TitleEffect of pressure on the dissociation of electrolytic solution : I.Electrical conductivity of hexammine cobalt(III) : chloride athigh pressures

Author(s) Shimizu, Kiyoshi; Takizawa, Hideto; Osugi, Jiro

Citation The Review of Physical Chemistry of Japan (1963), 33(1): 1-5

Issue Date 1963-10-28

URL http://hdl.handle.net/2433/46830

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

The Review of Physical Chemistry of Japan Vol. 33 No. 1 (1963)

cv, ~.OF

THE R£VISW OF PHYSICAL CHE64ISFAY 01. JwFA.w, VoL. 33, No. I, 1963

PRESSURE. ON THE DISSOCIATION OF ELECTROLYTIC

I. Electrical Conductivity of Hexammine Cobalt (III)

Chloride at High Pressures

BY 1lIYOSHI SHIMIZII, HIDETO TAxIZAWA AND ]IRO OSUGI

SOLUTION

From the equivalent conductivity, .I;oF dilute solution (1.Ox 10-<-,-1.Ox 10-3.~~ of [Ca(\Ha)s]Claat 23'C under high pressure up to 600kg/cm~, the degree of dis-sociation. a. and the dissociation constant, K, of _[Co(NHa)s]CI%' farmed between

[Co(vHs)s]3' and CI- Lace been determined. d increases with increasing pressure. n end K have the minimum values at about 400 kg/cm~ and the volume change, VV, caused by dissociation, are l7 tms/mole at 300 kg/cm'- and -13 cma/mole at 500 kg/cm2. The equivalent conductivity at infinite dilution, da, increases from 183.3 to 189.0 under pressure. This may be due to the increase of the ionic mobility which is related with [be viscosity of water. The increase of A, there-for4 may be mainly ascribed to the increase of ionic mobility under pressure.

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Introduction

It. was shown by Hamann and Strausstl [hat the. ionization of-the simple electrolvtes were

enhanced at high pressures. From [he equivalent conduc[iciEes, d, of the dilute solutions under

high pressures, the variations of the degree of dissociation, a, the dissociation constant, K, and

the equivalent conductivity at infinite dilution, do, are determined, and aLo it is possible to

estimate the amount of the volume change, dF, due to [he dissociation o[ the electrolytes. The

authors have studied the ionic conductivity of the water solution of a complex, [Co(NH;~e]Cl„

at 25'C up to 600 kgJcm~ and examined the pressure edezr on a, K and do.

Experimentals

Hexammi¢e cobalt (III) chloride, (Co(NH,),;jCl„ was prepared from the water solution of robaltous chloride, ammonia, ammonium .chloride, and decolorizing charcoal as a catalyst by the

method of .Bjerrum and McReynolds2>. The crystals ware thoroughly washed with conductivity a~a[er and absolute alcohol, then dried to a constant weight at g0~100`C.

:1s show¢ in Fig. 1, the. conductivity cell made of te(lon, of capacity 25 ml and cell constant

0:322cm s, igas mou¢ted i¢ a high pressure vessel cortaining a thermocouple of chromef-alumel

as in the-previous papera). The solution, which was isolated with mercury in a glass cup from

(Received Augusl 1, 7963) I) S. D. Hamann and lV.$[rauss, Trans. Furadey Soc.; a`l, 1684 (1955)

1) w. C. Fernelius, lnorgonic Syntheses. II, p. 276 (1915) 11cGraw-Hill 3) &. Shimizu, Tlris lourrcel, 30, 73 (1960)

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i

K. 56imizu.

T G=G

asilicone oil, was compressed-by an of

Bourdon-type gauge. The pressure ves

The conductivity was measured at a t

cen[ra[ions of solution 1.0x10''•-1.Ox

of solutions under high pressures, it is

are available for the hexammine cobal

made in terms of thecompressibility

Resu

The equivalent conductivity, A, i

the equivalent conductivity is proporC

effects of pressure on the ionic mobilit

Fig. 3 shows the p1oLS of the equ

concentration, Ct/z, w•hic6 follows Foh

curves lie slightly below Onsager's the

ion-pair [Co(NH~,JCIz+ formed beta

Linhard and ilfonks>. Then, the ion-pai

and CI-:

[Co(NH,)e (1-a)n

where a is the degree of dissociation a

4) R. E, Cibson and 0: H. LoeRle 5) V. Jl. Linhard, Z. FJekfrochene.

I. L. Jenkins and C. D. Monk,

The Review of Physical Chemistry of Japan Vol. 33 N•

eu, H. Takizasvaand J.. Osugi ~ .

o -

Fig. t High pressure conductivity cell V :high pressure vessel

M : mercun-C 5 : solution C : tedon cell

S O: silicone oil G

G :glass Cup ~~ M T

c thermocouple

V

I injecto-. The pressures were measured by a calibrated set was. immered in a temperature bath of liquid paraffin. emperature 2i-C, at pressures 1600 kg/cmr and at con-

10-s .V. Tn order to calculate the equivalent conductivity

necessary to know [heir compressibility. No such data

t (III) chloride solutions and thus the calculations were

of water+l.

Its and Considerations

ncreases with increasing pressure as shown in Fig. 2. As tonal to ionic mobility a¢d the degree of ionization, the

y and degree of ionization should be examined. ivalent conductivity. ,1, against square root of equivalent

Lrausch~s empirical low. The experimental conductivity

oretical lines. This slight difference may be attributed to ~een [Co(NH~s]'* ion and CI- ion as pointed out by r [Co(NHa)fi]CF* would be in equilibrium with [Co(NHa)„]'*

]Clr* ̂ [Co(NHs)a]s* + Cl' r am (2+a)m

nd m is molar concentration. The equivalent conductivity

r. !. dm. Clrem. Soc., 63, 893 (1941) 59, 114 (1944) 1, Ckem. Soc., 19al, 68

w.

~;.

;.

~~-.^.

6

Effect of Pressure

The Review of Physical Chemistry of Japan Vol. 33 No. 1

on tLe Dissociation of Electrolytic Solution 3

(1963)

S ~

>so

<,~

12

'-~`

rre~ ' I Q~ o, ~ ~ ~ ° >m ~ a~

Fig..2 Pressure dependence of equivalent Fig. 3 Equivalent conductivity of ~ conductivity of [Co(NHs)s]Clr [Co(NH3~]Cls at two pres-

-~-: 1.Ox10-aN -0-~ lkg/cm2 -~-: 600 kg/cm2.

---: Onsager's theoretical line

is as follows,

r

where w is the solvent-corrected specific conductivity, Zs [he ion valency of ith ion, me the

concentration (g ion/1) and do the ionic conductivity.

Then,

dC= 3zXmO.[Co(VHa)a73' ~' SCI-) t 2(1-IX)m(.[[Co:\Ha)a7C1'*'i z1C1-)-

.. d=cYA"+ 3 [1-cr)ifz`=al\AOS,_ 3 ~ zr\_lbsr._ 3 bzt111M-y 2 (

where

~fCo~NH°)e]s* + aCl-= nsi = A0u _ bul`/2.~

Alcufi`Ha)e1cP• + .tcl- = Az1 = ~ z` - bz`I vz

and ionic strength, 1, is,equal to C(1+~).

In [his case, the ignic mobility of thebivalent ion-pair is taken as two-thirds of that of the

tervalent cation. Thedegree of dissociation,. a, is obtained from Fy. .(I) and the experimental values of d under pressures by means of successive approximation.

The dissociation constant, K, is represented by the following equation.

K={[CO(i\rH°)°}'*}.{Cl-}_~(2+a)mjjz (2)

where fr (1, 2, 3) are the activity coefficients of [Co(NH~°]'•, CI- and [Co(NH;)s]CIZ'. which

have been calculated from the Debye-Huckel equation,

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eTh Review of Physical Chemistry of Japan Vol. 33 No. 1 (~ i

•~

4 K. Shimizu, H. aT kizawa and J. Osugi ~. •

-)ogf, 0.509 Ztz71/2:f

ca;~ .~The results are shown in Table 1, Figs. 4 and 3. As shown in figures, the degree ~

ra~.:

Table 1 A, a and /i under pressures .~

PIx IO-~:V 2x10-~N 3x 10"4N !:

(,kg/cm2) Aan x•lo3 a a F•lW A a K•107: ~3 •

1 183.3 179.5 0.9929 13 177.9 0.9896 1 i 176.fi 0.9859 18100 185.8 181.3 9.9859 6.3 l i9.i 0.9789 8.0 178.2 0.9754 t0

200 186.9 182.3 0.983fi 3.fi 180.4 0.9 i67 73 I i9.0 0.9119 8.7300 188.0 183.2 0.9813 4.8 18].3 0.9743 6.fi 179.8 0.9683 7.7 !~400 188.7 183.9 0.9813 4.7 181,9 0.9 131 fi.3 180.3 0.9660 7.2

3W

6~

189.0

189.0

184.2

184.3

0.9613

0.9823

a.e

s. ~

182.3

182.3

0.9741

0.9140

6.6

6.6

180.8

180.9

0.9683

0.9691

7.8

8.1

P (kg/cmZ) A

5 x 10-+N

K K• 10~ A

8xt0-+1'

n K•10~

10 x 10'~ N

A a K•IW

goo

zoo

300

400

500

600

174.7

175,8

176.7

177.3

177.8

V 8.4

178.7

0.9823

0,9654

0.9629

0.9570

0.9546.

0.9581

0.9617

21

IC

10

8.9

8.4

9.0 10

nz.a

173.3

174.1

154.6

171.0

175.1

175.8

0.9768

0:9572

0.9533

0.9462

0.9426 0.9449

0.9483

26

13

l2

ll

]0

ll

11

171.2

171.9

1)2,fi

173.0

173.5

113:9

174.4

0.9749 0.9527 0.9477 0.9390 0.9367 0.9376 0.9435

28

IS

13

ll

11

I1

I2

i QM

ass

OW

e

DD

O

0

Fig. 4 Pressure dependence of degree of dissociation of [Ca(\H~)sJCh

-Q-: 1.0 x 10-~ N -~-; 2.0 rr

-~-: 3.0 n '~: 5.0 n -(}-: 8.0 n -~-: 10.0 0

Presave. k¢~'cm'

sociation

kg Jcma.

according

of each solution and the

The pressure coefficient

to the thermodynamical

dissociation constaet have

of In K gives. the volume

relation as Follows,

the minimum values at

change, dV, due to the

about 400

dissociation

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Effect of Pressure

The Review of Physical Chemistry of Japan Vol. 33 No. 1

on the Dissociation of Electrolytic Solution 5

loo

:~

~~ Fig. 5 Pressure dependence of -:~ log lie/Xt of [Cd~rk7Clo

. ieo

oe aw .oo sm Pressure, ka/vn'

r71nKl _dV ~4) 8P /r RT'

dV are l7 cm'/mole at 300kg/cmo and -13cm~/mole a[ SOOkg/cm2, the sign of d1' changing

from positive to negative at about 400 kg/cmz. dV may be equal to dVt+dVr. dVr is the

volume change of ions themselves and positive in this system. dV, is the volume change of

sohent attracted by ions under pressures and negative because of [heincrease of ionic valencies:

dVt would be predominant at lower pressure so that dV is positive. At higher pressure, dT',

would take place of dV„ for wateq of which the dielectric constant increases with increasing

pressures, would 6e attracted much more by ions. Then pressure would favour the dissociation of ion-pair to ration and chloride ion.

~.m

~,.w

Fig. 6 Pressure dependence of equivalent conductivity at infinite dilution of [Co(NHa)s]Cla and viscosit}' of water

-~-: >I°/yr at 23'C (Cohen) -~-: i at 30'C (Bridgmanj

osso wo ~

Pressure. kg'an'

The equivalent conductivity at the infinite dilution, At, increases from 183.3 to 189.0 with

increasing pressure as shown in Table L This may be due to the increase of the ionic mobility,

which is related with the viscosity of water. rl. The variation of d, and p by pressure hate

similar tendencies as shown in Fig. 6. although R'alden's rule is not best obeyed by this electrolyte.

The increase of ~ by pressure, therefore, may be mainly ascribed to the increase of ionic mobility.

The authors have great pleasure in expressing their sincere thanks to the Department of

Education [or the Granb in Aid for Fundamental Scientific Research.

The Laboratory of Physical Chemistry

Kyoto University

Kyoto, Japan

6) B. K. P. Scaifc, Pror. phys. Sor., BfiB, i90 (1955)

(1963) i

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