2352
ARTHUR B. LAMB ANI) VIC‘I!OR YNGm.
sodium hydroxide, and sulfuric acid have been determined. The curves showing the heat of coagulation as a function of the purity vary widely in shape with the nature of the coagulant, the heat effect being usually positive, but with sodium sulfate and sodium chloride at low purities, negative. As the purity increases the heat of coagulation becomes smaller, finally becoming negligible, except in the case of sulfuric acid. The peculiar behavior of the last electrolyte is due to solution of the ferric oxide. 5. When the heat of coagulation is plotted against the concentration of the coagulating electrolyte, smooth curves are obtained showing no “break” at the point of limiting concentration. 6. The heat effects observed on coagulating ferric oxide sols with electrolytes are to be attributed to the action of the electrolytes in the coagulants upon the electrolytes, particularly ferric chloride, present in the sol. The change in dispersity of the ferric oxide on coagulation does not involve a heat change greater than 1to 2 calories per gram equivalent of ferric oxide. 7. In the case of ferric oxide hydrosol there exists no “heat of peptization” analogous to the heat of solution of crystalloids. The work described in this paper has been carried out with the assistance of a fellowship established by E. I. duPont de Nemours and Company, to whom the authors wish to express their indebtedness. MADISON,WISCONSIN. [CONTRII~UTION FROM THE CHEMICAL LABORATORY OF
HARVARD UNIVERSITY. ]
THE STRENGTHS OF COBALTAMMINE BASES AND WERNER’S THEORY OF BASES. BY ARTEUR3. LAMBAND VICTOR YNGVE. Received July 20, 1921.
The great strength of many cobaltammine bases has attracted the attention and evoked the surprise of investigators in this field. Cobaltic hexammine hydroxide (luteo cobaltic hydroxide), for instance, is a very soluble, deliquescent substance whose solution is caustic in its properties, absorbs carbon dioxide with avidity, and displaces both ammonia and silver oxide from their salts. Werner, estimating the strengths of various ammine bases qualitatively from their chemical behavior and from the properties of their salts, has arranged certain of them in the order of their strengths, and indeed largely on the basis of these considerations has proposed a new theory of bases and of hydrolysis. We have therefore been interested to obtain quantitative measurements of the strengths of these bases. We have used the conductivity method for this purpose, measuring the conductivities of their dilute solutions a t various concentrations and comparing the resulting molecular conductivities with the conductiv1
Werner, “Neuere Anschauungen,” 3rd edition, Braunschweig, 1913, p. 265.
STRENGTI-XS OF COBALTAMMINE BASES.
2353
ities at infinite dilution, as computed from measurements of the conductivities of salts derived from them. Slolutions of the bases were prepared by triturating their bromides with a n excess of moist silver oxide, the mortar, pestle, silver oxide and water having all. been carefully cooled to zero degrees. The solution was then rapidly filtered by suction into a graduated 25Occ. flask, the residue washed several times with 1Occ. portions of ice-cold water, and the solution made up l o the mark. After thorough mixing, a portion was transferred to conductivity cells and the conductivity measured, first in an ice-'bath and then in a 25" thermostat. Aliquot portions of the original solution were diluted sticcessively and lower concentrations were then measured in the same way. The more important details of manipulation were as follows. of Materials.-The water was prepared by redistillation using a ~~~~~~~~~~~
little barium hydroxide and potassium permanganate. It and the solutions made from it wtre kept in carefully closed and steam-extracted resistance-glass bottles. I t s condiictivit y was always measured before use. Most of the ammines were prepared according to the improved methods of Jiirgensen.2 The hexammine bromide was, however, made by precipitation with pure conc. hydrcibromic acid of hexammine chloride prepared according to the method of Lamb and 1,arson.s It was then washed several times with dil. hydrobromic acid and with alcohol until aU. the acid was removed, and finally was dried in an air-bath at 35". The triethylenediamine bromide was prepared from the hexammine bromide according to the method of Pfeiffer,4 while the dibromo-diethylenediamine bromide, which on treatmcnt with moist silver oxide gave diaquo-diethylenediamine cobaltic hydroxide was a commercial product. T h e silver oxide was prepared by the action of a clear solution of barium hydroxide on an excess of silver nitrate in dilute solution. It was washed with a large amount of conduetivity water until no test for barium ion could be obtained. It was kept under c ~ n d ~ e water t ~ v in~ a~ closed ~ vessel. The Apparatus.-Three of the conductivity cells were flask-shaped vessels of Jena ,glass, provided with large strongly anchored sealed-in electrodes; one consisted of dip electrodes fitted into a widemouthed flask. ]Each was closed by a rubber stopper and was provided with a thermometer legible to 0 01'. A large ice-bath served for a 0' thermostat, and the water thermostat maintained a temperature of 24.96" constant to within 0.01'. The true temperatures were established by a calibrated thermometer whose ice-point was carefully checked. The constants of the cells were fixed 1y, means of a solution of potassium chloride made up by weight t o 0.019894 molar using the density data of Baxter,6 and taking the conductivity of this solution as O.OiD22759 mhos a t 24.98'. The constants were redetermined a t the end of our measinremeints and faund t o be identical with the initial values. The slidewire bridge could be read t o one part in 5000 and was carefully calibrated under the conditions of its use. No readings were taken until the contents of the cells had reached precisely the temperature of the thermostat. Successive bridge readings were in most cases Jorgensen, Z. anorg. Chew, 17, 455-9 (1898). Lamb and Larson, THISJOURNAL, 42, 2025 (1920). l?feiffer, Ann., 346, 59 (1906). 5 Baxter et at., '&IS JOURNAL, 33, 913 (1911). 2
2354
.
ARTHUR B LAMB AND VICTOR YNGVE
constant t o within the accuracy of a setting, and the mean of several readings was recorded. I n the case of the dinitro-tetrammine salts, however, a slow decrease in conductivity was noticeable a t 25', while with the carbonato-tetrammine this change was noticeable a t 0' and so rapid at 26' as t o make measurements of little value. In these latter cases the measurements were made over a period of 2 or 3 hours, and extrapolated to zero time.
The Water Correction. The correction of our conductivity measurements for the conductivity of the water is of considerable and unusual importance. This is due to the fact that the conductivity of the water, and indeed of any carefully purified water distilled in vessels open to the air is substantially that of the carbonic acid dissolved in it.s In acid or neutral solutions the corrections on this account are of no specid importance, but here this carbonic acid will neutralize an equivalent quantity of the base and, as the net effect of this is to replace a swift, hydroxyl ion for a sluggish, carbonate ion, a considerable correction, a t least in dilute solutions, must be applied. Calling CIIacOt the total concentration of the carbonic acid, this correction will be A =
2 XOH--
xCOa--
1000
CRZCOt
where XOH- and XcoP-- are the conductivities of the hydroxyl and carbonate ions at the temperature of the measurements. Since the specific conductivity of a solution of carbon dioxide is proportional to the square root of the partial pressure of carbon dioxide, and since carbon dioxide is only slightly dissociated even a t these concentrations, the specific conductivity must also be proportional to the square root of its total concentration. A solution whose total concentration of carbon dioxide is 2.94 X lop6mols has a specific conductivity of 0.65 X mhos a t O O . 7 Therefore, calling LOthe specific conductivity of the water lo-' =6.8 X 107L02;and therefore A $ = a t O", C H z ~ 0 , = L ~2'94 2 0.65 X lo-* 8.3X 108Lo2;and A2a0 = 2.82 X 10' Lo2mhos. These corrections a t 0' and 25 O have been applied to the specific conductivities a t concentrations down to 0.00666 M , and since LOvaried between 0.94 and 1.48 X lo-" mhos, the correction varied between 0.73 and 1.8 X loT6a t 0" and 2.5 and 6.2 X mhos a t 25". This method of correction is rigorous enough a t these concentrations. At still lower concentrations the question arises whether the second hydrogen of carbonic acid is sufficiently ionized to react completely with the hydroxyl ions. Kendall, THISJOURNAL, 39,7 (1917). Kendall, {bid., 38, 1494-5 (1916).
STRGNGTHS OF COBALTAMMXNE BASES.
2355
If only the first hydrogen were neutralized the decrease in the specific c o ~ ~ ~ u cwould t ~ y bes ~t~ Ai,. = ~XON--XICO~-)OOCH~CO, = 0.080 C N ~ mhos; C ~ ~ and similarly A& = 0.146 C B mhos. ~ ~If the ~ second ~ hydrogen were then neutralized, the further decrease would be AC~=0.042 C H ~ and C ~ ~A ; r s O = 0.0741 CN,CrJ,.
The extent to which these neutralizations will occur can be computed from the ionization constants of carbonic acid and oi water. The ionization constant oi the first hydrogen of carbonic acid is K ~ = 2 . 2 4 X l 0 - ~ a t 0"and 3.5 X IO-' a t 25°;9 that of thesecondisKz=G ;< 10-llat 1 8 O . I 0 It is evident that a t the concentration of hydroxyl ion under consideration (0.00131M i the neutralization of the first hydrogen ion may be considered as complete. The neutralization of the second hydrogen will be determined by the equilibrium equations CEI+XCOH= SH~O, and
CH + x cco,--
=K2,
CHCOs-
where SNIorepresents the ion product of water. Calling C ~ H the initial concentration of hydroxyl ion, that is, its concentration after the compiete neutralization of the first hydrogen of carbonic acid, x the number s the second hydrogen neutralized, and y the number of mols of of m ~ l of carbonate ion formed a t equilibrium, CH+=y-x and COH--.C&---X. Then (y--x)(C&- -x) =SI-I~O; and ( y - x X ) y = l i i ( C ~ ~ c o ~ - ~ ) . The solution of these two equations gives a third degree equation. It is thereiore much simpler to solve them by a process of approximation for each set of values of the constants, first guessing a value of y , then solving each equation for x,and finally varying y until each equation gives an identical value for x. After a few trials this solution can be made very rapidly. Values of y computed in this way for CH2cOa= 1.18 X M , and for a series of hydroxyl-ion concentrations a t 25" are given in Table 1. These values of y divided by CH~CO~ give the fraction of the total carbonic acid converted into the carbonate ion; that is, the fraction fully neutralized. The resulting figures are entered in the fourth column of Table I. Similar computations were made for the other concentrations 8 For the conductivity of HCOa- see Kendall, THIS JOURNAL, 38, 14.89 (1916). Kendall, ibid.> 38, 1486 (1926). Johnston, ibid., 37,2004 (2915). BlcCoy, Am. Chem. J., 29, 437 (1903). \rValker and Cormack, J . Chem. SOC.,77, 8 (1900). Shields, 2. physik. Chem., 12, 167 (1893). Auerbaeh and Pick, Arbeiten kais. Gesundhdtsamt., 38, 243 (1911). Prideaux, Proc. Roy.Soc., 9lA, 535 (1915).
2356
ARTHUR B. LAMB AND VICTOR YNGVB.
of carbonic acid. Values for intermediate concentrations of hydroxyl ions were found by graphical interpolation. TABLEI. IONCONCENTKATIONS. [ C H ~ C O 1.18 ~ = X lo-*. Temperature = 25O.I Initial conc. O H - X loa&?.
6.67 1 33 0 667 0.218 0.133
cbH- X 10SM.
6.54 1.21 0.549 0.100 0 016
CCOI--O~Y
ccos--.
XlOa.
CHZCO,
0.115
0.97 0.87 0 74 0 28 0 055
0.103 0 087 0 033 0 0064
It can be seen from this table that the neutralization is nearly complete at the highest concentrations, and corrections for this effect were therefore only applied a t concentrations of 0.0013 M and below. With water of 0.9 - 1.4 X mhos) the total correction for water the purity used (LO= is, however, very large at the lowest concentration, so that any correction is unsatisfactory. This is shown by the large values of the water correction expressed as percentages of the total conductivity ( A/L) in the tables of data. In any attempt to secure more accurate values for low concentrations much purer water should be used. Correction for the Solubility of Silver Oxide.-During trituration of the cobaltammine bromide with silver oxide, and the subsequent washing some silver must dissolve, and thus contaminate the solution of the cobaltammine hydroxide. The amount of this contamination can be determined from the known solubility of silver oxide. The total solubility of silver hydroxide is 2.16 X mols per liter a t 2 5 O , according to the careful and direct measurements of Noyes and Kohr.ll The ion concentration of the saturated solution is 1.23 and 1.39 X mols a t 20' and 2b0, respectively, according to Bottger.I2 Assuming that the total solubility has the same temperature coefficient as the ion concentration, it will equal 8 X 10-6 mols a t 0". The total volume of water used during trituration and washing may be taken as 50 cc., and Noyes and Kohr, 2. fihysik. Chem., 42,338 (1903). Bottger, 2. physik. Chem., 46, 602 (1903). It should be pointed out that BGttger's Tialues are somewhat too large for silver hydroxide and lead hydroxide, as he corrected the conductivity of their solutions by simply subtracting the conductivity of the water. This neglects the fact that the carbonic acid which is chiefly responsible for the conductivity of the water will have its first hydrogen completely neutralized, and will therefore have a higher conductivity than when slightly dissociated in the original water. The correction, A', for this effect will evidently be l1
12
For the water which he used CH~CO, = 2.8 X and therefore A i b o = 3.1 X 10-o and Ai09 = 2.8 X mhos. These corrections, applied t o Bottger's values for the ion concentration give, for 25' and 20°, respectively, 1-39 and 1.23 X 10-4 M.
235'1
STRGNG'I'HS OF COBAL'I'AMMINB BASBS.
a ~ ~ u its ~ ~complete n g saturation and the complete dissociation of the silver- hydroxide, the concentration of silver ion would be 1.6 X 10-8 Ad. Thi~,amount of contamination is wholly negligible in the 3300 X A4 solutions which were chiefly studied, and practically negligible in the few M solutions. No correction has, therefore, been applied to our results for this effect.
The Conductivity Data. The conductivity data are collected in the following tables. X and a signify molecular Conductivity and percentage dissociation as usual, LO, the specific conductivity a t 0" of the water used; A/L, the percentage of thle total conductivity which the water correction represents a t the various concentrations, and R the molecular conductivity of the hydroxide obtained by subtracting the conductivity of the neutral salt from the observed values. TABLEPI. HEXAMMINB COBALTIC BROMIDE. Lo 1.35 X 10-8 mhos. ago.
LOO.
Cone.
MXPO~.
1.
Observed.
2.
1.
%.
'25 Observed.
'.
2.
a26 O,
Mean.
Calc.
n=1.45. %.
173.3 58.6 319.1 319.1 319.1 319.9 57.6 217.4 72.5 397.0 397.0 397.0 397.9 77 1 251.0 85.4 462.0 461.8 461.9 460.1 83.4 273.1 91.6 502.6 502 4 502.5 502.2 90.6 a (297.1) (553 .5) TABLE1x1. ~ ~ COBALTIC x DIBROMIDE ~ HYDROXIDE. ~ MHEXAMMINE ~ COBALTI ~ c BROMIDE ~ DIHYDROXIDE. Lo = 1.48 X I O d mhos. R. a. R. a. Conc. A. A. 00. 25'. 00. 250. 0 0. 250. M x 103. 00. 250. 0'~ 25'. 0'. 2.5'. %. %. %. %. 33.23 216.9 388.4 101 175 63 58 258.2 449.4 200 348 63 57 6.562 259.5 463.8 116 199 72 66 302.3 529.0 230 397 72 66 1,836 293.8 528.8 125 221 78 73 344.0 603.4 260 448 81 74 0.:26'8 333.6 621.0 152 286 95 95 387.2 693.2 296 526 93 87 33.23 6.662 1.336 0.2678
174.1 215.3 253.8 272.1
174.1 215.2 253.8 272.1
Calc.
Mean. n-1.48.
174.1 215.3 253.7 272.1
0 TABLE
Iv.
HEXAMMINE COBALTICHYDROXIDE. LO = 1.48 X 10-6 mhos.
h' mhos. Conc. a!! x 103.
Obs.
33.23
347.5 396.9 431.1 469.0
6.662 3..336 0.2678 ID
X2.50 mhos.
Calc. tZE1.4.
aoo.
347.5 396.8 431.6 460.7 (482.0)
72.2 82.4 89.5 97.4
Obs.
%.
591.3 675.3 739.0 813.0
Calc. n-1.3.
ago.
%.
%.
589.9 672.7 741.8 791.8 (901 .0)
65.5 74.8 81.8 93.4
0.2 0.7 3.2 14.0
A/L.
2358
ARTHUR B. LAMB AND VICTOR YNGVE.
TABLEV. AQUO-PENTAMMINE COBALTIC HYDROXIDE. Lo = 1.31 X mhos. mhos.
Obs.'O".
Conc.
M X 108. 33.21 6.66 1.335 0 ,2683 0
ff
Calc.
223.9 244.6 265.5 285.7 (475.0)
223.4 244.7 261.8 286.8
00.
A/L.
("00.
7%. 45.7 50 .O 53.5 58.6
n = l . 11.
%.
%.
0.2 1 .I 4.1 17.5
70.8 77.9 82.9 90.7
TABLEVI. DIAQUO-TETRAMMINE COBALTIC HYDROXIDE. Lo = 1.04 X 10-G mhos. ff0".
%.
ff'00.
mhos.
116.4 115.4 102.7 (469 0)
24.8 24.6 21.8
74.7 74.0 65.9
Conc.
M X 108. 6.59 1.321 0.265 0
.
A/L.
%.
%.
2.5 6 .O 31.3
TABLE VII. TRIETHYLENEDIAMINE COBALTIC HYDROXIDE. L o = 1.34 X 10-6 mhos.
33.29 6.674 1.338 0.2683 0
304.2 344.0 375.4 394.4
A250mhos. Calc.
a
mhos. Calc. n=l.37.
Obs.
Conc. M XlO*.
00.
%.
303.0 344.5 374.5 394.6 (423.6)
cy
Obs.
n-1.35.
67.0 81.2 88.6 93.1
519.1 596.4 651.6 706.8
512.3 594.5 659.6 705.5 (781 .O)
25'.
A/L.
%.
%.
66.4 76.3 83.3 90.4
0.2 0.7 2.8 12.7
TABLE VIII. DIAQUO-DIETHYLENEDIAMINE COBALTIC HYDROXIDE. LO = 1.34 X 10-6 mhos. Conc.
M X 108. 33.29 6.674 1.338 0.2683
0
?Jo.
%e.
01'00.
mhos.
%.
%.
107.6 113.9 116.8 143.1 (430 .O)
24.6 26.6 27.3 33.4
73.7 79.8 81.8 100.3
'25". mhos.
185.0 197.4 209.0 269.4 (778 .5)
25'.
A/L.
22.7 25.2 26.7 34.5
0.4 2.0 9.0 33.5
%.
%.
TABLEIX. CARBONATO-TETRAMMINE COBALTIC HYDROXIDE. Lo = 1.04 X 10-6 mhos. Conc.
M X 108. 33.32 6.674 1.338 0.2683 0
a AOO.
mhos.
108.7 113.4 119.0 100.3 (121.8)
00.
%. 89.2 93 .I
97 '6 85.3
A/L.
%.
0.3 5.7 24.0
2359
S'I'RENGTHS 01 COBALTAMMING RASES.
TABLEX. 1,2-DINITRo-rETKAWMIE COBALTIC HYDROXIDE. Lo = 0.94 X 10-emhos. ff
cone.
x
M
xOa.
101.
ti .657 1.335 0.2676 0
00.
mhos.
%.
102.5 99.9 102.8 (123.1)
83.3 81.2 84.7
x250. mhos.
176.8 179 .O 201.8 (228.3)
a!
250.
A/L
%.
%.
79.2 78.4 89 ..a
1.1 5.4 21 .0
TABLEXI. 3,6-DINITRO-TETRAMMINE COBALTIC HYDROXIDE, LO = 0.94 X 10-6 mhos. Conc.
M x 108. ff .329
0.6675 0.1339 0
xO 0.
a
0 0.
mhos.
%.
116.2 117.2 123.2 (122.9)
94.6 95.4 100.3
x2ao.
mhos.
201.4 209.0 256.0 (228.1)
a!
26 0"
A/L.
88.3 91.6 112.2
1.9 9 .o 30.3
%.
%.
TABLE XII. DINITRo-AQUO-TRL4MMINE COBALTIC HYDROXIDE. LO = 0.94 X 10-8mhos. M
ff
Conc. x 10'.
AOO.
5.413 1.085 0.2196 6)
0 0.
x2so.
a!
250.
mhos.
%.
mhos.
%.
52.4 48.6 54.2 (134.5)
39.0 36.0 40 .0
92.1 90 "2 120 .0 (251 3)
37.0 36.0 48 .0
A/L,
%.
5.4 13.7 48.0
I n view of Werner's conclusion13 that in alkaline solutions of the ammines hydraxo compounds are present in equilibrium with the aquo hydroxi'de we have computed from the observed conductivities of all the aquo hydroxides the percentage ionization of the remaining hydroxide, assuming that all of the complexly bound water has been replaced by hydroxyl groups. The results obtained are collected in the columns headed a',p in the above tables. The Conductivities at Zero Concentration. The conductivities a t zero concentration, required to compute the degree of ionization, can, in the case of the most highly ionized bases, be com-
puted with considerable certainty from the actually observed conductivities; but in other cases and in general, on account of the serious effect of dissolved carbonic acid on conductivity measurements of bases, it is advantageous to compute these conductivities from measurements of the eontluctivities of salts of these bases. This i s the method we have adopted. In most cases the necessary data were found in the literature. The values adopted for the conductivities of the various anions ueed in these comla
Werner, Ref. I, p. 264.
2360
ARTHUR B. LAMB AND VICTOR UNGW.
putations, l4 and the resulting conductivities of the various cobaltammine ions are collected in Table XIII. TABLE XIII. CONDUCTIVITIES OP Cobaltammiiie cations.
"HI3
VARIOUS COBALTAMMINE IONS. Anions.
A. 0 0.
mhos.
167.0 160.0 154.0 108.6 115.0 16,8 18.1 17.9 29.5
250.
mhos. 327.0 314.0 300 .O 205.5 219 .O 33.8 36.3 36.1 59.6
A. 0 0.
mhos.
Brc1OHNO; HCO; co f
43 . I 41.1 105.0 40.4 25,O 88 . 0
25'.
mhos. 75.6 75,5 192.8 10.6 46.2 166.4
Hexamwine Cobaltic Ion.-Although numerous measurements of the conductivity of hexammine salts have been made by Werner and Miolati16 and Werner and Herty1l6the results are discordant and much lower than those obtained more recently for the chloride by Harkins, Hall and Roberts.'? We have, therefore, measured the conductivity of hexammine bromide a t both 0" and 2zoI and the results are collected in Table 11. Values for the conductivity a t zero concentration have been obtained by the wellknown method,18 based on the Storch-Bancroft equation, of plotting 1 / X against (CX) n - l and varying n until the points lie as closely as possible to a straight line. The values of the exponent and the limiting conductivities thus obtained and of the molar conductivities computed inversely from them are included in the table. The close agreement of the computed and observed conductivities indicates the probable reliability of the extrapolation. The data of Harkins, Hall and Roberts on the chloride have been computed in a similar fashion; satisfactory concordance was obtained using n = 1.50 and 1.48 a t 0" and 25", respectively; giving 165.2 and 326.7 mhos for the conductivity of the hexammine ion, as compared with the 167.8 and 327.3 mhos which we obtained above from our measurements on the bromide. We have, therefore] adopted 167 and 327 mhos for our further computations. The reliability of these values is further attested by the close agreement of the conductivities of the hydroxide computed from them with the observed conductivities (Table IV) . 14See Johnston, THISJOURNAL, 31, 1015 (1909); and Landolt u. Bornstein, "Tabellen." 16 Werner and Miolati, 2. physib. Chem., 12, 41 (1893); 14, 511 (1894); 21, 237 (1896). Werner and Herty, 2. physik. Chem., 38, 336 (1901). t7 Harkins, Hall and Roberts, THISJOURNAL, 38, 2656 (1916). I* See Noyes and Coolidge, Carnegie Inst., Pub., 63, p. 50.
STRGNOPHS OF COBALTAMMINE BASES.
2361
~ ~ ~ o - ~ ~ ~ ~and t a Biaquo-telramwinc m m ~ n e Ions.--The conductivities ob' various salts of these ions have been measured a t 25" by Werner and
~ ~ ~ ~ [ o ~ These a t i . ? measurements $ have shown that the aquo-pentarnmine and the diaqtio-tetrammine salts h a w conductivities 12 and 25 mltos s m d e r than the hexammine ion at 0.0005 M concentration. We have, therefore, adopted 160 and 154 at 0" and 314 and 300 mhos a t 25" for these valtres. Sriethylenediawi7
