PERIODIC ACID AND PERIODATES. I1
THESYSTEM SILVER OXIDE-PERIODIC ACID-WATER
AT
35°C '
P. P. GYANI Science College, Patna 6 , India Received October 18, lS@ INTRODUCTION
A large number 01 salts of periodic acid have been prepared (9). Among them the silver salts have received special attention, probably because they are obtained as intermediate compounds in the preparation of periodic acid (10, 17). Attempts have also been made to study the properties of the silver periodates, especially the physical properties, such as density, solubility, heat capacity, magnetic susceptibility, dielectric properties, etc. (2, 5, 13, 15, 16). In spite of numerous attempts to determine their compositions and formulas there is still scope for doubt. The methods so far employed for the investigation of these salts have almost invariably been vague in some respects. The conditions, such as temperature and concentration, under which the different salts mere formed have not been exactly defined. Ammermuller and Magnus (1) obtained the salt AgI04 by evaporating a solution of silver dimesoperiodate in warin nitric acid. Rammelsberg (11) obtained Ag310s by treating Ag41209.3H20with silver nitrate in the cold. IGmmins (8) obtained a silver salt, which he represented as Ag41~09.3H20,by treating AgIO4 with warm water. Similarly, the strengths of solutions used for the preparation of the salts have, not infrequently, been described as merely dilute or strong. Thus, Kimmins (8) obtained the salt Ag41209.3H20 by treating with silver nitrate a solution of sodium periodate dissolved in a slight excess of nitric acid. He prepared a different salt, Ag3HJOo, by the same method but by using a moderate excess of nitric acid. Cnder such indefinite conditions of preparation the possibility of mixtures being regarded as pure compounds is by no means excluded. Slight modifications in the conditions of preparation'have given rise to salts which differ in their analyses and on that evidence alone various formulas have been assigned to them. It therefore seemed worthwhile to carry out a systematic study of the silver salts of periodic acid under exactly defined conditions of temperature and concentration. The present work forms a complete study of the three-component system silver oxide-periodic acid-water at 35°C. In contrast to previous work such a study eliminates the presence of nitric acid, whose concentration appears to influence the nature of the salt formed (8). The presence of sodium and potassium salts in the preparation mixture is also avoided. Hence this line of work should be able at least to detect the compounds existing at the particular temperature selected as far as salts crystallizing from aqueous solution are concerned. This work constitutes a portion of the thesis &bmitted by the author in partial fulfillment of t h e requirements for the Ph.D. degree, Patna University, 1948. 1111
1112
P. P. GYANI EXPERIMENTAL
Silver oxide was prepared by adding a dilute solution of Merck's pure sodium hydroxide in carbon dioxide-free water to a solution of pure silver nitrate. The precipitate obtained was washed thoroughly with boiling water until free from alkali. It was dried and stored over quicklime. Silver oxide thus prepared did not show any trace of carbonate. Estimation of silver as silver chloride showed the sample to be 99.6 per cent pure AgsO. Periodic acid was prepared BS described by Booth (3). Sodium iodate, obtained by the action of iodine on sodium chlorate, was oxidized to periodate in alkaline solution by means of potassium persulfate. The sodium periodate was converted into barium perid a t e by reaction with barium nitrate. Periodic acid was subsequently liberated from the barium periodate by treatment with concentrated nitric acid. The solution, on concentration under reduced pressure, gave colorless crystals of periodic acid. Various mixtures were made up by taking approximately weighed quantities of silver oxide and periodic acid and measured volumes of water in varying proportions. Each mixture was introduced into a 50-ml. test tube of Pyrex glass placed in a water thermostat at 35°C. f 0.1'. The mixture was stirred by means of an electrically operated stirrer until equilibrium was attained. A slightly different procedure was adopted in the case of mixtures containing large proportions of the acid. The quantities of the various components taken were such that their total volume was about 5 ml. This mixture was introduced into a Pyrex bulb of about 10-ml. capacity, which was then sealed and vigorously shaken in the thermostat by mechanical means. This procedure was necessitated by the high solubility of the acid and limitation in the quantities available. The solution and the residue were then separated in the usual way, and weighed separately. To the solution were added a few drops of dilute nitric acid and then dilute hydrochloric acid, drop by drop, until the precipitation of silver chloride was complete. The solution was diluted before precipitation whenever it was too concentrated with respect to periodic acid. This precaution is necessary to prevent part of the periodic acid from being lost by reaction with hydrochloric acid. The precipitate of silver chloride was allowed to settle overnight, filtered through a sintered-glass funnel crucible, washed first with water containing a few drops of nitric acid and finally with distilled water, dried at 105"C., and weighed. The filtrate was diluted to a suitable volume, and periodic acid was estimated in it by the following method: 25 ml. of the solution was pipetted into a 500-ml. bottle provided with a ground-in glass stopper which fitted tightly. The solution was diluted with about 150 ml. of water and acidified with sufficient 2 N sulfuric acid. Excess of solid potassium iodide was added and the bottle heated at 60°C. (water bath) for 15 min. The liberated iodine was titrated against standard sodium thiosulfate solution, using starch as indicator. 120,
+ 14KI + 7HzSOa = 7KzsO1f 7Hz0 4-812
SYSTEM SILVER OXIDE-PERIODIC ACID-WATER AT
35°C.
1113
The thiosulfate solution was standardized against pure recrystallized potassium iodate, and the strength of the solution was checked a t intervals during the course of the work. The same procedure was used for the estimation of silver and periodic acid in the residue. TABLE 1 The sustem silver ozide-periodic acidwater at 86°C. PEPCENTACES BY WEIGH1
Soh tions AgrO
1
1201
-.
Wet residues AgsO
-.
SOLID PEASE
XI01
Small Small Small
0.00 0.00
35.57 41.01
10.03 7.03
Small Small Small
0.00 0.04 0.05
31.22 23.23 27.12
9.73 7.40 8.63
Small Small Small
0.06 0.06 0.07
19.62 13.47 36.68
13.69 10.08 24.03
Small Small Small Small Small Small
0.18 1.22 3.30 15.33 26.41 34.50
16.36 36.66 29.08 35.91 35.93 30.41
13.16 29.10 32.72 37.18 39.31
Small Small Small
50.85 50.82 50.82
26.03 27.47 20.42
52.85 51.91 56.03
Small Small
56.56 61.01
13.06 15.35
58.50 60.95
Small Small
63.69 63.77
4.52 1.25
70.87 70.94
24.53
t
2AgsO
Isor.HsO
63.81
The results of the analyses of the various saturated solutions and their corresponding wet residues are given in table 1. The first column gives the amount of AgzO (which was in no case found to be greater than 0.04 per cent) and the second that of the acid, calculated as 1 2 0 7 , for the solution. The next two columns give these amounts for the wet residues. The acid has been expressed in
1114
P. P. GYANI
terms of 1 2 0 7 for two reasons: first, because of the uncertainty regarding the formula of periodic acid, it being not known definitely which hydrate of its hypothetical anhydride, 1201, is periodic acid. Second, if periodic acid is regarded as I~O7.5H20,which is the formula generally assigned to it, and if it is taken as one of the components in the three-component system under investigation, such reported salts as AgIO, and AgJ06, if they exist, cannot be accommodated within the triangular diagram. This difficulty has been overcome by taking 1 2 0 1 itself as one of the components instead of periodic acid.
FIG.I DISCUSSION
The results obtained are set down on a triangular diagram (figure 1). The composition of the solid phase was determined by Schreinemakers’ method of met residues (14). Owing to the very low solubility of the various solid phases the saturation curves are so near the H20-1207edge of the diagram that they appear to coincide with it. If the figure is drawn out of proportion so as to make these curves distinguishable, the qualitative diagram of figure 2 is obtained. The point A on this diagram represents the binary saturation point of silver oxide, and A B is its ternary saturation curve. This curve is extremely small and has not been experimentally realized. BC is the saturation curve of the anhydrous salt 5Ag20.1& represented by the point G on the base of the tri-
SYSTEM SILVER OXIDE-PERIODIC
ACID-WATER
AT
35°C.
1115
angle. The points B and C correspond to solutions in which concentrations of periodic acid are 0.00 per cent and 0.065 per cent 1207,respectively. The compound (iAg20.1207 can therefore exist in contact with solutions whose concentrations with respect to periodic acid lie within these limits. The tie-lines corresponding to the curve CD do not meet at the base of the triangle but at a point H within it, corresponding to the composition 2Ag20.1207.H20 for the solid phase. This compound can exist in contact with solutions which contain between 0.065 and 50.83 per cent 1.~0~. In contact with solutions more concentrated with respect to the acid, that is, from 50.83 to 63.80 per cent 1 2 0 7 , represented by points on the curve DE, the solid phase that exists is Ag20.1207,
FIQ.2 represented by the point K on the base of the triangle. F is the binary saturation point of periodic acid. EF represents its ternary saturation curve which, being extremely small, has not been experimentally realized. The point M represents the composition of d i d periodic acid, supposing it to be HI04.2H20in contact with aqueous soli i o n . The compoun . 5Ag~0.1~07 is a deep black crystalline powder. The compound 2 A g ~ .Iz 0 )7* Hz0 forms well-defined chocolate-brown crystals. When powdered it a p p e a deep red. The compound AgzO-Iz0.1separates in the form of deep yellow crystals. It will be observed from figwe 2 that the straight line joining the point repre-
1116
P. P. GYANI
SAMPLE
I............................ 1 1 , .. . . . . . . . . . . . . . . . . . . . . . . . . 111... . . . . . . . . . . . . . . . . . . . . . . . .
AgzO
I&
per c e l l
per cesf
75. a4 75.91 76.05
23.78 23.73 23.69
Required for 5Ag,O.I~07:76.0 per cent AgzO; 24.0 per cent I z 0 7 .
required for the compound 5Ag20.LOr. In fact, this method of progressive washing was found to be the most satisfactory for obtaining the latter compound in the pure state. Rise of temperature favors the transformation. Boiling, for example, brings about the change in a few minutes. Therefore, the compound 2Ag20.1207.H20 can exist in contact with aqueous solutions in which the ratio of 120.1 to Ag2O is greater than that which corresponds to the formula of the compound; that is, it can exist in contact with solutions containing free periodic acid whose concentration may be as low as 0.065 per cent 1 2 0 7 (cf. table 1).The compound 2Ag20. 1207.H20, crystallized from more concentrated solutions of periodic acid, was washed with a solution of the particular strength mentioned above. This solution in turn was obtained by washing some of the compound 2Ag20.1207.HZO practically free from periodic acid and stirring it with water until equilibrium was obtained. The amount of free acid adhering to the sample after washing with water thus prepared would be negligibly small. The residue was then dried over calcium chloride and analyzed. The results are given in table 3. The straight line joining the point representing the compound Ag20.1207 to
SYSTEM SILVER OXIDE-PERIODIC
AFID-WATER
AT
35°C.
1117
the water vertex does not intersect the saturation curve for this compound but lies wholly on the acid side of it. This compound can, therefore, coexist with solutions containing excess of periodic acid (50.83-63.80 per cent of 1201; cf. table 1). It decomposed on washing with water and therefore could not be isolated in a pure state. This compound alone can coexist with a solution saturated with periodic acid. The compound 5AgZ0.Iz0,, as is evident from its formula, does not possess any hydrogen atom in the molecule. It must therefore be an anhydrous normal salt of periodic acid and its empirical formula must be AgJOs. To confirm this conclusion an attempt was made to measure the vapor pressure of the compound. The manometer used for this purpose was similar to that used by B. P. Gyani (6). Measurements were made at 90°C. No definite vapor pressure was recorded. The pressure continued to increase slowly with time a t the rate of about 1 mm. of oil per hour. The vapor pressure was only about 4 mm. of oil, equivalent to 0.26 mm. of mercury, 1 hour after attainment of the desired temperature. The reaction involved was irreversible with respect to temperature. Frequent evacuation of the bulb did not result in any abrupt fall in pressure, TABLE 3 Analysis of the sa2t believed to be 2Ag20.1~07.HtO
I .............................
11, . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.. . . . . . . . . . . . . . . . . . . . . . . . . . . .
$67 C W I
p n cent
54.42 54.58 54.47
42.81 42.69 42.89
0 Time, h r . . ................. Temperature, "C... . . . . . . . . Room temperature Pressure, mm. Hg. ......... 0.0
f
2
3
0.2
1.6
0 Time, hr.. ........................ Temperature, "C.. . . . . . . . . . . . . . . . . Room temperature 0.0 Pressure, mm. Hg. ................
62 102 0.8
71
51 102
102
6.7
2.9
st 102 1.0
11.0
gt 102
1.0
gt
102 14.5
104 102 1.1
SYSTEM SILVER OXIDE-PERIODIC
ACID-WATER
hT
35°C.
1119
adsorbed water, which persists even when the samples are dried over phosphorus pent oxide. SUMMARY
The reaction of silver oxide with periodic acid in aqueous solution at 35°C. has been studied in the complete absence of nitric acid or alkali salts. It was' found that three definite salts of silver with increasing contents of silver oxide are formed as the ratio of this substance to the acid is increased: namely, 5 A g ~ 0 . 1 ~ 0 72Ag20 , .I~O,.HZO,and Ag,O ' 1 ~ 0 7 . Some properties of these salts have been noted and .the conditions for their stability in solution with respect to the concentration of the acid ascertained. The behavior of the first two under evacuation has been described. The authqr is grateful to Professor B. P. Gyani for constant help and guidance and to the Patna University for the award of a research scholarship. REFERENCES
(1) A M M E R M ~ L LF., E RAND , MAGNUS, G.: Pogg. Ann. 28, 514 (1833). (2) BAERTSCHI, P.: Helv. Phys. Acta 16, 218 (1943). (3) BOOTH,H.S.:Inorganic Syntheses, Vol. I, p. 168. McGraa-Hill Book Company, Inc., New York and London (1939). (4) CURTI,R . , A N D COGGIOLA, M.: Gam. chim. ital. 71, 487 (1941). L.: Char. chim. ital. 74, 43 (1944). (5) FERRARI,A.,CURTI,R., A N D CAVAWA, (6) GYANI,B. P.: J. Indian Chem. SOC.26, 307 (1949). (7) GYANI,P . P.: J. Indian Chem. SOC.27, 5 (1950). (8) KIMMINS, C. W.: J. Chem. SOC.61, 359 (1887). (9) MELLOR,J. W.:A Comprehensive Treatise on Inorganic and Theorelical Chemistry, Vol. 11, p. 406. Longmans, Green and Company, London (1923). (10) PARTINGTON, J. R.,A N D BAHI;,R. K . : J. Chem. SOC.1934, 1086. (11) RAMMELSBERG, C. F.: Ber. 2, 17 (1869). (12) ROSEXHEIM, A , , A N D LIEBKXECHT, 0.:Ann. 908, 55 (1899). (13) SAHNEY, R. C., AGGARWAL,S. L., A N D SINGH,S. M.: J. Indian Chem. SOC. 23, 177 (1946). (14) SCHREINEMAKERS, F. A. H.: Z. physih Chem. 11, 81 (1893). C. C.: J. Chem. Phys. 9, 379 (1941). (15) STEPHENSON, (16) STEPHENSON, C. C., AND ADAMS,H. E.: J. Am. Chem. SOC. 66,1412 (1944). (17) WELLS,H.L.: J. Am. Chem. SOC.26, 278 (1901).
