The Solubilities and Densities of Saturated Solutions of Sodium and

T H E SOLUBILITIES AXD D E S S I T I E S O F SATURATED SOLUTIONS OF SODIUM AKD POTASSILhl HALIDES AT 25'

Downloaded by UNIV OF ARIZONA on September 4, 2015 | http://pubs.acs.org Publication Date: January 1, 1926 | doi: 10.1021/j150273a012

BY ARTHUR F. SCOTT A S D W. RONALD FRAZIER

In order to compute "The Changes in Volume upon Solution in Water of the Halogen Salts of the Alkali 1Ietals." Professor G . P. Baster' and his students have made an elaborate series of measurements of the densities of these solutions over a wide range of concentrations for t'emperatures between oo and 100'. Only in a few cases. however, were measurements made with saturated solutions. It was the original intention of the present investigation t o fill in this gap and further, to make a syst'ematic series of solubility determinations over the same range of temperature. This work, unfortunately, has been interrupted and its completion must be postponed indefinitely; consequently, it seems desirable to publish the results which have been obtained up to t,he present time.

Purification of Materials Throughout the present investigation the earlier work n-as taken as a model and every effort was made to att'ain the same degree of precision in order that the t i y o sets of data would be on a comparable basis. Accordingly the preparation and purification of the materials used followed as nearly as possible the methods described in the second of the papers already cited. The few cases \There this duplication was not possible, are noted below: Sodj2uvz brorrzitle and sodium iodide were obt'ained by treating recrystallized Podium carbonate with purified hydrobroiiiic and hydriodic acids respectively. The products thus obtained were then crystallized t'wicc in a quartz dish, and in both cases the salts were dried in a n electrically heat,ed porcelain furnace a t 300' for four hours. S i l w nitrate was purified by making a saturated solution of analytically pure material which was then precipitated by the addition of an equal volume of redistilled nitric acid. The crystals were separated from the mot,her liquor by means of centrifuging. When dry, they were brought just, to the fusion point. The solutions of this salt which were employed in the solubility determinations, were prepared immediately before they were used. Apparatus The Thermostat .-The solutions used in the density and solubility measurements were brought to the saturation state in a constant temperature bath. The temperature of the bath was controlled by a large, four-finger mercury-toluene regulator and was readily kept constant to within 0.01'. When in operation, the bath was maintained a t 2 j o ,the temperature being determined by a fifty-degree thermometer calibrated by the Bureau of Stand-

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Baxter, Roylston, Mueller, Black, and Goode: J. Am. Chem. SOC., 1 3 , 901 (1911); Baxter and FVallace: 38, 70 (1916).


460

ARTHCR F. SCOTT AND W. ROSALD FRAZIER

ards. This thermometer was graduated in tenths of a degree and could be read to hundredths. In the thermostat was also a contrivance for rotating the flasks containing the solutions t o be saturated. This part of the apparatus mas completely immersed in the bath. The Flasks.-Density measurements were made by means of two ordinary 25 cc. graduated flasks, the necks of which had been constricted to secure greater accuracy in setting the meniscus. The interior diameter of the constricted portion of the neck was 2-3 mm. The volumes of the twoflaskswere To accomplish this the determined by finding their mater content a t 25'. flask was allowed to remain in the constant temperature bath until the meniscus attained a const'ant position, which operation usually required two t o three hours. Finally the meniscus was adjusted and the neck of the flask was dried by touching it with a piece of filter paper. The flask was always weighed with a similarly treated counterpoise and both were allowed to stand in the balance case one hour before weighing. From the apparent weights of water the volumes were calculated by multiplying by the factor, 1.004001, the density of water a t z j o being assumed to be 0.997071. These figures are taken directly from t'he paper by Baster and Wallace. The flasks were calibrated a t the beginning and a t the end of the work which lasted over a period of three months. The apparent weights of the mater in both cases showed a change of only 0.1mg.; hence the volumes may be assumed to have remained const,ant. Procedure The solution to be saturated r a s contained in a 2 5 0 cc. bottle, the ground glass stopper of which was carefully fitted. Usually about 80 cc. of solution was made so that there would be present approximately j gm. of the solid salt a t saturation. Particular care was taken in sealing the flask. The neck of the bottle was always completely dried before the stopper was inserted. Then the stopper was coated with paraffin and finally wired t o the neck of the flask. I t was found that this precaution prevented contamination from the bath and also kept the mouth of the bottle dry for subsequent operations. The bottle containing the solution was next placed in the rotating device in the thermostat and shaken for one hour, after which it was allowed t o stand in the bath for one hour. With the exception of the iodides these two operations were repeated several times before the solution mas used, although t'ests demonstrated that this repetition was superfluous. Several methods of t,ransferring the saturated solution t o the density flask were tried and the following, which was the one finally adopted, was undoubtedly just as accurate as the others and had the advantage of being the simplest, When the solution was ready to be transferred, the bottle was held in the bath so that only the neck protruded. The glass stopper was carefully removed and replaced by a two-hole rubber stopper. I n one hole of t'he stopper was one arm of a small, inverted glass U-tube, the bend coming just above the stopper. The arm of the tube in the saturation bottle extended almost t o the bottom; its end was sealed off and a small hole was blown in the side of the tube about I cm. from the end. This was done in order t o prevent


SOLUBILITIES A S D DENSITIES OF SATURATED SOLUTIONS

46 I

any crystals on the bottom of the bottle from being carried over into the density flask, The other end was drawn int,o a fine capillary which fitted into the constricted neck of the density flask. The second hole cf the rubber stopper was provided with a small piece of glass tubing through which a slight pressure could be exerted, thereby forcing the saturat'ed solution over into the density flask. Of course the density flask and also the transferring tube were kept in the constant temperature bath previous to use. Xfter the transference of the saturated solution in the above manner, the density flask was allowed to remain in the bath for about half an hour. Then the flask along with some of the water was removed from the termostat in a Dewar beaker. This Dewar beaker was transparent and slightly larger than t,he density flasks. With the flask thus in the beaker it was a comparatively easy matter to set the meniscus by means of small capillary tubes, an operation which required usually about a minute. Following the preliminary adjustment of the meniscus the density flask was again set in the thermostat for fifteen minutes and the meniscus was checked in the same way. When the adjustment, had been found satisfactory, the neck of the flask above the constriction was wiped with a small piece of filter paper. Measurements made with a Beckmann thermometer showed that the temperature of the water in the Dewar beaker changed only 0 . 0 0 6 ~in three minutes! a variation which was less than that of the bath itself. To correct t,he weight of solution t o vacuum, it would have been necessary t o know the exact volume a t the temperature of weighing. Since this )vas not easy t o ascertain, it was assumed that the volume was the same as a t 2 j". This assumption would not introduce any great error because the temperature at the time of weighing TWS riever far from that of the bath. In all cases. therefore, the weights of solutions were correckd to vacuum by the usual formula involving terms for barometric and vapor pressures. That the above procedure for obtaining a saturated solution and then its density is rather satisfactory, can be seen in t,he results of solutions of sodium chloride. In t'his case four different solutions prepared on four different days eshibited an extreme difference in density values of only one part in fifteen thousand. 1-sually only one solution was prepared. After portions had heen transferred to the two density flasks, two samples (approsimately 5 cc.) w r e transferred to each of two tared weighing bottles. A second weighing gave, of course, the weight of the sample. These samples were nest, transferred carefully to one liter, glass-stoppered Erlenmeyer flasks, and diluted t o about 500 CC. From the weight, of the solution the weight of silver nitrate necessary to precipitate the halogen content was computed. This quantity plus an excess of about 0.5 gin. was dissolved in I j o cc. water. Then, after the salt solution had been made acid by the addition of I cc. of concentrated nitric acid, the silver solution was added slowly xith constant stirring. The mixture was shaken and the precipitate permitted to sett,le over night. The precipitates obtained in this manner were next washed in order to eliminate the alkali nitrat'e present,. In the case of the bromide and iodide precipitates the

462

ARTHVR F. SCOTT A S D W. ROSALD FRAZIER


washing was done by decantation, five times with pure water; in the case of the more soluble chloride precipitate, however, the washing was also by decantation, but first with a one percent silver nitrate solution and finally once with pure water. Following the washing the precipitates were transferred to Gooch crucibles and heated in an oven at 120' to constant weight.

Results The data obtained in the present series of measurements are tabulated in Table I. TABLE I Density and Solubility Data Salt

JTeight of Volume of solution solution in vacuum

Density

Vacuum weight of sample

Vacuum Keight of Crams salt weight salt in in ~ o o of AgX samp!e grams watrr

XaC1 30.4406 zj.4Ioj I . 19795 7,9637 j.156j 29.4303 24.5669 1.19797 8.2454 5.338; 30.4395 2j.qIOj 1.19791 30.4416 2 5 . 4 1 0 5 1.19799 Average.. . . . . . . . . I . 19796 XaBr 39.1782 25.4105 1,54181 6.9726 6.1866 37.8775 24.j669 1.54181 i . 2 1 9 7 6.4014 ~ ~ v e r a .g.e. . . . . . . . . 1 . 54181 S a 1 48.7637 ~ j . 4 1 0 51.91904 9.9725 10.1189 47.1434 24.j669 1.91898 11,180711.3422 Average. , , . . . . . I . 91901 Kc1 29.9301 2 5 . 4 1 0 5 1.17786 ;.io42 3 , 9 0 7 0 28.9362 2 4 . 5 6 6 9 1.17785 6.4205) 3,2547 7.5590 3.8351 .~ erage ~. ... . . . . . . . .1.1;;86 KBr 35.0jo5 2j.4105 1.3j937 6.5506 4,1930 33,8865 24.j669 1,37936 6 . 4 j 4 6 1.1327 Average . . . . . . . . . . .1.37937 KI 4 3 , 7 3 3 4 ~ j . 4 1 0 51 . j 2 1 0 j j.9590 6.7227 j.0ij7 42.2831 24.5669 1.j2114 8 . 3 7 2 0 8.4651 7.1.;j 7 dverage . . . . . . . . . . .1 . 7 2 1 1 1 ,

,

2.1029 26.406 2.1778 26.405

3.3901 3.5080

26.406 48.622 48.590 48.61

6.4610 64.787 7.2420 64.730 64.76 2.0322 26,375 1.6929 26.36.i 1.9948 26.389 26.38 2,6572 40.~6j 2.6190 4 0 . 5 7 7 40.57 4.7533

jg.j23

j.0030

59.760 j g . 765

5.0595

59.j.:

It should be noted that the data for the iodides are less certain than those for the other salts. This is due to the fact that the saturated solutions appeared t o liberat,e iodine on standing. For this reason the solutions were used as soon as possible after preparation. I t is of interest to compare the results presented in this paperwith those given in the literature. Apparently the only density values availalile are those determined by Berkeley.' His figures for 2 jo,obtained by interpolation, are given below: 1

Berkeley: Phil. Trans., 203 A, 189 (1904).

SOLUBILITIES AND DENSITIES O F SATURATED SOLUTIOSS


NaCl Kcl

Berkeley 1.1978 1.1779

463

S and F I . 19796 I . 17786

In the paper of Baxter and Wallace curves are given which show the variation of the contraction in volume per gram of salt with a change of concentration. If the contraction for a saturation solution is computed in the same way, their representative points, when plotted on the above graph, fall precisely on estensions of the proper curves. Such a figure is not presented here because of the incomplete nature of this paper.

Summary The present communication gives values for the densities and solubilities of saturated solutions of the chlorides, bromides, and iodides of sodium and potassium a t 2 5 ' . A11 of the measurements recorded in this paper were made a t Reed College while most of the material was prepared a t Harvard University. The authors wish to acknowledge the kindness of Professor Baxter in permitting one of us t o work in his laboratory during the summer of 1924. A grant from the duPont Fund at that time helped t o defray part of the expense of the materials. The Rzce Institictc.

The Solubilities and Densities of Saturated Solutions of Sodium and

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