Diffusion Coefficient of Sodium Sulphate in AqueousSolution at 45°

M. L. Soon*, G. KAUR & S. L. CHOPRA

Department of Chemistry, Punjab Agricultural University,Ludhiana 141004

Received 21 August 1978; revised 7 February 1979; accepted21 February 1979

The differential diffusion coefficients of sodium sulphatehave been determined by the diaphragm cell technique at 45°in the concentration range 0.01-0.1 M. At these moderateconcentrations, the results are not in accord with the Onsager-Fuoss theory.

THE diffusion coefficients of potassiumv", magne-sium" and beryllium sulphates" have been

determined in aqueous solutions with the help of amodified diaphragm cell having a completely newdrive system devised in this Iaboratory+". The diffe-rential diffusion coefficients of sodium sulphate inthe concentration range O.OI-O.lM have beendetermined and the data reported in this note.

In this investigation the use of the modified formof diffusion cell" having a new drive system introducedin this laboratory+ was used. The iron sealed strirrers?were provided to remove the stagnant layer of theliquid adhering to the surface of the diaphragm. Astirring rate of 56 r.p.m. was used throughout theexperiments. The conductance of the solution in theupper compartment was measured at regular intervalsof time by conductivity bridge (Yellow Spring Instru-ment Co., Ohio, USA, Model 31). The high vacuumstopcocks were all spring loaded. The volume of thepores of the diaphragm cell was determined assuggested elsewhere", After filling the diffusion cellas suggested by Sanni and Hutchison", thediffusion process was allowed to take place forone to three days until steady state condition wasreached. Integral values of diffusion coefficients werethen evaluated with the help of Eq. (1)

- L,C,-D~ = 2.303 log L,C

o•• (1)

where D, ~, t, t:,.C, and L,Co are the integral diffusioncoefficient, cell constant, time (in seconds), final andinitial concentrations of the solutions in the twocompartments, respectively. The cell constant wasdetermined in the usual manners and the value ob-tained was 0.1603. The constancy of the cell constantwas checked twice during the present investigation.The integral values of diffusion coefficients obtainedfrom Eq. (1) were next converted into the morefundamental D values using Eq. (2)9

DO( ') D- (1 c.: ) c.: {DO( It}em = - Cm' + c;;:- em .. (2)

where

and Cm" .. (3)

and

,(

NOTES

D=DO+4c dIf .. (4)2 d 4c

Plots of 15vs 4"c, DO(em') vs 4Cm' , and DOvs 4(;are shown in Figs. 1, 2 and 3 respectivey.

The theory of Onsager and Fuoss'? leads to theequation

D=1000.RT(YI + yJ ( ~ ) (1+Co1n; ±) .. (5)

where Yl and Y2 are the number of ions that dissociatein the solution, m is the function given by (Eq.6)

° 0m = 1.0741 X 10-20 Al A2C °YI I z, I 1\

+ ~ in' + L, Iii" .. (6)where

l::,.m' =

.. (7)

f ,. •."~ •x 1-1010

l{lOO0·1 0·2 0·3 0·4./C-

Fig. I-Plot of Jj versus ve for Na2SO, at 45° [S.D. alongX-axis = 0.0033; and along Y-axis 0.005 X 10-1].

•r: •E •~1'10

/"01.0

0 ()'1 0·2 0·3 0'4JCm'-

Fig. 2 - Plot of D"" versus V Cm' for Na2SO, at 45° [S.D.same as in Fig. 1]

•

...,5?x o·-~ 04

,°0 0·2

o 0., 0"2 0·3 0~4

JC-Fig. 3 - Plot of !)OCm versus "-.\I C fOr NaaSO, at 45° [Slope =

0.72 X 10-6]

181

"

INDIAN J. CHEM. VOL. 18A, AUGUST 1979

and

rsm' (I Z2 IA~ZI I '\2 r .9.304 x 10-13

'tJo (€ T)2 c.1> (k a) .. (8)

The activity term ( 1 + C ~~2±) is repre-

d b (1 + C olny±) =1- 1.1514 '8(I)4"c

sente Y oC (1 + A' ~ C)2+ 2.303 BC -CIji(d) .. (9)

In these equations, D is the diffusion coe~cient(am 2 sec=), T is the absolute teII?-peratur~,.C IS theconcentration (moles per litre), y± IS thea~tIVlty c?effi-cient on the molar concentration scale, € IS the dielec-tric constant of the water, and 'tJ, its viscosity: Theequivalent conductances of the cation and amon areA~and ,\;, respectively, and N is their sum. a(l> is thelimiting slope of the Debye and Huckel theory.A'4"e = A 4"-; in which -eis the ional concentration,k is the reciprocal radius,. a the mean distance ofapproach of the ions, and A = 35.56 >:< ~ (~T)-I/2.The quantity 1> (ka) is. the exponential. integralfunction of the theory which may be obtained fromtables given by Harned and Owen!'. B is an empiricalconstant and C t/I (d) the term required to convertthe expression from rational into molar activitycoefficient and is given by Eq. (10).

(Od/oc + 0.001 ('YM1_M2)

d + O.OOIC ('YM1_M2).. (10)Iji (d) =

whered = 0.9957 + 0.0479c - 0.0023 C3/2 and M, and

M2 are the molecular weights of the solvent andsolute respectively.

The limiting value of the diffusion coefficient Dowas obtained from Eq. (11).

o 0

Do = 8.936 X 10-10 T 'Yl t;2 Al ~2 .. (11)'YI 1 I r;

In Table 1the specific quantities used in the theoreticalcalculations are listed. Substitution of these data inEqs. (5)-(9) leads to the numerical expression (12).

D = 7.934 X 1013 ( 1 + C o~~± )

(24.20 X 10-20 + 62' + 6~"-) ..(12)

where

TABLE 1- QUANTITIES USED IN THEORETICAL CALCULATIONS

318.160

73.73T A,

~(r> 1.835 0

116.00A.1'10 5.98 x 10-3 a(=r1+ra"') 2.46€ 71.70 B 5.279 x 10-5

""1 and 1". are the crystallographic radii

182

/

I

190

l70 '- n-l.nRnlr:AI

~t l50 •"'0

EXPERIMENTALxo no

1·10

1· 0o.!:-'-.-;!,o 2:-'--:' O~t.-'-·-::06:-'-'O:':8:-'--:-~':-O -'

Cone. c-Fig. 4 - Plot of D versus C for Na2SO. at 450 [S.D. along

X-axis = 0.001; and along Y-axis = om x 10·6j

TABLE 2 - CALCULATED AND OBSERVED DIFFUSION COEFFICIENTSor SODIUM SULPHATE AT 450

Conc. 106 D 106 Doba. 105 DCale. 10· D'(C) em2/see. cmvsec, ems/sec. ems/sec.M

0.000 (1.923) (1.531)0.01 1.195 1.234 1.709 1.4480.02 1.324 1.376 1.647 1.16530.03 1.142 1.207 1.603 1.5270.04 1.420 1.523 1.599 2.8590.05 1.045 1.131 1.579 2.8590.06 1.082 1.175 1.568 1.5290.07 1.080 1.177 1.553 1.5470.08 1.127 1.232 1.563 1.5920.09 1.050 1.163 1.546 1.5400.10 1.225 1.339 1.538 1.725

-6~ .rC=0.4478 X 10-20 'Y (13)C (1 + 1.295.f C) ..

6~" = 140.3 X 10-20 C. rP (k a) .. (14)

and

(1 + C olny± ) = 1- 2.113-iC_OC (1 + 1.2954"C)2

+2.303BC-C~(d) .. (15)

Comparisons of the experimental results with thosecomputed using Eqs. (12)-(15) are given in Table 2.In the last column values of D'[ = DObs+(D-Do)~alc]are recorded. The mean value of D'(1.531) is notequal to the limiting value Do. This confirmation ofthe inadequacy of the theory at concentrations up to0.1 M is in accord with similar agreement found forpotassium=>, magnesium and beryllium sulphates".The variation in the diffusion coefficients may beattributed to surface effects (below 0.05M) as sugges-ted by Stocks?" in addition to the effect of changingdielectric constant, changing viscosity of the mediumand hydration etc. In Fig. 4, the observed and cal-culated diffusion coefficients have been plotted againstthe concentration. It is to be noted that the experi-mental values of diffusion coefficient of sodium sul-phate are, however, obtained by the method of graphical integration as suggested by Stokes?". The devia-tions between the experimental and calculated resultscan however, be narrowed by the use of a new corre-lation suggested earlier--.

\

References1. Soon, M. L. & CHOPRA,S. L., Pak J. Sri. Res., 29 (1977), 7.2. KAUR, G., M. Sc. Thesis. Punjab Agricultural University,

• Ludhiana, (1974).3. Soon, M. L. & CHOPRA,S.L., Paper presented at the Annual

Convention of Chemists, Jaipur (1977).4. Sooo, M. L. & CHOPRA,S. L., Indian J. Tech., 13 (1975),

329.5. Soon, M. L., Pak J. Sci. Res., (Accepted).6. SANNI,S. A. & HUTCHISON,H. P., J. scient, Instrum., Part-Il

(1968), 1101.7. STOKES,R. H., J. Am. chem. Soc., 73 (1951), 3527. )Jp

8. Soon, M. L. & CHOPRA, S. L., J. Indian Chern. Soc., ..,2(1975), 98.

9. STOKES,R. H., J. Am. chem. Soc., 72 (1950), 763.10. ONSAGER,L. & Fuoss, R. M., J. phys. chem., 34 (1932).11. H.I,RNllO,H. S. & OWEN, B. B., The Physical chemistry of

electrolvte solutions,' (Reinhold, New York), 1957, 181.12. Soon, M. L., Acta ciencia Indica., 2 (1976), 110.

Metal Terphthalates & Dithioterphthalates & TheirComplexes with Ethylenediamine

C. L. SHARMA*,T. K. DE & A. K. SINGHDepartment of Chemistry, University of Roorkee.

Roorkee 247 672

Received 28 October 1978; accepted 6 March 1979

Amperometric and conductometric titrations of terphthalicand dithioterphthalic acids with Cu(ll), Ni(ll) and Co(ll) chlo-rides indicate the formation of 1:1 complexes, which have alsobeen isolated in the solid form and characterised on the basis ofanalytical and IR data. The interaction of these compounds withethylenediamine in benzene gives [Cu(en)2Jt and [M(en)31t whereM = Co(JO or Ni(lI) and t = terphthalate or dithioterphtha-late. The thermal studies on metal terphthalates and dithioter-phthalates have also been wade.

METAL terphthalates have been studied inrelation to their preparation by metathesis-".

The magnetic studies" of only copper complexes ofaliphatic and aromatic dicarboxylic (ortho substi-tuted) acids are reported in the literature. Thepresent note deals with the determination of compo-sition and structure of Cu(II) , Ni(II) and Co(II)

NOTES

complexes of terphthalic and dithioterphthalic acidsusing amperometric, conductometric, magnetic andIR studies. The results arrived at have been con-firmed by chemical analysis, DTA, TG and DTG.The interaction of these compounds with ethylene-diamine has also been studied.

Metal chlorides, terphthalic acid, ethylenediamine(en), benzene and sodium hydroxide were all AR(BDH) reagents. Dithioterphthalic acid was obtainedfrom Evans Chemetics, USA. The solutions of acidswere prepared in two equivalents of alkali and ofothers in doubly distilled water.

The solid complexes were prepared by adding equalvolumes of O.lM of the reactants. The heavyprecipitates formed were filtered, washed severaltimes with distilled water and then dried in a desic-cator over anhydrous sulphuric acid.

These compounds were treated with more than twoequivalents of ethylenediamine in benzene and themixture reftuxed for 1 hr. The resulting complexeswere filtered, washed several times with benzene an jfinally with absolute ethyl alcohol and then driedat ,....800 in an oven The insolubility oft he com-plexes in water and organic solvents precluded tnemolar conductance and molecular weight determi-nations

The amperometric titrations carried out at -1.6,-1.8 and -0.6V in the case of Cu (II), Ni(eI) andCo(II) respectively indicated the formation of 1:1complexes. This stoichiometry was also confirmedby conductometric titrations and chemical analysisof the isolated products (Table 1).

The ethylenediamine complexes are stable in solidstate or in organic solvents but dissociate in watergiving parent acids. The electronic spectra of theethylenediamine complexes were found to be thesame, indicating the formation of [Cu(en)2F+ or[M(en)3]2+where M = Co(II) or Ni(lI) , in solutionand the acids in the form of precipitates.

The IR spectra (vrnax in em-I) of metal terphtha-lates and of the acids indicated shift of v C=O,v C-O and v C-O + v O-C = 0 bands ofthe ligand appearing at /"oJ 1660, /"oJ 1410 and /"oJ 1270to 1570, 1380 and 1140 respectively in the complexes;

TABLE 1 - ANALYTICALDATA AND MAGNETIC MOMENTSOF THE COMPLEXES

Reqd.(%) Found(%) !l-eUComplexes (B.M.)

M C H M C H

[Cu (A)]a- 3H2O 24.96 37.71 2.73 24.81 37.35 2.71 1.54[Ni (A)] . 1.5H2O 23.51 38.44 2.80 23.45 38.38 2.78 2.82[Co (A)] . 2H2O 22.46 37.07 3.08 22.30 36.69 3.05 4.26[Cu (ens]A 18.28 41.43 5.75 18.20 41.06 5.71 1.89[Ni (en.IA 14.58 41.70 6.95 14.50 41.35 6.90 2.85[Co (en3)]A ·14.62 41.69 6.94 14.80 41.29 6.90 4.20[Cu(B)]2·12H20 17.28 26.11 4.35 17.20 25.89 4.31 1.45[NI(B)] . 3H.O 19.00 31.09 3.23 18.91 30.78 3.21 2.89[Co (B)] . 4H2O 18.02 29.36 3.67 18.18 29.08 3.63 4.28(Cu(en).]B 16.74 37.94 5.26 16.56 37.55 5.22 1.93[Ni (en).]B 13.50 38.64 6.44 13.38 38.38 6.37 2.84[Co (en).IB 13.55 38.62 6.43 13.77 38.24 6.36 4.24

en = CaHaN.; (A) = C.H,O, (terphthalate); and (B) = CSH.02S. (dithioterphthalate)

I

(

183