Coagulation and reversal of charge of lyophobic colloids by hydrolyzed metal ions

Coagulation and Reversal of Charge of Lyophobic Colloids by Hydrolyzed Metal Ions V. ScandiumNitrate~'2 E G O N M A T I J E V I C , A L B E R T B. L E V I T } AND G I L B E R T E. J A N A U E R 4 Institute of Colloid and Surface Science and Department of Chemistry, Clarkson College of Technology, Potsdam, New York 13676 and Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13901

Critical coagulation concentrations and critical stabilization concentrations of scandium nitrate solutions for negatively charged silver bromide sols in statu nascendi were obtained over the pH range 3-7. The concentrations of all scandium species present in solution over the same range of salt concentration and of pH were calculated using the hydrolysis constants recently determined by Aveston (14). It could be shown that the stability phenomena observed are directly related to the composition of the scandium salt solution. INTRODUCTION In the previous papers of this series, it was shown that the hydrolysis of metal ions has a profound effect upon the stability of negatively charged lyophobic sols. The critical coagulation concentration (c.c.c.) of salts containing hydrolyzable cations changes With p H in a manner which is determined by the composition and the concentration of various counterion species. In addition, hydrolyzed ions adsorb very strongly and may reverse the charge of the sol particles if present in sufficient amounts. The correlation between the change in the c.c.c, with pH and the change in the composition of the electrolyte solution is rather simple in cases when the hydrolysis yields one predominant species only. This is particularly true if the hydrolyzed complex has a charge higher than the corresponding unhydrolyzed counterion. Indeed, under 1 Part IV, see reference 1. 2 Supported in part by the Federal Water Pollution Control Administration, Grant WP-00815. s National Science Foundation Undergraduate Research Participant. 4SUNY Research Foundation Grant 1965/ 1966.

these conditions, stability phenomena can be utilized to detect and formulate the composition of the hydrolyzed species. As an example, the work involving aluminum salts is mentioned here which resulted in the establishment of the composition of an octameric aluminum hydrolyzed ion, AIs(OH)~+ (2), and of the basic aluminum sulfate complex, Als(OH)10(SO4) 4+ (3). When the hydrolysis process produces several different species, the relationship between the stability phenomena and the composition of the electrolytic medium becomes rather involved. One reason for the difficulty is that frequently inadequate thermodynamic data are available and therefore the composition of the electrolyte solution is not known with certainty. The second reason is that the effects of a mixture of counterions upon the stability of lyophobie sols are not well understood at present. I t seems, then, that a study of the coagulation and charge reversal phenomena of a lyophobic sol in an electrolyte medium which contains various hydrolyzed species of well-known composition and concentrations would be of great interest in furthering the understanding of colloid stability. The

Journal of Colloid and Interface Science, Vol. 28, No. I, September 1968

10

COAGULATION AND CHARGE REVERSAL OF LYOPHOBIC COLLOIDS hydrolysis of scandium ion has been studied extensively and sufficient information is available to calculate the composition of its solutions as a function of concentration and pH. Therefore, the investigation of the behavior of a silver bromide sol in statu naseendi in solutions of scandium nitrate over a p H range 3-7 was undertaken. The entire [Sc(NO3)a]-pH domain was obtained giving the regions of uneoagulated, coagulated sols, and sols stabilized owing to charge reversal. It will be shown that the phenomena observed are directly related to the composition of the scandium sMt solution. EXPERIMENTAL 1. Materials. Scandium nitrate, Sc(NQ)~, 99.9 % pure ( " K and K " Laboratories), was used. To prevent hydrolysis, the stock solutions of this sMt (2 X 10-ZM) were acidified with nitric acid to a p H of 1.5. No aging was noticeable during the storage for one month at 25°C. All other ehemicMs were of the highest purity grade commercially available. Solutions were prepared with doubly distilled water. The silver bromide sols in statu naseendi contained 2.0 X 10-~ moles/liter AgBr and an excess of 2.0 X 10-~ moles/liter KBr. Aged silver bromide sols for electrophoresis measurements were prepared by adding

11

silver nitrate solutions to vigorously stirred potassium bromide solutions, which were then maintained at 80°C for 18 hours and filtered through No. 40 W h a t m a n filter paper (2). 2. Methods. The critical coagulation concentration (c.c.c.) and the critical stabilization concentration (c.s.c.) were determined from the measurements in the change of scattering intensities as described earlier (4, 5). The electrophoresis measurements were carried out in a Mattson type celt with an ultramicroscope (2). A few experiments were made to establish the conditions for precipitation of scandium hydroxide. Varying amounts of sodium hydroxide were added to test tubes containing solutions of constant concentrations of scandium nitrate. The precipitation boundary was established by measuring the scattering intensities over extended periods of time. A Beckman Model G p H meter with a glass electrode was used for the measurements of pH. The instrument was calibrated regularly with appropriate buffer solutions. RESULTS Since the stability of a lyophobic sol in the presence of a hydrolyzable electrolyte depends on two parameters, i.e., salt con-

.72

t hgBr; 2.0"10 "4 M

S

~

I2

KBr ' 2.0"10 "4 M

A

>Iz.48 LU I-Z

I

~J

~.24

°, 10 rain.

-I0

8

4

--2

0 3.0

3.5 -LOG.

4,0 MOLAR

4.5 CONC. OF S¢(NO~)~

5,0

0

FIG. 1. Coagulation curves of a silver bromide sol in statu nascendi in the presence of various amounts of scandium nitrate, 10 minutes after mixing the reacting components. Full lines and open points represent turbidity measurements; A denotes the coagulation limit and B the stabilization limit. Dashed curves and blackened points give the corresponding pH values. Concentrations: AgBr: 2.0 X lO-4M, excess KBr: 2.0 X 10-4M. Journal of Colloid and Interface ~cience, Vo]. 28, N o . 1, S e p t e m b e r 1998

12

MATIJEVIC, LEVIT, AND JANAUER

centration and pH, the experiments can be carried out in two different ways. One can prepare a number of systems containing the same sol and systematically vary the concentration of the electrolyte from system to system keeping p H constant (or controlled). Alternatively, a p H gradient can be produced in a series of systems by addition of an acid or a base while the concentration of the salt is kept constant. Scattering intensities of each system are then measured and used to determine the concentration and pH conditions which produce either a coagulated or a stable sol. If scattering measurements are made before settling takes place, high values, as a rule, indicate coagulated and low values stable sols. In Fig. 1, the three curves show the change in the scattering intensities of a silver bromide sol in stat~ nascendi as a function of various amounts of added scandium nitrate. The corresponding p H values for each system are given with blackened symbols. Since the scandium nitrate stock solution was acidified to prevent aging, the p H adjustments were made by the addition of various amounts of NaOH. In these experiments no effort was made to keep the p H constant in a series of systems. Each curve Sz(N03)3,

AgBr,2.0.10-4M KBr: ~'.0.10-4M

1.0"i 0 - 4

>.48 LU Z

~

"0"1;0- 5 ~

2"5"10-6M

~9

z

~.24

03.0

4.0

5.0

pH

6.0

ZO

FIG. 2. Scattering intensity vs. pH of a silver bromide sol in statu nascendi in the presence of four different concentrations of scandium nitrate, 10 minutes after mixing the reacting components. Concentrations: AgBr: 2.0 X 10-aM, excess KBr: 2.0 X 10-~M; Sc(NO3)3:4.0 X 10-4]// ([~), 1.0 X 10-421// (/k), 3.0 X 10-5M (©), and 2.5 X 10-6M (O). C denotes the reversal of charge limit; D denotes the coagulation limit.

shows a rather abrupt decrease in scattering intensity below a certain concentration of scandium nitrate, indicating the transition from coagulated to uncoagulated sols. The extrapolation of this boundary ( " A " ) to zero scattering intensity gives the critical coagulation concentration (c.c.c.). The corresponding p H value can be obtained from the p H curve which refers to the same system. At low p H values only one transition between the stable and the coagulated sol (the curve designated b y circles) is ohserved. At higher p H values, two such boundaries are distinguished. The stability region above the concentration of scandium nitrate which is designated b y the limit " B " is due to charge reversal. An extrapolation to zero of the steep transition boundary between the high and low scattering intensity regions g i v e s the critical stabilization concentration (c.s.c.). Figure 2 shows scattering intensity vs. p H curves for several systems each containing a different but constant concentration of scandium nitrate. In this case, boundary ~ "C" gives the transition between the coagulated sols and sols stabilized owing to charge reversal. The c.s.e, is equal to the concentration of scandium nitrate in the system for a p H value obtained by extrapolating the limit "C" to zero scattering intensity. Sometimes plots as shown in Fig. 2 can also yield the c.c.c. For example, the boundary " D " in the curve given by the circles represerifs the transition between the stable, negative sol and the coagulated sol. The concentration of Sc(NO3)3 in this system corresponds to the c.c.c, at the p i t value obtained b y extrapolation of the limit " D " to zero scattering intensity. All'curves in Figs. 1 and 2 represent data obtained 10 minutes after the reacting components were mixed. Scattering intensities have been measured over an extended period of time (1-60 minutes), but the c.c.c, and the c.s.c, were only slightly dependent on time up to one hour. The reversal of charge b y hydrolyzed Scandium ions was confirmed by electrophoretic measurements. The three curves in Fig. 3 give the electrophoretic mobilities of an aged silver bromide sol as a function of

Journal of Colloid and Interf~tce Science, Vol. 28, No. 1, September 1968

COAGULATION AND CHARGE REVERSAL OF LYOPHOBIC COLLOIDS

AgBr/Br--

SOL

I

F

I

]t NOBILITY ATpH7.Z

[ I

--i-4,O[ -6.o[-

I

::!f'°'°': 3.0

=

. . . . . . .

4.0

5,0

6,0

pH

Fro. 3. Mobilities of an aged silver bromide sol (AgBr : 2.0 X 10-4M, excess KBr : 2.0 X 10-4M) in the presence of three different concentrations of scandium nitrate (1.0 X 10-4M top, 3.0 × 10-5M middle, 1.0 X 10-~M bottom curve) as a function of pH. Squares denote the mobilities of the same sol in the absence of Sc(NO3)3. pH. The concentration of the sol and of the excess B r - is the same as in the previous figures. Each curve is for a different but constant concentration of scandium nitrate. When the p i t is sufficiently high, charge reversal takes place in all cases. If mobilities are measured at still higher p H values ( > 6) the sol becomes again negatively charged. This is indicated b y the arrow in the middle p a r t of the diagram. To prove t h a t the changes in mobilities are due to the presence of scandium species, the mobilities of the same sol were determined as a function of pH, but in the absence of the Sc(N03)3. These results are given in the upper diagram as squares (dashed line). Figure 4 summarizes the data on the stability of a silver bromide sol in the presence of scandium nitrate at various concentrations as a function of p H . T h e circles designate the e.e.e.'s. Below this curve, the addition of Sc(N03)s has no effect upon the sol stability. Squares represent the e.s.c. To the right and above this line, the sols

13

are stabilized owing to charge reversal. I n the region between the two curves the sols are coagulated. I n order to properly interpret the data, it was necessary to establish whether insoluble scandium hydroxide is precipitated under the conditions of the [Sc(NO3)a]-pH domain in Fig. 4. Very limited information on the solubility of scandium hydroxide is available. Latimer estimated the solubility product for Sc (OH)a to be 1 X 10 -27 (6), whereas Kovalenko and Bagdarasov give Ksl, = 1.9 X 10 .28 (7). With the use of the latter value the precipitation limit of scandium hydroxide was calculated and plotted as the dotted line. This line falls between two other sets of data reported in the literature. St~rbat~Shm and Meliehar found t h a t the precipitation of scandium hydroxide begins at p H = 6.1 from a 0.01 M solution of scandium acetate (8), whereas IvanovE m i n and Ostroumov (9) observed the beginning of precipitation at p H 4.90 from 0.005 M SeCla or 0.0025 M Sc2(SO4)a. Our own few experiments, carried out to establish the precipitation limit of scandium hydroxide, were in reasonable agreement with the dotted line in Fig. 4. I t is obvious t h a t the entire coagulated range of the silver bromide sol is outside of the precipitation region of scandium -3.C AgBr =2.0.10-4 M KBr : 2.0.10-4 M i -4£

:',. [ '. / [3 STABILITY I. PREC~PIT.OF

\

~OA~g~o"~'o~ - . . j

"~

.coo o -S.C -

-6.(3 3D

-

R E B I ~ . Sc(OH)3

-

"0..

UNCOA!ULATED SO~ 7

4.0

5.0

\

pH

~ ".

~0

7.0

FIG. 4. The entire log [Sc(NO~)3]-pH domain for a silver bromide sol (AgBr 2.0 X 1 0 - 4 M , exc e s s KBr 2.0 X 10-4M). Circles denote the critical coagulation concentrations and squares the critical stabilization concentrations. Diamonds give the electrophoretic zero points of charge. Dotted line indicates the formation of scandium hydroxide in the absence of silver bromide.

Journal of Colloid and Interface Science, VoL 28, No. 1, September 1968

14

MATIJEVIC,

LEVIT,

AND

hydroxide. Also the e.s.c, boundary is reached before the precipitation of So(OH)3 sets in. Diamonds designate the zero points of charge as obtained from electrophoretic mobilities. These fall approximately in the middle of the coagulation range similarly to what was observed earlier in the presence of hafnium salts (10).

JANAUER

in scandium perchlorate solutions and established that the results can be best explained assuming the existence of the following complex ions: SeOH 2+, Sc2(OH)~ +, Scs(OH)~+, and Sc3(OH) 4+. All attempts to include more than these four species failed to improve the quantitative analysis of the results. Ultracentrifugation measurements showed no evidence of higher polymers than trimers and Aveston concluded that the "core + link" hypothesis is invalid. The hydrolysis constants for the various species reported in the literature are summarized in Table I.

DISCUSSION

Hydrolysis of Scandium Ion. Hexaquoscandium ion has an electron configuration resembling that of the hydrated aluminum ion. However, it is less basic and in many ways similar to the lanthanides, although it is much smaller in size. It is its smaller ionic radius which causes the scandium ion to hydrolyze much more strongly than the lanthanide ions. Several studies of scandium ion hydrolysis have been reported. Kilpatriek and Pokras (11) assumed two principal hydrolysis products: Sc0H 2+ and Scd0H) 4+. At higher pH values, they suggested the formation of a series of increasingly complex polymeric species. The data of Kilpatrick and Pokras were later recalculated using the "core q-links" model of the general formula Sc[(0H)~Sc](~ +n)+ (12). It was found that in addition to the two originally proposed complexes, the hydrolysis species Sc(0H)~ + and Sca(0H)~ + are also formed. The existence of the dimer Sc~(OH) 4+ and possibly of a tetramer Se4(OH)s~+ was suggested by Fromage and Faucherre (13). Recently, Aveston (14) carried out ultracentrifugation and acidity measurements

Analysis of Coagulation and Charge Reversal Data. It is expected that the coagulation of the silver bromide sol by scandium nitrate at various values of pH would depend on the hydrolysis of scandium ion. In order to establish whether a quantitative relationship exists between the composition of the electrolyte solution and the coagulation values, the concentration of all scandium species has been calculated for various values of pH and the total scandium nitrate concentrations corresponding to c.c.c. For this purpose, Aveston's hydrolysis constants (14) 'have been taken and are represented by the following set of equilibria: Sc 3+ 3- H20 ~- ScOH 2+ + H + log KII = -5.11 4- 0.09 2Sc 3+ q- 2H20 ~ Sc2(OH)~+ + 2H + log K22 = - 6 . 1 4 4- 0.02 3Sc 3+ q- 4H~O ~ ScdOH)45+ q- 4H + log K4~ = -13.00 4. 0.06

TABLE

I

~IYDROLYSIS CONSTANTS OF SCANDIUM SPECIES AT 2 5 ° C Ionic strength 1.0

ScOH~+

1 . 1 7 X 10 -5 8 , 0 X 10 - 6 7 . 8 X 10 - 6

0.5

1 . 2 5 X 10 -5 --

0.1

1 . 8 1 X 10 -5 --

0.01

2 . 4 5 X 10 -5 1 . 5 X 10 -4

Sc(OH)2+

Sc2(OH)~+

--

Sc~(OH)~+

Sca(OH)~ +

1 . 0 1 X 10 -6

--

7 X 10 -7 7 . 2 X 10 -7

-1 . 0 X 10 -13

--

1 . 2 7 X 10 -5

--

--

--

1.26

--

--

--

2 . 1 5 X 10 - 8

6 X 10 -~1 --

--

-.

1.6

.

X

X

10 -6

10 -6

4 . 4 7 X 10 -6 .

Journal of Colloid and Interface Science, VoL 28, No. 1, September 1968

.

--3 . 4 X 10 - i s

--

--

--

--

--

--

Ref.

11 12 14 11 12 11 12 11 15

3.2

4.2

2.9 X 1~ s

2 . 9 X 10-5

6.0

6.2

4 . 0 X 10 -6

3 . 2 X 10-6

1.8 X

4.0 t

10 7

10 -7

1.3 X 10-6 6.8

11.2

21.9

38.1

10-7

2 . 2 X 10-9

2 . 9 X 10 -6

4 . 5 X 10 6

5.5 X 10-6

6.1 X 10-6

5 . 7 X 10 -9

3.1 X 10 -~

3.5 X

[ScOH2+J

83.3

81.5

72.5

57.7

40.1

23.2

10.9

1.2

%

6.0 X

1.0 X

2.2 X

3.6 X

4.5 X

4.0 X

1.2 X

1.5 X

10 -s

10-7

10-7

10-7

10-7

10 -7

10 -7

10-9

[Sc2(OI-I)~+1

2.2

2.8

3.7

3.8

3.0

1.6

0.4

0

%

3.8 X

4.9 X

7.0 X

6.9 X

4.5 X

1.6 X

1.0 X

1.5 X

10-9

10-9

10-9

10-9

10-~

10 -9

10-1°

10-1~

[ScKOH)~+]

0.1

0.1

0.1

0.1

0

0

0

0

%

2.0 X

1.5 X

1.0 X

4.5 X

1.4 X

2.2 X

10 -7

10-7

10-7

10-s

10-s

10-9

5 . 6 X 10 -11

7 . 8 X 10 -16

iSc~(OH)t +]

7.6

4.3

2.1

0.5

0.1

0

0

0

%

© ~z

U~

o

o

d'

Dr~

©

5.6

6.3 X 10-6

3 . 6 X 10 9

56.8

75.2

88.7

98.8

%

o

5.3

1.0 X 10-~

8.7 X 10-6

1.9 X 10 - s

2 . 5 X 10-5

2 . 8 X 10-5

[Sca+]e

C~

d~ 0

5.0

1.6 X 10-5

4.6

pH

[Sc(NO3)a]tot

2 . 5 X 10-'~

II

o

.<

c~

c~

.%

TABLE

CALCULATED CONCENTRATIONS OF VARIOUS SCANDIUM SPECIES IN SOLUTION ALONG THE COAGULATION CURVE (C~RcL~S, F m . 4)

©

©

16

MATIJEVIC, LEVIT, AND JANAUER

3Sc 3+ + 5~20~-~ Sc3(OH)~ + + 5H + log K35 = --17.47 ~ 0.03 With the use of these equilibrium constants, the equation:

[Sc3+ho ~ = [Sc~+]e + K~[Sc~+]o/[I-I +] q- 2K2~[Sc3+]e2/[H+]~ q- 3K43[Sc3+]e3/[H+]4 3- 3Ks~[Sc3+]2/[H+]5 was solved with the aid of a computer for the points along the coagulation limit (circles) in Fig. 4. The results are given in Table II. Along the horizontal part of the curve (pH < 4.2) the c.c.c, is 3 X 10-SM, which value is characteristic for counterions of charge 3 + such as l a n t h a n u m (16, 17) or aluminum (2, 16, 17) obtained with a similar sol. The calculations show t h a t below p H 4.2 90% of the scandium is still in the form of Sc~+ The rest is mostly in the form of lower charged species ScOH 2+ in concentrations much too low to have any effect upon the coagulation of the silver bromide sol. At p H > 4.2 the concentration of Sc 3+ ion decreases whereas the concentration of all other species increases. -5.5

,

-0.5

7 -I.0

-4.0

o

io

m -% O Z

o z

-k5

h -4.5 0 0

-1-

o

(.~

-a.o

r~ -5.C .A O o

O .A -5.[

-6-0~. 0

o

6.0

5.0

-z.5

7.0

3.O

pH

FIG. 5. Circles represent the same critical coagu l a t i o n c o n c e n t r a t i o n s of s c a n d i u m n i t r a t e as given in Fig. 4. Squares give the ratio of the concentratioI~ of s c a n d i u m in the two hydrolyzed species of charge 4 + to the t o t a l c o n c e n t r a t i o n of scandium nitrate.

TABLE I I I C)~LCUL&TED

TOT2~L

CONGENTRATIONS

OF

4 ~-

~-IYDROLYZED S C A N D I U M S P E C I E S [Sc(N03 )~]to~

2.51 1.58 1.00 ~.30 3.98 3.16 2.80

X X X X X X X

pH

[Sc~(on)~ +] + [sc~(og)t +]

10-5 4.60 3.9 X 10-5 4.96 4.5 X 10-~ 5.29 3.7 X 10 -6 5.63 3.2 X 10-~ 5.97 2.5 X i0 -s 6.20 2.6 X 10-~ 6.40 2.7 X

10-7 10-7 10-7 10-7 10-7 10-7 10.7

y*

3.2 6.0 8.6 1.1 1.6 2.3 2.8

X X X X X X X

log 7

10-2 10-2 10-~ 10-1 10-1 10-1 10-1

--1.4c~ -1.22 -1.07 -0.9q

-0.7~ -0.64

*y = {2[Sc2(OH)~+] + 3[Sc3(OH)4+)}/ [Sc (NO~)Go~ The most important is the finding t h a t the concentrations of the two species of 4 + charge become significant in regard to coagulation and approach the c.c.e, for tetravalent counterions (16). Figure 5 gives the c.c.e, as a function of the p H (circles) along with a plot of the ratio of the sum of the concentrations of the two species of 4 + charge to the total scandium concentration (squares). I t is evident that the c.c.e, decreases as the concentration of the counterion of 4 + charge increases. This is in agreement with the Schulze-Hardy rule. Table I I I gives the total concentrations of the 4 + species as well as the ratio of the amount of scandium ion in the complexes of 4q- charge versus the total concentration of scandium ion along the c.e.c.-pH curve. The total concentration of the 4q- counterions is reasonably constant with an average value of 3.3 X 10-7M. This is somewhat lower t h a n the c.e.c, of 4-6 × 10 -7 which was determined for the simple T h 4+ with a similar sol (18). This constancy of the concentration would indicate t h a t the combined species of 4 + charge are primarily responsible for the coagulation of the sol. The lower charged species and the 5qcomplex are present in too low concentration to have individually any significant effect upon coagulation. The somewhat low e.c.c, of the q-4 counterions m a y be due to the combined effect of all other counterions. The concentrations in Tables I I and I I I are calculated using the hydrolysis constants for an ionic strength of 1.0. The total electrolyte concentration in the

JoUrnal of Colloid and Interface Science, Vol. 28, No. 1, S e p t e m b e r 1968

co

:Z o

o

%

TABLE

IV

6.0

5.6

5.2

2 . 0 X 10-5

4 . 0 X 10-5

10-4

10-4

10 -4

1.0 X

1.6 X

4.0 X

5.1

5.1

6.5

6.2

1.0 X 10-5

6.5

3 . 2 X 10-5

4 . 0 X 10-6

pH

[Sc(N0a)3]tog

10-7

10-7

10-s

10-s

7.9 X 10 -5

4 . 2 X 10-5

2 . 5 X 10 -5

5 . 0 X 10-6

9.8 X

3.6 X

8.8 X

7.2 X

[Sc~+]e

31.4

36.2

33.8

17.9

7.8

5.4

3.2

3.1

%

10-6

7.1 X 10-5

4 . 2 X 10 -6

3.1 X

1 . 5 X 10-5

7 . 6 X 10 -5

4 . 4 X 10 -6

2.1 X 10-6

1.8 X 10-6

[ScOH2+]

27.9

36.2

41.7

55.5

60.5

66.8

74.2

76.8

%

X

X 10-~

10 -5

10-0

10 -v

10-7

10 -s

10-6

6 . 0 )4 10 -~

2.1

1.2 X

2.9 X

7.0 X

2.3

5.1 X

3.8 X

[Sc2(0H)4+]

23.8

18.2

15.7

10.3

5.6

3.6

1.8

1.7

%

10 -7

10 -s

10-8

10 9

10 -9

8.7

X 10 -6

2 . 0 X 10-6

1.0 X 10-6

3.1 X

9.5 X

2.9 X

5.6 X

3.8 X

[Sc3(0}t)]+]

3.5

1.7

1.4

1.1

0.8

0.4

0.2

0.2

%

3 . 4 X 10 -6

8 . 8 X 10-5

5 . 6 X 10-5

4 . 2 X 10 -5

3 . 2 X 10 -6

1.6 X 106

10 7

),( 10-7 5.7 X

4.1

[Sc3(OH)~ ]

CALCULATED CONCENTRATIONS OF VARIOUS SCANI)IUM SPECIES IN SOLUTION ALONG TIIE STABILIZATION CURVE (SQUARES, I~'Ia. 4)

13.3

7.6

7.4

15.2

25.4

23.7

20:7

17.7

%

~D

0

d~ ©

O

©

©

©

H

©

C~ 0

18

MATIJEVI~, LEVIT, AND JANAUER

investigated coagulation systems was considerably lower. This should have some effect upon the calculated composition of the solution and may account for the fluctuations of data in Table I I I as well as for the slightly lowered c.e.e, for the 4 + scandium eounterions. Table IV gives the concentrations of all scandium species calculated for the points along the stabilization curve on Fig. 4. I t was established that the restabilization of lyophobic sols b y metal ions is due to adsorption of hydrolyzed species only and that the charge of the counterion has little effect upon its adsorbability (10). It was also shown that the slope of the stabilization boundary as plotted in Fig. 4 can be interpreted in terms of the metal ion to hydroxyl ratio of the adsorbed hydrolyzed complex (5). Between a p H of 5.2 and 6.2 the slope of the best line is - 1 , this would correspond to the ratio Sc3+/OH - = 1/1. I t is interesting to note that the two predominant species over this p H range are indeed ScOH 2+ + Sc2(OH)~+ which both have the required ligand ratio. Some deviation from this slope would be expected owing to the adsorption of species Sc3(OH)~+, which has a somewhat different Sc3+/OH - ratio. Simple calculation shows, however, that this deviation is within the experimental error of the data. It may be of interest to note that Yoshimura and Tateda (19) reported a strong adsorption of scandium ions from solutions on various adsorbents, such as quartz, feldspar, calcite, kaolinite, hydrous oxides, and oxides when the p H was kept between 6 and 8. It would then seem that the adsorption of hydrolyzed scandium species takes place on a variety of colloidal systems and not only on the silver bromide sol. This work shows that the coagulation and the reversal of charge effects of a hydrolyzable metal ion can be correlated with the composition of the electrolyte solution if sufficient information is available to determine the latter. It is obvious that it becomes impossible to detect the composition of an electrolyte solution from stability phenomena if the hydrolysis produces several species which coexist at a given p H in an electrolyte solution of a given concentration.

If only one hydrolyzed species is predominant its detection from coagulation and reversal of charge effects is quite feasible. ACKNOWLEDGMENT The authors wish to acknowledge the assistance of Mr. Paul Weisshaar, who carried out some of the preliminary experiments, and of Dr. Stanka Kratohvil, who determined the electrophoretic mobilities. REFERENCES I. KRATOHVIL, S., AND MATIJEVI~, E., J. Colloid and Interface Sci. 24, 47 (1967). 2. MATIJEVI~, E., MATHAI, K G., OTTEWlLL, R. H., AND KERKER, M., J. Phys. Chem.

65,826 (1961). 3. MATIJEVIC,E., AND STRYKER,L. J., J. Colloid and Interface Sci. 9.2, 68 (1966). 4. MATIffEVIC, E., ANn KERKER, M., J. Phys. Chem. 62, 1273 (1958). 5. MATIJEVI~,E., JANAUER, G. E., AND KERKER, M., J. Colloid Sei. 19,333 (1964). 6. LATIMER,W. M., "The Oxidation States of the

Elements and Their Potentials in Aqueous Solutions." Prentice-Hall, New York, 1952. 7. KOVALENKO,P. N,, AND BAGDASAROV,K. N., Peredovye Metody Khim. Tekhnol. i Kontrolya Proizv. Sb., 1964, 154-62. 8. STI~RBA-BoHM, J. S., AND MELICItAR, M., Collection Czech. Chem. Commun. 7, 131

(1935). 9. IVANOV-EMIN, B. N., AND OSTROUMOV, E. A., Zh. Obshchestva Khim. 14,772 (1944). 10. MATIJEVIC,E., KRA'rOttVIL, S., AND STRYKER, L. J., Discussions Faraday Soc. 42, 187

(1966). 11. KILPATRICK,M., AND POKRAS, L., J. Electrochem. Soc. 100, 85 (1953); ibid. 1Ol, 39 (1954). 12. BIEDERMANN, G., KILPATRICK, M., POKRAS, L., AND SILLEN, L. G., Acta Chem. Scan&

1O, 1327 (1956). 13. FROMAGE, T., AND FAUCHERRE, J., Compt. Rend. 259, 3274 (1964). 14. AVESTON, J., J. Chem. Soc. A 1966, 1599. 15. SCH-WEITZER, G. K., AND WINKLE'g, D. C.,

Proc. Intern. Conf. on Solvent Extraction Chem., GSteborg, Sweden, 1966, pp. 40-45. 16. MATIJEVI(~,E., SCltULZ,K. F., AND TE~AK, B., Croat. Chem. Acta 28, 81 (1956). 17. TEZAK,B., MATIJEVI~, E., AND SCHULZ, K. F., J. Phys. Chem. 59,769 (1955). 18. MATIJEVId, E., ABRA~SON, M. B., ScncI~Z, K. F., AND KERKER, M., J. Phys. Chem. 64,

1157 (1960). 19. YOSHIMURA, J., AND TATEDA, A., J. Chem. Soc. Japan, Pure Chem. Sect. 83, 1018 (1962).

Journal of Colloid and Interface Science, Vol. 28, No. 1, September1968