy. For the aniline solutions of phthalic and salicylic acids and perhaps of acetic anhydride, the log k-log c graph is a straight line over a range of the lowest, concentrations; over these concentrations therefore the Kraus-Bray modified equation holds. In general the log k-log c curves are concave to the log k axis, Le. log k increases faster than log c; for solutions of aniline in acetic acid the reverse holds.

+

It is clear that the relations between k and c for various electrolytic solutions are not covered by any simple extensions of the law of mass-action for any considerable ranges of concentrations. We may write provisionally that k = q. cp, where q is a constant and p i s some function of c. If the form of the function p is the same for all electrolytes, then the constants there involved must alter greatly. For solutions of salts in water, p < I , and the k/c curve approaches the zero asymptotically to the k-axis; and for many non-aqueous solutions p > I , and the k/c curve approachee zero asymptotically to the c-axis. Even then one such equation can only hold for one eleckrolyte from zero to moderate concentrations, as a k/c curve usually exhibits a maximum a t a certain value of c. The connection between k and c must indeed involve the reasons for ionisation and the relations between the ions and the solvent and the relatione between the ions themselves. Iiraus: loc. cit., p. 75. 2

Kraus: Ioc. cit., p. 79.


ELECTRICAL CONDUCTIVITIES O F ANILlXE SOLUTIONS

563

Summary Solutions in aniline are relatively poor conductors of electricity. The conducting solutions behave generally like typical non-aqueous electrolytic soluti om. Thus the specific conductivities rise so rapidly with increasing concentration of solute, that the molecular conductivities also rise rapidly with increasing concentrations. KOsimple equation was found to express the relations between the specific conductivity, k , and the concentration of solute, c. Evidently k=q.cP, where p , a t least, is some function of c. At very low concentrations some solutions in aniline behave like aqueous solutions and the molecular conductivity rises to a limit at zero concentration; more delicate experiments might extend the number of these solutions. The stronger acids with aniline give solutions of which the conductivities tend to increase with the time. Assuming the initial conductivity is due t o the formation of aniline salt, the subsequent formation of aniline and liberation of water will explain the increase of conductivity. The School of Mines, Bnllarat. 17wtor?a, dustralaa January 24) 1924.

The Electrical Conductivities of Some Solutions in Aniline - The

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