NOTES
316
titrated with standard hydrochloric acid, using equal parts of brom cresol green and methyl red as an indicator. ACETATE BUFFER, Bromine was determined by the familiar Volhard method.
TABLE I1 CHARACTERISTICS O F CIIROMlC SALTS I N pH 4.8, fi = 0.2 Compound
Cr(H20h CIS 0.0015M
Time, nun.
(1st wave)
18 37 107 3630 22 GO
2.9fiA 1.9 1.0 0.4 1.7 1.25
id
Vol. 63
-
TABLP I THESYSTEMMgBr2-NHaBr-H20
E112 -Eva (1st wave), (2nd wave),
v.
-0.84 .84 - .84
-
V.
-1.43
- .o - .87 - .87
Cr(H20)4C12 CI -1.45 -1.45 0.0009 Af Chromium 20 0.2 .9 acetate" Chromium 0.2 .9 nee tateb a This was the salt prepared as described in this paper. Its concentration was 0.37% (w./v.); assuming the formula for the non-electrolyte, this is approximately 0.00048 .If. May and Baker's "Chromium acetate," the concentration was0.27% (w./v.).
-
of Cr(I1) with ethylenediamine has a magnetic moment of 4.44.5 Bohr magnetons, corresponding t o four unpaired electrons. This means that a change of configuration similar to that postulated for cobalt would attend the reduction of a chromium complex. The standard reduction potential for Cr(NH&++++Cr(NH&++ is not known, but it has been estimatedl9 that it liesat about - 0 . 7 ~ .(ie., at about -0.95 v. with respect to the SCE). The hexaquochromium(II1) ion has a standard reduction potential of -0.414 v. (-0.66 v. us. SCE). Our observations, however, indicate that the hexaquochromium ion has approximately the same reduction potential as the hexammine under the conditiolis of our experiments, uiz., -0.84 v. us. the SCE at a concentration of about 111.
%
S O l Lition
MgBrz
%
NHiBr
50.31" 50.28"
0 0.14"
42.22 37.40 36.44"
3.75 8.13 9.20"
Wet solid
%
R'lgBra
%
Solid phase in Egiiilibriiiin
iVHdBr
43.60 12.00 44.50 20.15
14.95 20.36 38.73 28.37 28.25 5.67 72.45 13.91 37.80 2.05 69.20 5.65 0 44.OS" a Mean of several determinations.
MgBr2.6EI20 MgBrZ~6H20-MgBr2. NH4Br.6H*0 MgBr2.NHcBr,6Hz0 MgBrt.NH4Br.6H~0 MgBrt.NH4Br.6HtOh'H4Br NHaBr NH4Br NHaBr NI14Br
Results and Discussion The results obtained from this study are prcsented in Table I and Fig. 1 where all percentages HzO
A
(18) D. N. Hume and H. W. Stone, J . Am. Chem. SOC.,6 3 , 1200 (1941). (19) R. N. Keller and R. W. Parry in "The Chemiatry of t h e Coordination Compounds," ed. J. C. Bailar, Jr., Reinhold Publ. Corp., New York. N. Y., 1856,p. 186.
THE SYSTEM MAGNESIUM BROMIDE, iiMMONIUM BROMIDE AKD WATER ST 25'' BY
JACK ALLEN
CAMPBELL AND FREDERICK L. MARSH
Contribution from the Department of Chemisiry. Blackburn College, Carlinville, Illinois Received August 18, 1968
A compound, MgBr2.NH4Br.6Hp0,analogous to carnallite, was described by de Schulten12but there seems to have been no systematic phase study made of the three component system. Experimental The best commercially available grades of ammonium bromide and magnesium bromide hexahydrate were mixed in varying proportions with water and slowly rocked in a bath maintained at 25 f 0.02' until equilibrium was reached, usually for 48 hours. Both the liquid phases and wet solids were analyzed for ammonia and bromine. The former was determined by releasing the ammonia with caustic and distilling it into 4% boric acid where it was (1) Presented before the Ninth Annual Undergraduate Chemistry Symposium, Loyola University, Chicago, Illinois, May 17, 1958. (2) M. A. de Sohulten, Bull. SOC. chim., 17, 167 (1897).
MgBrz
NH4Br
Fig. 1.-Schreinemakers diagram of data exhibited in Table 1. Coexistent solid and liquid phases are joined by solid lines, while regions are delineated by dotted lines.
are on a weight basis. The solubility of magnesium bromide was found to be 50.31% which compares favorably with 50.68% reported by Getman.3 The solubility of 44.08y0 obtained for ammonium bromide may be compared with the value 43.8GyO obtained by Scott and D ~ r h a m . Coiifirming ~ the work of de Schulten2 the single double salt which was observed WRS found to have a composition conforming to MgBrz.NH4Br.6Hz0. The invariant solutions were found to have compositions of 50.28% MgBr2 and 0.14% n"4Br in equilibrium with compound and magnesium bromide hexahydrate, while compound and ammonium bromide were in equilibrium with a solution containing 36.44% MgBrl and 9.20% ammonium bromide. (3) I?. H. Cetman, R6c. irao. cham., 64,866 (1935). (4) A. F. Soott and E. J. Durham, Tam JOURNAL,34,535 (1930).
NOTES
Feb., 1959
317
The compound resembles carnallite in that it is an incongruently saturating type of double salt. Water decomposes it into ammonium bromide a i d a solution richer in mngnesium bromide.
THE EFFECT O F EXCESS SALT ON MINIMA OBSERVED I N ?/LOG C CURVES FOR SURFACE ACTIVE AGENTS BYS. P. HARROLD Basic Research Department, Thomas HedleU Le. Co. Ltd., A’ewcaslle upon Tune, 1 , England Rcceizmf Julu 25, 1955
The minimum which occurs in the surface tension (r)/concentration (C) curves of surface active agents has been variously explained as due to metal ions in the water71impurities in the chemical compounds examined2 or to time effect^.^ The most likely explanation is the presence of other components since it is to remove the minimum by successive purification processes, and to produce one by the addition of a third component.6 20 It has been observed that the addition of excess salt -3 -2 with a common ion removes the minimum in the log molarity. ?/log C curve for several anionic detergents. Fig. 1.-Surface tension of p-nonylbenxene sulfonate: I, d o n e in distilled water at 20”; 11, plus 0.5% bv weight Experimental Surface tensions Rere measured by the tlu S o u y tensiometer wit,h appropriate cor~ections.~Sodium alkylbenzene sulfonate (ABS) was prepared by direct sulfonation of tetmpropylene benzene, boiling range 284-2!34’, with S03.8 The material was found to be 96.797, pure (dry weight basis) by the method of Eptong based on cetylpyridinium broniide referred t,o dichromate. Sodium lauryl sulfiite (SDS) was synthesized by condensation of lauryl alcohol with chlorosulfonic acid in ether. (Calcd. for C,zHn&WrNa: C, 50.0; H, 8.7; S, 11.1. Found: C, 49.7; H, 8.5; S, 11.2). Soxhlet extraction with light petroleum mas used to reduce t,he minimum in the curve of surface tension with concentration. Sodium p-nonylbenzene sulfonate was prepnred by synthesis from pelargonyl chloride by Friedel-Crafts condensation with benzene followed by reduction with hjdrazine and sulfonation. (Calcd.: C, 58.8; H, 7 . 5 . Found: C, 57.95; H, 8.3.) It was purified by recrystallization from ethanol. A.R. grade NaCl was used at a constant concentration of 0.2 AI, and solutions were made in distilled water which had been passed over a fresh bed of Bio-deminrolit.
Results and Discussion Sodium p-nonylbenzene sulfonate had no minimum iii its ?/log C curve after purification (Fig. 1, I). The addition of 0.5% of a third component, lauryl alcohol, resulted in the appearance of a pronounced minimum (Fig. 1, 11). Repetition of the cxperiment with added alcohol in 0.2 ilP sodium chloride essentially removed the minimum (Fig. 1 111). The absence of a miiiimum in the preseiice of salt ( I ) C. Robinson in, “ F e t t i n g R. Detergency,” Harvey, London, 1937. p. 137. (2) D. Reiehenberg. Trans. Faraday SOC.,43, 407 (1047). (3) E. J. Clayfield and J. B. hIatthems, “Proc. 2nd Cong. Surface Activity,” Butternorth, London, 1957. Vol. 1, p. 172. (4) A. P. Brady, THIS JOURNAL, 53, 56 (1949). ( 5 ) E. F. W i l l i ~ ~ i i N. s , T. Woodberiy and J. IC. Dixon, J . Colloid Sci.. 12, 452 (0) J. D. Miles and L. Shedlovsky. TIIISJOURNAL, 48, 57 (1944). (7) W. D. Harkins and H. F. Jordan, J . A m . Chem. Soc.. 52, 1751
Internat.
(1857).
(1930). (8) 0 . K. Ashforth. prirntr roniiiiunication. (9) S. R. E p t o n . l’rons. Faraday SOL’., 4 4 , 22G (19.18).
lauryl alcohol; 111, plus 0.5% lauryl alcohol in 0.2-M NaCl
3G
34 I
i 32 0
n
Bx
r:
p 30
2s
26
-3 -2 log mo1:irity. Fig 2.-Surface tcnsion of sodium tetrxpropj lene benzene sulfonate: I, in distilled water a t 20”; 11, in 0.2 M XaC1. -4
wncl also found for ABS (Fig. 2) whcre the minimum without salt is probably due to the presence of sei.eral closely related alkyl benzenes, and for SDS (Fig. 3) where the minimum without salt is proba l ~ l ydue to traces of lauryl alcohol. An explanation is offered based on the treatment of adsorption a t the fluid/water interface given by Reichenberg. 2. No Salt.-The Gibbs equation for adsorption a t the air/water interface for an ionized surface active agent (det.) containing a small amount of impurity, e.g., lauryl alcohol (alc.) may be written - d r = rdet-dwet- 4- h a + d m n +4- raiodplnio 4hf-thofl-
rHaO+dfiHlo+
(1)
where y is the surface teiisioii aiid I? the surface
