THE SOLUBILITIES OF CALCIUM HYDR,OXIDE, CALCIUM IODATE, AND AMMONIUM PERCHLORATE I N DILUTE AMMONIACAL SOLUTIONS I. M. KOLTHOFF
AND
V. A. STENGER
School of Chemistry, University of Minnesota, Minneapolis, Minnesota Received J u l y 24, 1935
In a previous paper (6) it has been mentioned that the effect of ammonia upon the adsorption of calcium hydroxide from aqueous medium by silica gel and hydrous oxides is not to be attributed to a complex formation between calcium hydroxide or calcium ions and ammonia. More definite proof of this statement was obtained from solubility measurements of calcium hydroxide in solutions having a concentration up to 2 N in ammonia. Since ammonia appeared to have a marked lowering affect upon the solubility of calcium hydroxide, it was decided to determine the solubilities of calcium iodate and of ammonium perchlorate in the same media. MATERIALS USED
Calcium oxide. A hot solution of C.P. calcium chloride was treated with a slight excess of a solution of ammonium oxalate. The precipitate was digested, filtered, washed until free from chloride, dried and ignited in an electric furnace. Calcium iodate, C a ( 1 0 ~ ) ~ . 6 H ~ O A . hot solution of C.P. calcium chloride was treated with a slight excess of potassium iodate. The precipitate, after washing, was twice recrystallized from conductivity water. Upon drying a t 110°C. the monohydrate is formed. On shaking with water or dilute ammonia solution jt is quickly transformed into the hexahydrate. Ammonium perchlorate. A Kahlbaum product recrystallized from water was used. Ammonia. A solution of carbonate-free ammonia was obtained by distillation of 20 per cent ammonia in the presence of an excess of barium hydroxide. The distillate was kept in a paraffined container and protected from carbon dioxide of the air. SOLUBILITY DETERMINATION
Solubilities were determined in a thermostat a t 25.OOOC. f 0.02"C. Paraffined containers were used throughout this work, although with glassstoppered Pyrex bottles the same results were found. In all cases equilibrium was attained after fourteen to twenty hours of shaking. The pre639
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I. M. KOLTIIOFF AND V. A. STENGER
cipitates were then allowed to settle in the thermostat and samples of the supernatant liquids analyzed. TABLE 1 Solubility of calcium oxide in ammoniacal solutions at W C . CONCENTRATIOS OF NHa
DENBITY OF BATURATED BOLUTION AT 25'c.
I
CONCENTRATION OF CALCIUX H Y D R O X I D E
filoles per liter
N
0 0.496 0.981 1,475 1.955
0.998 0.994 0.989 0.985 0.982
0.02128 0.01993 0.01850 0.01700 0.01571
'0
per '00 '0. of solution
CaO par 100 ~olution
grams
grams
0.1194 0.1117 0.1038 0.0953 0.0881
0.1196 0.1124 0.1049 0.0967 0.0896
TABLE 2 Solubility o j calcium iodate hexahudrate in ammoniacal solutions at 86°C. CONCENTRATION OF NH3
CONCENTRATION OF
Moles per liter
Ca(I03)z pef 100 cc. of solution grams
grams
0,999 0.995 0.991 0.987 0.983
0,00785 0.00779 0.00756 0.00733 0.00715
0.306 0,304 0.295 0.285 0.279
0.306 0.305 0.298 0.289 0.284
N
0 0.489 0.986 1.422 1.966
Ca(I0s)z
DENSITY OF SATURATED 6OLUTION AT 25'C.
Ca(IOd2 per 100 g. of solution
TABLE 3 Solubility of ammonium perchlorate in ammoniacal solutions at 25°C. CONCENTRATION OF
lcoleB per liter
NHiClOi per 100 cc. of solution
NHiClOa per 100 g. of solution
grams
grams
1.830 1.841 1.871 1.915 1.954 2.049
21,50 21,63 21.98 22.50 22.96 24.08
19.64 19.81 20.16 20.68 21.14 22.23
N
0 0.443 0.876 1.303 1,731 2.59
1.095 1.092 1.089 1.088
1.086 1.084
NHaC104
ANALYSES
In the so1ubilit)ydeterminations of calcium hydroxide the calcium and hydroxide content was determined. After removing the excess ammonia,
SOLUBILITIES I N DILUTE AMMONIACAL SOLUTIONS
64 1
the calcium was precipitated from weakly acid solution as oxalate, and titrated according to standard procedures with potassium permanganate. Other samples were evaporated to dryness, the residues treated with an excess of standard hydrochloric acid, carbon dioxide driven off by boiling, and the acid back-titrated with sodium hydroxide, using methyl red as indicator. The results obtained in both procedures agreed within 0.5 per cent, the oxidimetric method always yielding higher values than the acidimetric one. The solubility of calcium iodate was found from iodometric titrations of the iodate. The ammonium perchlorate content of the solutions was determined by evaporating known volumes to dryness and weighing after drying to constant weight a t 110°C. All analyses have been made in duplicate or triplicate. Duplicate analyses with samples from the same bottle agreed within 0.1 per cent in the case of ammonium perchlorate; with samples from different bottles discrepancies of the order of 1per cent were sometimes noticed. Therefore the solubility da$a given for ammonium perchlorate do not seem to be as exact as those of the other two substances. The highest values obtained are reported in table 3. In all cases the densities of the superndtant liquids were determined a t 25°C. Correspondingly the solubilities found are expressed in moles per liter and in grams per 100 g. and per 100 cc. of solution. RESULTS
The results are given in tables 1,2, and 3. DISCUSSION O F THE RESULTS
1. Solubilities in water. Data reported in the literature on the solubility of calcium oxide in water vary from 0.115 to 0.125 g. of CaO per 100 cc. a t 25OC. (cf. Seidell, 1928). I n a recent paper Johnston and Grove (5) gave results obtained with crystalline calcium hydroxide, which are 7.5 per cent lower than the figure obtained with our product. The difference is probably due to the difference in the nature of the saturating phases used. The values obtained with our product of calcium oxide were quite reproducible and independent of the amount of solid taken. The solubility of calcium iodate hexahydrate agrees exactly with the figure determined by Hill and Brown (3). Their paper was published after this work had been finished. There is a wide divergency in the literature on the solubility of ammonium perchlorate in w3ter; expressed in grams of NHIC104 per 1OOg. of solution the following data a t 25°C. are reported 21.1 (Carlson (l), by interpolation) ; 19.8 (Mazzuchelli and Rosa (8) by interpolation), 20.02 (Freeth (2), a t 25OC.); 19.95 (Willard and Smith (lo), at 25°C.). The figure of 19.64 determined in this study is lower than any of the pre-
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I. M. KOLTHOFF AND V. A. STENGER
vious values reported, but was found to be consistent with various times of shaking and different amounts of solid body. 2. The effect of ammonia upon the solubilities of the three substances investigated is quite different. The solubility of ammonium perchlorate increases regularly with increasing ammonia concentration in the solution, that of calcium iodate hexahydrate decreases slightly, and that of calcium hydroxide very markedly. Konowalow (7) at 20°C. found 0.1017 g. of calcium oxide per 100 cc. of water, and 0.0610 g. per 100 cc. of solution containing 5.2 per cent of ammonia (about 3 N ) . From the results given in table 1 it may be concluded that up to a concentration of 2 N in ammonia the solubility of calcium oxide decreases linearly. S = 0.1194
,
- 0.016 C N H ~
S is solubility expressed in grams of CaO per 100 cc. of solution a t 25°C.; C N H s is the normality of ammonia. The decrease of the solubility of calcium hydroxide in the presence of ammonia cannot be attributed to a common ion effect. For example, in a solution 1 N with respect to ammonia and saturated with lime, the concentration of the hydroxyl ions contributed by the ammonia is only 1.3 per cent of that formed by dissociation of the calcium hydroxide. The decrease of the solubility of calcium hydroxide in the presence of ammonia therefore has to be attributed to a specific medium effect. Ammonia a t 24.5OC. has a dielectric constant (4) of 14.9 and is therefore expected to decrease markedly the dielectric constant of aqueous solutions, and consequently the dissociation of electrolytes. It should be remembered that the second dissociation of calcium hydroxide is far from being complete; in the presence of ammonia it is still further decreased and consequently the solubility also. Qualitatively speaking, ammonia has here the same effect as organic solvents, such as methanol, ethanol, etc., have on the dielectric constant of aqueous solutions. It is beyond the scope of this paper to investigate in further detail the striking effect of ammonia upon the solubility of calcium oxide. 3. The results obtained confirm the primary object of this investigation, namely, to prove that the effect of ammonia on the adsorption of calcium hydroxide by hydrous oxides and silica gel is not to be attributed to a complex formation. The linear decrease of the solubility with the ammonia concentration and the constant composition of the solid show definitely that up to concentrations of 2 N in ammonia no complexes are formed in the solution.
SOLUBILITIES IN DILUTE AMMONIACAL SOLUTIONS
643
SUMMARY
1. The solubilities of calcium hydroxide, calcium iodate, and ammonium perchlorate a t 25OC. in water and in solutions containing concentrations of ammonia up to 2 N have been determined. 2. The solubility S (in grams of CaO per 100 cc. of solution a t 25°C.) of calcium hydroxide decreases linearly with increasing ammonia concentration : S = 0.1194
- 0.016 C N H ~
3. No complex compounds between calcium hydroxide or calcium ions and ammonia are formed in the solution at ammonia concentrations smaller than 2 AT. REFERENCES (1) CARLSON, B.: Klason's Tidskrift, p. 247 (lglo), from Tables Annuelles 1, 379 (1910). (2) FREETH, F. A,: Rec. trav. chim. 43, 475 (1924). (3) HILL, A. E., AND BROWN, S. F.: J. Am. Chem. SOC.63,4316 (1931). (4) International Critical Tables, Vol. VI, p. 76. McGraw-Hill Book Co., New York (1929). ( 5 ) JOHNSTON, J., ARD GROVE,C. : J. Am. Chem. Soc. 63, 3976 (1931). (6) KOLTHOFF, I. M., AND STENGER, V. A , : J. Phys. Chem. 36, 2113 (1932). (7) KONOWALOW, D.: J. Russ. Phys:. Chem. Soc. 31, 985 (1899). (8) MAZZUCHELLI, A., AND ROSA,A,: Atti accad. Lincei [5130, 11,270 (1921). (9) SEIDELL, A.: Solubilities of Inorganic and Organic Compounds, Vol. I (1919), Vol. I1 (1928). D. Van Nostrand Co., New York. (10) WILLARD, H. H., AND SMITH,G. F.: J. Am. Chem. Soc. 46,286 (1923).
