FREEZING-POIKT CURVE FOR WATER CONTAINING HYDROCHLORIC ACID A N D P H E N O L
BY J. A. EMERY AND F. K. CAMMEROK
I n the work here described, the mass of water was always relatively large as compared with the masses of hydrochloric acid and phenol. T h e amount of water and hydrochloric acid dissolved i n the phase liquid phenol was always sniall, and consequently the separation of solid phenol on cooling, affected the concentration of the hydrochloric acid in the water to an entirely negligible extent. A series of solutions was prepared from pure hydrochloric acid and distilled water, ranging in concentration from pure water to about a half normal ( 4 2 ) solution. T h e strength of this last solution was carefully determined gravimetrically, the chlorine being weighed as silver chlorid. T h e solution thus prepared was taken as the standard, and compared with each of the others by titration against a solution of sodium hydroxide. A series was made by each of us separately. T h e column marked ‘‘ E ” i n the table was calculated from determinations made by of alkali, with titrating against a weak solution about (./IO) phenolphthalein as indicator. T h e column “C ” was obtained by titrating against a relatively strong about ( 4 2 ) solution of alkali, using cochineal as indicator. T h e burettes were not calibrated, but ’the determinations, using widely varied amounts of solution and from different parts of the instruments, compared very well with one another. T h e freezing-points were determined with the Beckmann apparatus, using differential thermometers made by Goetze.
Fveezing-poizt Curve fov Watev
131
Here again a separate series was made by each of 11s with different instruments. For the determinations in column E, the thermometer used was a very fine one with large bulb and capillary. It ( ( s e t " very readily, I n the other series C, the thermometer had a short stout bulb with very fine capillary. Both instruments were graduated to hundredths of a degree (0.01'C) and thousandths were readily estimated with a glass, using all due precautions in making the readings. T h e determinations compared well together, the variations being about equally distributed as to sign, so it was not deemed worth while to calibrate the instruments. T h e phenol was purified by distillation, first and last portions being discarded. It was carefully kept in a flask with a closely fitting stopper carrying a calcium chlorid drying tube. When needed it was melted over a Bunsen flame, the desired amount withdrawn by a pipette and quickly transferred to the solution under examination. About 1.5 cc of liquid phenol to 2 0 cc of the hydrochloric acid solution was the proportion generally used. T h e freezing-points were determined as follows : T h e solution prepared as just described was introduced into the instrument and cooled in the usual manner with occasional stirring. T h e mercury would fall regularly. After more or less undercooling had taken place, the separated phenol would rather suddenly solidify, which would be accotnpanied by rapid rising of the mercury i n the thermometer. T h e rise would be but momentary, and the mercury would commence to fall again about as rapidly, but apparently more regularly than before the separation of the solid phenol. T h e undercooling, separation of ice and rise of the mercury to the freezing-point would proceed as usual. For the first determination in each case, the amount of supercooling was generally large (2'--4') and the reading somewhat low, but much less than previous experience with the method would have led us to expect. T h e tube containing the solution mould be withdrawn from the freezing bath, warmed until the temperature
132
J. A.Emery ana? E;: K. Camevon
had risen 2'-3', being thoroughly shaken meanwhile ; and again placed i n the bath of freezing mixture. T h e subsequent readings were generally made with but little (about 0.5' on the average) previous undercooling. T h e readings compared very well with one another. When a sufficient number of satisfactory readings had been obtained, the apparatus was carefully cleaned, distilled water introduced, and its freezing-point determined. T h e difference between the freezing-points of the solution and pure water was the reading recorded. T h i s method was followed in every case. T h e barometric readings were taken from time to time during the determinations. In every case recorded here, the variation i n this respect was quite small and could have had no appreciable effect on the determination. Every effort was made to prevent prejudiced readings. T h e freezing-point determinations were all completed before the concentrations of the solutions were known, and all the experimental data were obtained before any attempt mas made to tabulate or chart them. I t seems proper to say that we regard the amount of hydrochloric acid given under C as the more reliable, while the freezingpoints under E are to be given the preference. I n Table I the
E
I
0.0000
0 0000
0.0000
0.0000
11
0.8832 I . 6040 2.5437 4.4798 8.6349 I 8.2478
0.8668 I ,6295 2.5565
0.0242 1 0,0233 0.0440 0.0447 0.0698 0.0701 0.1229 1 0.1242 0.2369 0.248 I 0.5006 0.5006
1'
9.0436 18.2478
1
I
-1.17g0 -1.I77O -1.267 1 -1.268 -1.340 -1.334 -1.436 --I.424 -1.636 -1.710' -2.077 -2.077 -3.007 -3.010
first pair of columns record the grams hydrochloric acid per liter of solution. T h e second the number of reacting weights per liter of solution. T h e third the corresponding freezingpoints on the centigrade scale. We have in our possession some data for more concentrated solutions than those tabulated Unfortunately, through the breaking of the mercury column, a direct coniparison with the freezing-point of water was not possible in this case alone.
FYeezing-$oint Cur-def o y W'aier
I33
above. All our results when charted fall on or very close to a straight line. But the data for these more concentrated solutions are not given here, as we regard them as very unsatisfactory. T h e determinations made by each of us separately vary nearly 5 percent in some cases, nor do the individual readings compare more favorably with one another. As an example, for a solution containing 26.7695 gms of hydrochloric acid per liter, one of us found the freezing-point to be - 3.788' ; the other found it to be - 3.973' ; the average of these would be - 3.880') the computed value being 3.855'. While the variation in our observations is about 4.6 percent, the error in the average is less than I percent, corresponding to less than 0.25 gms hydrochloric acid per liter of solution. Starting from the same initial temperature and with the same amount of undercooling, fairly concordant results would be obtained. But slight variations in either of these particulars would cause wide variations in the readings. T h a t the instruments were not at fault was shown by the excellent results in obtaining the freezing-point of water at the same time. T h e work was unfortunately interrupted before this difficulty could be thoroughly investigated. T h e comparison of our results with those obtained for hydrogen chlorid and water alone is interesting. I n Table I1 the
TABLEI1 0.0238
0.088O
0.0447
0.161
0.0701
0.2j7
0 . I 242
I
0.457
0.248 I 0.5006
0.898 1.828 ~
I
3,672' 3.601 3.666 3.679 3.619 3.6j1 --3.648
average
first column represents reacting weights per liter ; the second the corresponding depression of the freezing-point found ; the third the lowering of the freezing-point per reacting weight of hydrogen chlorid in a liter of solution. In Table I11 similar
I34
Freezing-poiizt Cuvve for Water TABLEI11 0.0136 0.0409 0.0546 0.0838 0.0982
I
I
00.5O 0.15 0.20
~
0.30 0.35
~
I I
I I
1
3.676' 3.667 3.663 3.579 3.564
-_
3.630 average
data are presented calculated from the results of Jones for hydrochloric acid and water. It will be noticed that the depression of the freezing-point for a reacting weight of hydrochloric acid per liter of solution is a constant. And i n both cases the constants agree with one another well within the possible errors of experiment. It follows that the curve in each case is a straight line, and the curves are parallel. T h i s simply means that within the temperature range involved the solubility of phenol in water is practically constant, and the consequent lowering of the freezing-point is a purely additive effect. T o sum u p : I. T h e freezing-point of water, saturated with respect to phenolis -1.179' C. 11. T h e freezing-point curve for solutions of hydrogen chlorid in water is a straight line. T h e freezing-point curve for aqueous solutions of hydrogen chlorid saturated with respect to phenol is a straight line, and 111. T h e curves just mentioned are parallel, i. e. the depression of the freezing-point of water by hydrogen chlorid and phenol, under the conditions described, is an additive effect. Biochenzic La bora tory, U. S. DepartnsenZ of Agriczdture, Washiizgton, U . C.
