An Investigation of Certain Properties of Hydrous Lanthanum

AN INVESTIGATION OF CERTAIN PROPERTIES OF HYDROUS LANTHANUM HYDROXIDE SOLS’ THERALD MOELLER’

AND

FRANCIS C. KRAUSKOPF

Downloaded by UNIV OF PENNSYLVANIA on September 15, 2015 | http://pubs.acs.org Publication Date: March 1, 1939 | doi: 10.1021/j150390a009

Laboratory of General Chemistry, University of Wisconsin, Madison, Wiscowin Received July 80, 1958 INTRODUCTION

Hydrous lanthanum hydroxide sols have been prepared by several investigators. The methods used have included dialysis after the addition of small amounts of ammonia to lanthanum acetate solutions (6, l), electrolysis of a lanthanum chloride solution using a mercury cathode (14), peptization of the freshly precipitated and well-washed hydroxide with dilute hydrochloric acid (2, 9), addition of less than 2.6 equivalents of sodium hydroxide to solutions of lanthanum nitrate or chloride (3, 17), and the “peptization” of lanthanum hydroxide with sucrose or levulose (18). Inasmuch as detailed studies on colloidal lanthanum hydroxide have been limited to x-ray proof of the crystallinity of the sol particles (2), some viscosity measurements (9), and recognition of the colloidal nature of the color reaction between lanthanum hydroxide and iodine in the presence of acetate (5, 1, 13, 12), it was felt that an examination of a few characteristics of these sols would be of value. PREPARATION AND PURIFICATION OF SOLS

Of the preparative methods previously reported, peptization of a boiling suspension of lanthanum hydroxide with dilute hydrochloric acid is the most satisfactory. However, this method necessitates the use of freshly precipitated hydroxide, and the comparatively long time required for the production of even moderately concentrated sols brings about aging effects which render the precipitate very resistant to the action of the peptizing agent. A method eliminating these difficulties has been described (16). Data for some of the sols prepared by this procedure and dialyzed with carbon dioxide-free water (16) are given in table 1. I n each instance the purity ratio is to be taken as the ratio of the equivalents of lanthanum oxide present to the equivalent of chloride. 1 This paper is a portion of a thesis submitted by Therald Moeller to the Faculty of the Graduate School of the University of Wisconsin in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1938. du Pont Fellow, 1937-38. Present address: Kedzie Chemical Laboratory, Michigan State College, East Lansing, Michigan.

a@

364

THERALD MOELLER AND FRANCIS C. KRAUSKOPF


ABSORPTION OF CARBON DIOXIDE

The impossibility of purifying hydrous lanthanum hydroxide sols by dialysis with water containing dissolved carbon dioxide and the necessity of protecting sols from the air have been discussed (16). Since lanthanum carbonate is insoluble and settles out when it forms, the absorption of carbon dioxide by a sol exposed to the air can be followed by periodic analyses for the lanthanum hydroxide remaining in suspension. Observations upon two portions of sol 6f, one exposed to the air and the other protected by a p a r a h seal, showed that the protected sol TABLE 1 Data for lanthanum hydroxide sols NHiOH PER CENT OF EQUIVALENT

TIME DIALYZED.

hour8

6c. . . . . . . . . 6d. . . . . . . . . 6e . . . . . . . . . 6f . . . . . . . . .

33.3 33.3 33.3 33.3

6h(l). . . . . . 6h(2). . . . . . Bh(3). . . . . . 6i. . . . . . . . . 6j . . . . . . . . . 6kt. . . . . . . . 617.. . . . . . 6m . . . . . . . . 6nt. . . . . . . . 6x. . . . . . . . . By. . . . . . . . . 6s. . . . . . . . .

50.0 67.0 89.0 50.0

6g . . . . . . . . .

40 45 48 51 84

80.0

67 67 67 85 80

80.0

80

87.5 87.5 33.33

41 41 120

P u R m RATIO

c1pama pcr

lik

0.250 0.500 0.829 0.755 0.438 1.158 1.984 2.312 0.736 2.121 0.766 0.732 1.406 1.492 4.04 3.99 0.553

ram8 per

litm

0.023 0.017 0.034 0.037 0.011 0.103 0.061 0.049 0.015 0.056 0.006 0.024

0.031 0.031 0.058 0.061 0.015

3.6 9.6 8.0 6.7 13.0 3.7 10.6 15.4 16.0 12.4 41.8 10.0 28.7 15.7 22.8 21.4 12.1

6.9 7.0 7.4 7.3 7.8 8.3 7.9 6.6

* All sols dialyzed at 20-25°C. except 6i, 6j, 6m, 6x, and 6y, which were dialyzed a t 35-40'C. t These sols were residues from other sols. remained unchanged in concentration for sixteen weeks, whereas the unprotected sol began to deposit lanthanum carbonate after two weeks and was completely destroyed after twenty-four weeks. THE STABILITY OF LANTHANUM HYDROXIDE a o L s AS MEASURED BY FLOCCULATION VALUEB

A. Experimental technique Flocculation values were determined as follows: Into carefully cleaned Pyrex test tubes varying amounts of the electrolyte solutions were meas-


HYDROIJB IANTHANUM HYDROXIDE BOLS

365

wed by means of a microburet. Sufficient carbon dioxide-free distilled water to make a total volume of 5 ml. was added to each from another microburet, followed by 5 ml. of the sol. Each tube was shaken vigorously and stoppered. Observations were made after 2 hr. The flocculation value for a given electroyte was thenobtained fromthat concentration of electrolyte midway between the least amount necessary for complete flocculation and the next smaller amount. The results have all been calculated as millimoles of electrolyte per liter of combined sol and electrolyte solution, and are to be interpreted as the liminal concentrations which just cause complete coagulation after 2 hr. The values were easily reproducible in all cases. In order to minimize the effects of carbon dioxide, carbon dioxide-free water was used for all solutions, and the sols were placed in flasks from which they could be transferred to 5-ml. burets in an atmosphere of carbon dioxide-free air. Most of the electrolytes used were of Merck reagent or Mallinckrodt analytical reagent grade. A few were C.P. salts and were purified by repeated recrystallization from doubly distilled water. Calibrated flasks and weights were used throughout.

B. Effect of sol purity From the method of preparation, it seems likely that lanthanum hydroxide sols are stabilized by lanthanum chloride, or more particularly by lanthanum ion. If this be true, then the stability of a sol should be a function of the amount of lanthanum chloride present. Furthermore, the flocculation values should, in general, increase as the purity ratio decreases, assuming equal sol concentrations, for the smaller the purity ratio, the larger the amount of stabilizing electrolyte present. Both of these statements have been verified. Interesting results upon the effect of sol purity were obtained during an attempt to investigate the influence of pH upon sol stability. Since Hazel and Sorum (10) had shown that the stability of ferric oxide sols is increased by increasing the hydrogen-ion concentration with hydrochloric acid, it was thought that hydrous lanthanum hydroxide sols might show the same behavior. Accordingly, samples of sol 6e were diluted as shown in table 2, the pH being determined on each portion with a glass electrode. Flocculation values determined upon these portions are summarized in table 3. Except with lanthanum chloride, monobasic potassium phosphate, and potassium ferrocyanide, there is a general increase in flocculation value with decrease in pH. This increase is quite steady until portion 5 is reached, but between portions 4 and 5 and 5 and 6 a sudden and very marked increase in stability occurs in a pH range of only 0.33. It seems odd for a so1 of this type that such a pronounced change in stability should occur in such a small pH interval, especially since between por-

366

THERALD YOELLER AND FRANCIS C. KRAVSKOPF

tiom 1 and 2, where the pH change is a trifle greater, only slight changes in stability are noted. Ferric oxide sols show no such tendencies. The slight pH changes and the highly basic nature of lanthanum hydroxide suggested that the acid which was added had reacted with the colloidal particles, converting them into stabilizing lanthanum chloride.


TABLE 2 Dilution of 801 6e DILUTED W I T E

Equal Equal Equal Equal Equal Equal

volume of v6lume of volume of volume of volume of volume of

water

M / W HCl M/2000 HCl M/1000 HCl M/500 HC1 M/250 HCl

7.43 7.03 6.85 6.67 6.56 6.34

TABLE 3 Flocculation values for sol Be 0

POSTION

..........................

1 Lacla. . . . . . . . . . . . . . . . . .

FLOCCULATIONVALUE. IN MILLIMOLES PEE LITES

ELBCFBOLTTE

KCl. . . . . . . . . . . . . . . . . . . . KBr .................... K I . .................... KNOs . . . . . . . . . . . . . . . . . . LiCl . . . . . . . . . . . . . . . . . . . KF ..................... Na804. . . . . . . . . . . . . . . . . KISO~.................. MgSOc . . . . . . . . . . . . . . . . . KsCr04. . . . . . . . . . . . . . . . . KaCraO,. ............... KHIPO~................ K&O4., ............... I(aP04.. . . . . . . . . . . . . . . . . KdFe(CN)a. ............

8.5 9.5 0.115 0.105 0.105 0.045 0.038 0.068 0.048 0.028 0.007

115 11.5 17 13 17.5 0.155 0.145 0.145 0.075 0.043 0.128 0.088 0.063 0.009

115 120 20 29 22 27 25 32 25 23 22.5 27 1.1 1.05 0.175 0.185 0.165 0.175 0.155 0.165 0.095 0.085 0.058 0.053 0.150 0.153 0.128 0.160 0.153 0.053 0.009 0.010

49 46 40 37 38 1.55 0.215 0.205 0.205 0.120 0.068 0.143 0.430 0.270 0.006

84

76 66 58 51 2.45 0.335 0.325 0.330 0.200 0.103 0.130 0.700* 0.450

0.005

Does not appear in figure 3.

If this were true, the flocculation values should then bear some relation to the amount of lanthanum chloride formed or to the hydrochloric acid added. In table 4 are given data relative to the amounts of acid added and the lanthanum chloride produced, assuming exact equivalence. Since the

367

HYDROUS LANTHANUM HYDROXIDE SOLS

lanthanum chloride content is increased much more between portions 4 and 6 than between the other portions, a comparatively large increase in stability should occur in this interval. Data from table 3 are plotted against the calculated lanthanum chloride contents from table 4 in figures 1, 2, and 3. For all electrolytes except


TABLE 4 Impurities in 801 6e FINAL EYDROCHLORIC ACID CONCENTRATION

PORTION

1

LANTEANUY CHLOBIDE EQUIVA-

LENT TO EYDROCHMBIC ACID

millimdas per l i t e

miUirndas par liter

2 0

0

0

0.125 0.250 0.500 1 .000

0.042 0.084 0.167 0.333

2.000

0.667

00

I

J 60

!

$

40

2

0

13

20

u

0 L

-

n

0

0.1

0.Z

0.3

LANTHANUM C H L O R I D C

-

0.4

03

MILLIMOLS/

0.6

E

0.7

R

FIG.1. Effect of sol purity upon etability

monobasic potassium phosphate and potassium ferrocyanide the flocculation values increase smoothly with sol impurity, there being no sudden breaks in the curves, thus supporting the contention that the increased stability upon the addition of hydrochloric acid is due to the formation of lanthanum ion in the sol. The shape of the curve seems to be somewhat dependent upon the val-

388

THHIRAIID MOELLEB AND EFBANCIS C. KBAUSKOPF

ence of the anion of the flocculating electrolyte. Several other pointa of interest are to be noted. First, the curves for potassium chloride, potas-

fl 0’

03 O 3

I

I SOL

I

I cc

I

0.4


f 2 E 0.s t

fl

ai.

z 0

5

0.1

3

u A

0.1 0.1 0.) 0.4. 0.8 LANTHANUM CHLORIDL 5MILLIROLS/

0.6

0.7

LlTER FIG.2. Effect of sol purity upon stability

LANTHANUM CHLORIDE

-

M l L L l f l O L S / ~

Fro. 3. Effect of sol purity upon stability mum bromide, and potassium iodide all cross at a common point.

At

this intersection a reversal in the order of effectiveness of the three halidea as flocculating agents occurs. The reason is obscure.

369

HYDROUS LlLNTHANUlld HYDROXIDE SOLS


Second, the values for the three sulfates lie along a common,curve, indicating that the nature of the cation is of almost negligible importance in flocculating the sols. Third, the order of relative effectiveness of the salts as flocculating agents seems to be a function of sol purity. Thus the order of decreasing flocculation values for the original is

while for the most impure sol it is

TABLE 5 Effect of lanthanum chloride upon ficculation values for sol 6k

K&PO4. . . . . . . . . . . . . . . . . K&O+. . . . . . . . . . . . . . . . . . K,Po4. . . . . . . . . . . . . . . . . . . KIFe(CN )6. . . . . . . . . . . . . . . K 9 e (CN)I. . . . . . . . . . . . . . .

0.05 0.048

0.170 0.140

0.018 0.013 0.008

0.083 0.018 0.012

0.230 0.230 0.145 0.021 0.015

the most surprising changes being with tribasic potassium phosphate and potassium arsenate. Fourth, the curves for monobasic potassium phosphate and potassium ferrocyanide show unexplained maxima. Lanthanum chloride exerts a similar stabilizing effect. Data obtained for sol 6k,which are given in table 5 and figure 4, sho,w a close parallel to those values for hydrochloric acid in equivalent regions. Again the behavior of monobasic potassium phosphate is peculiar.

C. Effect of dilution Although the application of the Burton-Bishop rule (4) to hydrous oxide and hydroxide sols has been disputed, Sorum and his coworkers (11, 7) have shown that while highly purified ferric oxide and chromic oxide sols follow the rule, treatment with ferric and chromic chlorides, respectively, causes them to require decreasing amounts of all electrolytes for floccula-

370

THERALD MOELLER A N D FRANCIS C. KRAUSKOPF

tion after dilution. It will be shown that hydrous lanthanum hydroxide sols exhibit the same characteristics.


d i

0.2

2

r

z

0 < 2

0 0 D

O

FLOCCULATION VALUE, IN MILLIMOLE8 PER U T E R

ELECTEOLYTm K) per can

IO per cenl

10 per cent

-I

14 11 0.30

12 10 0.35

11 9 0.40

10

1. Monovalent anions:

KBr ........................ KCI, . . . . . . . . . . . . . . . . . . . . . . . . KF ......................... 2. Divalent anions: KiSO4. ...................... KlCrOd. .................... K&1*0r. .................... 3. Trivalent anions: KsASO4. .....................

&Po4. ..................... 4. Tetravalent anion: K4Fe(CN)a.. . . . . . . . . . . . . . . . .

0 per cent a0 per cant

9.5 0.45

* * 0.60

0.165 0.075 0.060

0.165 0.075 0.060

0.165 0.075 0.060

0.043 0.028

0.038 0.023

0.032

0.025 0.014

0.018

0.018

0.006

0.004

0.003

0.004

0.002

0.160 0.075 0.060

0.170 0.075

0.060 0.008

* Sol too dilute for accurate observations. Flocculation values obtained for sol 6i are summarized in table 6, where sol concentrations are expressed as per cent of the original sol


HYDROUS 'LANTHANUM HYDROXIDE SOLS

CONCeNTRATlON

4 b O R I Q I N A L SOL

FIG.5 . Effect of dilution upon sol stability

371

372

THERALD MOELLER AND FRANCIS ‘C. KRAUSKOPF


present. Some of these data are plotted in figures 5 and 6. This sol follows the Burton-Bishop rule for all electrolytes investigated except potassium chloride and potassium bromide. The effects of dilution after the addition of lanthanum chloride are shown in table 7, where the 100 per cent sol received 0.19 d i o l e of lanthanum chloride per liter and the others proportionally smaller

FLOCCULATION V A L U ~ , IN yILLmoma PEE LITEE ELICrEOLYTE

100 per cent

1. Monovalent anion: KF . . . . . . . . . . . . . . . . . . . . . . . . . 2. Divalent anions: K1s04........................ KzCrO,. ..................... KzCrtO,...................... 3. Tetravalent anion: K4Fe(CN)c.. . . . . . . . . . . . . . . . . .

Effect of dilution

20 per aant

0.88

0.65

0.60

0.30 0.155 0.095

0.23 0.125 0.070

0.25 0.115

0.008

0.004

0.002

0.055

TABLE 8 m flocculation valves of sol 6m -ULATION

la, per cent

1. Monovalent anion: KBr. ....................... 2. Divalent anione: KrSOc. ...................... K*CmO, ..................... 3. Trivalent anions: K&o4. .................... & P o i . ..................... 4. Tetravalent anion: KrFe(CN)‘. .................

40 per cent

TALUE. m Y I L L I Y O ~

76 per mt

PEB DEB

60 per cent -

2.5

3.5

4.5

0.075

0.085 0.065.

0.095 0.065

0.043 0.023

0.043

0.023

0.038 0.023

0.006

0.006

0.005

0.065

amounts. Decreasing amounts of all electrolytes are required as the sol is diluted. Further evidence of the application of the Burton-Bishop rule to highly purified sols is given in table 8. Here potassium bromide also followed the rule, but the effects were less noticeable with the anions of higher valence, perhaps because of the greater purity of this so1 (see table 1). Data in table 9 show that again the addition of lanthanum chloride caused the sol to exhibit “normal effects” upon dilution. Again the 100 per cent sol was

373


treated with 0.19 millimole of lanthanum chloride per liter and the others with proportionally less.

D. E$& of alcohol


If the stability of a hydrous oxide or hydroxide sol be due in part to hydration, the addition of a dehydrating agent such as alcohol or acetone TABLE 9 Effect of dilution upon 801 6m (treated)

1I

ELECrBOLlTE

1. Monovalent anion: KBr.. ....................... 2. Divalent anions: KISO~. ...................... K&r:O, ..................... 3. Trivalent anions: KrAsOi. .................... K I P O ~...................... . 4. Tetravalent anion: K4Fe(CN)a.. . . . . . . . . . . . . . . . . .

FLOCCULATION VALUE, I N MILLIMOLE8 PER LITER

100 per cent

7.5 per cent

29

34 0.8

50 per cent

25

0.115

0.24 0.105

0.21 0,085

0.243 0.133

0.173 0.103

0.118 0.073

0.021

0.016

0.011

TABLE 10 Effect of alcohol upon sot 61 5rcrBOLTTB

KCI, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . KF . . . . . . . . . . . ..................... Kzs04. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . KzCrO4. .................................... K&rzO,. .................................. KaAsOi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... KrFe(CN)a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sol 61(3)

%I 61(3)’

25

22 0.85 0.15 0.115 0.08 0.145 0.093 0.008

1.15 0.21 0.13 0.09 0.175 0.108 0.008

~

should render that sol more sensitive to flocculation by electrolytes. Reports in the literature are, however, conflicting (19). I n table 10 are summarized some flocculation values obtained with sol 61. A part of sol 61 was divided into two 750-ml. portions, one of which, 61(3), was treated with 250 ml. of water, and the other, 61(3)’, with 250 ml. of 95 per cent ethyl alcohol. With the exception of the ferrocyanide all anions, regardless of valence, were more effective in flocculating the sol treated with alcohol. However, the small differences

374

THERALD MOELLER AND FlUNCIS C. ICRAUBKOPB


in flocculation values between the two sols indicate that the dehydrating action was not very pronounced and that, therefore, only a small amount of the stability of lanthanum hydroxide sols can be ascribed to hydration, the major part being due to adsorbed lanthanum ion. Furthermore, neither alcohol nor acetone alone is capable of flocculating these sols, indicating the absence of excessive hydration.

E. Discussion From the results presented it may be concluded that the stability of lanthanum hydroxide sols is influenced chiefly by purity and sol concentration. The apparent impossibility of obtaining sols that give exactly the same flocculation values for a given salt is to be expected, for the conditions of dialysis could not be sufficiently accurately controlled to yield sols of constant concentration and purity. Consequently, no attempt has been made to ascribe to lanthanum hydroxide sols in general a definite flocculation value for each electrolyte. Each sol possesses its own stability and can be characterized by the flocculation values obtained for it. The data for sol 6e have indicated that the lyotropic order depends somewhat upon sol purity. Taking this into account and using only the results for the more nearly pure sols, it has been possible to compile the following series for the potassium salts, in which the anions are arranged in order of increasing flocculation values: ferrocyanide, ferricyanide, tribasic phosphate, arsenate, dichromate, monobasic phosphate, chromate, sulfate, fluoride, nitrate, chloride, bromide, and iodide. The arrangement in this series agrees well with those reported for ferric oxide (10) and beryllium oxide (15) sols. The values for lanthanum hydroxide are of the same magnitude as those for ferric oxide but are much smaller than those for beryllium oxide. By analogy to other sols, it is probable that the stabilizing lanthanum ion is adsorbed on the suspended particles. Since Bohm and Niclassen (2) have shown that the sol particles give the same x-ray pattern as precipitated lanthanum hydroxide, it is likely that these particles, too, are lanthanum hydroxide. HYDROUS LANTHANUM HYDROXIDE SOLS AND THE IRREGULAR SERIES

Flocculation studies with tribasic potassium phosphate indicated that lanthanum hydroxide sols containing considerable phosphate flocculate much more slowly than those containing smaller quantities of the electrolyte. Such observations suggested a n irregular series, and it was found that lanthanum hydroxide sols are recharged by tribasic potassium phosphate. A series of experiments was carried out with sol 6k. This sol was di-

375



vided into three portions, which were treated as indicated in table 5. Five-milliliter samples of these sols were observed in the presence of increasing concentrations of several electrolytes yielding polyvalent anions, according to the method used for the determination of flocculation values. The results are given in table 11. Of the electrolytes investigated, only the tribasic phosphate gave an irregular series. I n no other instance was there any evidence of a recharging effect. For the tribasic phosphate, TABLE 11 Thc irregular series jor sol 6k I ELECTROLYTE

1

CONCENTRATION I N

1 MILLIMOLE0 PER LITER

oBOERvATIoNB ('

*'"

I

j

ILECTROPRORETIC MIGRATION

A. Sol 6k(l) 1. K I P 0 4 . . . . . . . . . . . . . . . .

2. KHIPOI . . . . . . . . . . . . . .

0 t o 0.018 0.018 to 0.215 0.215 to 95 95 up

No coagulation Complete coagulation No coagulation Complete coagulation

0 to 0.05 0.05 to 50

No coagulation

3. KaAsOd. . . . . . . . . . . . . . .

To cathode

To anode To cathode

Complete coagulation No coagulation Complete coagulation

To cathode

0.048 to 50

4. K3Fe(CN)e.. . . . . . . . . . .

0 to 0.013 0.013 to 50

No coagulation Complete coagulation

To cathode

5. K4Fe(CN)6

0 to 0.008 0.008 to 50


To cathode

0 to 0.048

-

B. Sol 6k

)

0 to 0.083 0.083 to 0.75 0.75 to 37 37 up

No coagulation Complete coagulation No coagulation Complete coagulation

To cathode

2. KHnPOi . . . . . . . . . . . . .

0 to 0.170 0.170 to 50


To cathode

3. KaABO4. . . . . . . . . . . . . .

0 to 0.140 0.140 to 50


To cathode

4. K3Fe(CN)s. . . . . . . . . . .

0 to 0.018 0.018 to 50


To cathode

0 to 0.012


To cathode

1. KaPOd

5. K4Fe(CN)s. . . . . . . . . . .

0.012 to 50

To anode

376

THERALD YOELLER AND

FRANCIS C. KRAUSKOPF

TABLE 11-Continued The irregular series jor sol 6k C. Sol 6k(3)


. , .... . . .. . . .

No coagulation

To cathode

Complete coagulation No coagulation Complete coagulation

To anode

0 to 0.230 0.230 t o 50

No coagulation

To cathode

3. KaAsO4.. . . . . . . , . , . . .

0 to 0.230 0.230 to 50


To cathode

. . .... .. . .

0 t o 0.021 0.021 to 50


T o cathode

5. KdFe(CN)s. . . . . . . . . . .

0 to 0.015 0.015to 50


To cathode

1. KSPO,.

2. KHgPO,.

,

. . . . . . . . ... ..

4. KaFe(CN)s.

0 to 0.145 0.145 to 1.0 1.0 to 31 31 up

Complete coagulation

the narrowed stability range for the negative sol with increasing lanthanum chloride concentrations is to be expected, for the lanthanum ion will add its zeta potential-raising power to that of the potassium ion and thereby promote flocculation of the negative sol at lower potassium phosphate concentrations. Observations upon another sol indicated that dibasic potassium phosphate gave evidences of a slight recharging effect. Thus for lanthanum hydroxide sols it appears that the tribasic phosphate ion is specific in producing the irregular series, and in the series tribasic phosphate, dibasic phosphate, monobasic phosphate the recharging effects decrease with decreasing concentrations of Pod--- ion. Negative lanthanum hydroxide sols, while resembling the positive sols in appearance, are much less stable and flocculate after 24 to 36 hr. DENSITY MEASUREMENTS

With regard to the density of a hydrophobic sol, FreundKch (8) states that it “may be represented by a linear equation” dependent upon sol concentration. Results of density determinations upon sols 6x and 6y are given in table 12 and figure 7. The original sols were diluted to the desired concentrations with carbon dioxide-free distilled water, and the values were obtained with a calibrated 10-ml. pycnometer at 25°C. & 0.01O. All data are referred to 4°C. Thus the densities of hydrous lanthanum hydroxide sols vary linearly with the amount of the dispersed material.

377

HYDROUS LANTHANUM HYDROXIDE SOLS MISCELLANEOUS

Hydrous lanthanum hydroxide sols exhibit a well-defined Tyndall effect, and the particles may be distinguished as points of light with the ultramicroscope. TABLE 12


Density measurements

/I

Sol 82

Lato:

Sol By

DENBITT

pram6 psr liter

gram8

4.04 3.64 3.23 2.83 2.42 2.02 1.62 1.21 0.81 0.40

DENIlITT

grama pa liter

per cc.

3.99 3.59 3.19 2.79 2.39 2.00 1.60 1.20 0.80 0.40

1.0005 l.* 0.9998 0.9994 0.9991 0.9988 0.9984 0.9981 0.9977 0.9973 0.9970

0

grama p s r cc.

1.0003 1 .oooo 0.9995 0.9991 0.9989 0.9987 0.9985 0.9980 0.9977 0.9972 0.9970

0

1.001

$1

1.000

\

il 0

0.qqq

0.997 1

2

CONCENTRATION

-

3

+

5

GMB L*S/LlTER

FIG.7. Density of sols Undialyzed sols may be boiled or frozen without flocculation. Dialyzed sols, however, are readily coagulated. by boiling or freezing. The coagulum from a boiled sol is crystalline and finely divided, indicating the aging effects of heating.

378

THERALD MOELLER AND F‘RANCIS C. KFZAUSKOPF


SUMMARY

1. Stable lanthanum hydroxide sols have been prepared and purified by dialysis. 2. All sols absorb carbon dioxide from the air. The reduction in sol concentration due to carbonate formation has been followed. 3. The stability of the dialyzed sols, as measured by flocculation values, has been investigated under a variety of conditions. The addition of lanthanum chloride or hydrochloric acid stabilizes the sols. Very pure sols follow the Burton-Bishop rule, but the addition of small amounts of lanthanum chloride causes these sols to exhibit “normal” effects upon dilution. Alcohol exerts a sensitizing effect. 4. A lyotropic series has been set up. 5. An irregular series has been found for tribasic potassium phosphate, but not for similar electrolytes. The addition of lanthanum chloride narrows the region of stability of the negative sol. 6. The densities of lanthanum hydroxide sols vary linearly with sol concentration. 7 . A few qualitative observations have been given. REFERENCES (1) BILTZ:Ber. 37,719 (1904). (2) BOHMASD NICLASSEN: Z. anorg. Chem. 132,1 (1923). (3) BRITTON:J. Chem. SOC.127, 2142 (1925). (4) BURTON AND BISHOP:J. Phys. Chem. 24, 701 (1920). (5) DAMOUR: Compt. rend. 43,976 (1856). (6) DELAFONTAINE: Chem. N e w 73, 284 (1896). (7) FISHER AND SORTJM:J. Phys. Chem. 39,283 (1935). (8) FREUNDLICH: Colloid and Capillary Chemistry, p. 365. E. P. Dutton and Co., New York (1926). (9) FREUNDLICH AND SCHALEK: Z. physik. Chem. 108, 153 (1924). (10) HAZELAND SORUM:J. Am. Chem. SOC. 63,49 (1931). (11) JUDD AXD SORUM:J. Am. Chem. SOC.62, 2598 (1930). (12) K R ~ C EAND R TSCHIRCH: Ber. 82B,2776 (1929). (13) LOTTERMOSER: Kolloid-Z. 33,271 (1923). (14) MCCUTCHEON AND SMITH:J. Am. Chem. SOC. 29, 1460 (1907). (15) MADSON AND KRAUSKOPF: J. Phys. Chem. 36, 3237 (1931). (16) MOELLERAND KRAUSKOPF: J. Am. Chem. SOC.80, 726 (1938). (17) SADOLIN:Z. anorg. Chem. 160, 133 (1927). (18)SEN: Z.anorg. allgem. Chem. 174, 61 (1928). (19) THOMAS:Colloid Chemistry, p. 195. McGraw-Hill Book Co., New York (1934).

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An Investigation of Certain Properties of Hydrous Lanthanum

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