Indian Journal of Chemistry Vol. 4 1 A. Deccmber 2002. pp. 2462-2467

Study on tran sport behaviour of Bi(N03)3 in water + DMF/DMSO

J Ishwara Bhat * & TN Sreelatha+

"' Department o f Chem istry . Mangalore Uni vcrsity. Mangalagangothri 574 199. India

E-mail: bhalij @yahoo.com

+ Department o f Chemistry. S N Co llege. K:lI1nur ()70 007 , India

Receil 'ed 6 Jllll e 2001 : rel'ised 29 Aliglist 2002

l1i smuth nitrate is subjected to electri cal conducti vity stud ics in water + DMF and wa ter + DMSO at fOUl' different temperat ures, Limi ting molar conductance of 13 i(NO,), has been dctcrm incd at all compositi ons of DMF and DMSO w ith \Va ter and at diffcrent tempcratures , Limiting conductance is found to be less in wa ter + DM F mi xture th an in wa tcr + DMSO mi xturc. Large value o f lim iti ng con ductance is interpreted duc to the relcase of proton from the co-solvent on account o f thc acti on o f Lew is acid (13i '+) on DMF or DMSO in thc prcsence o f water, Di ssoc iati on and assoc iat ion constant s ha ve been calcul ated. Exothermic nature of tile sys tem is supported by the va lues o f thennody nailli cs of assoc iation as we ll as solvat ion. Prcfcrelllial so lvat ion o f the cati on by the non-aqueous solvent has bccn obse rved. So lvati on number of the spec ies has be(:n cai culated and found to be fractiona l indi ca ting the formati on o f sDlven t scparated ion-pair i n thc system L1ncler cx isting condit ions.

T he chemi stry of bi smuth is di verse, but is perhaps the best es tabli shed of the heav ier stabl e elemen tsl

.

Complexes of bismuth typi ca lly have low solubi lity in most sol vents. The bio utility of bi smuth and its compounds have a 250 years history, which is described in a number of key rev iew articl es I., . After

extensive use in the trea tment of syphili s as well as other bacterial in fections, nevertheless, bi smuth compounds remain importan t components of stomach remedies". Inorgani c bi smuth sa lts were the first compounds to bc recog:i iscd for therapeutic utilit y. Kasanov} and others used bismuth in the preparati on of superconduct ing compounds, whcre as Li and othels' in their biotechnology works. Koiwa u ~ed it in thc study of ferro clec tr ic filmS. Chung(, studied the conducti v ity in the solid state. But there are no reports in l iterature about its conductivity or transport and so lva ti on behaviour in solutions except for two old works7.x. Thi s has warran ted us to take up the present concluctometri c or solvation studi es of various bi smuth compounds.

Materials and Methods Bi smuth nitrate (A R Grade, Sd Fine-Make) was

used as such , w ithout any further purifica tion. Tripl y di still ed water o f conducti v ity of the order of - I x I 0-6 ohm- I cm - I and puri fied non-aqueous solvents such as N,N c1imethy l formamide (DMF) and dimeth y lsulphox ide (DMSO)(conductivity of the oreler o f O.5- 1. 5x I0-7anci 2.0-3.0x I0-70hm- 1 cm- I)

were used in the entire work. Solu ti ons of Bi (NO,)y were prepared in non-aqueous solvent instead of water to avo id hydrolys is prob lem and required amoun t of water was then added to it, so as to get ca lculated % compos iti on of ,ther DMF or DMSO(v/v) .

Conductance measurements werL~ made w ith a digital direct reading conduct iv ity meter (model CM 180, Eli co make) and a ca li brated type conductivity ce ll . All the measurements were made In a thermostat/cryostat mai n tai ned at the dcsi red

temper;:~ture ±O.O I °C. The instrument ,vas standardi sed as described elsewhere'}

Results and Discussion Lillliting condllctance

Sol utions of bi smuth nitrate in di mcthy I formamide or dimethyl sul phoxide with the ca lcul ated amoun t of water were subjected to conductometric study. The specific conductance va lue so obtained (cell constant

of the ce ll was 0.999 cm- I, hence the instrumen t gave the specific conductance) was used in the determination of molar conductan ce (1\111)' At the initial stage, Debye-Huckel Onsager equation was used to evaluate the limiting conductance. But the plot

of 1\111 versus Vc was non- linear. Hence, Kraus- Bray equat ion related to 3: I elec trolyte was used, bu t the plot of (I\me)' versus II /\ n was also non -linear. Figure ( I ) A is a representative plot at 5% DMF/DMSO at 303K. So Mi shra et a/' s8 proposal of I : I nature of

BHAT el al.: TRANSPORT BEHAVIOUR OF Bi(N03h IN WATER+DMF/DMSO 2463

(Am·C)

2· 0 16 1·2 0·8 04

8

> 10 3

B x

12 0;

12

A

o 04 08 12 (6----ro ~------~~

(A m C)3

Fig. ( I )- A. Pl ot of 1/ A 111 (ohm cm- 1 11101) V s (Am c/ (mho/cm)' for Bi(N03), at 303K. t.. 5% DMF ; 0 5% DMSO. 13. Plot of 1/ A 111 (ohm cm- 2 mol) Vs (A I11 ' c) (mho/cm) for Bi(NO,), at 303K. t.. 5% DMF; 0 5% DMSO.

Bi(NO, )} was used. The Kraus-Bray eq uatio n for I : I e lec tro lyte may be represented as

• ? 0

1 I A 11/ = A 11/ c/ K c. A 11/ - + 1/ A II/ . .. (l)

where Am is the molar conductance, c is the concentration Kc is dissociation constant and (A olI/) is the molar conductance at infinite dilution or limiting molar conductance. The Kraus-Bray plot obtained for Bi(N03h in water + DMF or water + DMSO was linear (Fig. ( I) B is a representat ive plot). From the intercept and slope of the above linear pl ot the limiting conductance (A 'I1\) and the dissociation constant (Kc) were obtai ned and are shown respectively in Tables I and 2. These measurements were done at 288 , 303, 308 and 3 18 K and at different compositions of DMF and DMSO (5, 20, 40, 60, 80 and 100% DMF & DMSO). The data are shown in Table I . But thus obtained limiting conductance va lues are not abso lute as they do not account fo r the effect of io nic mobility and act ivity co-efricient on conductivity . Therefore, Shedlovsky mode l was tried,

. which accounts for the above fac ts and hence expected to give abso lute limiting conductance. The Shedlovsky eq uati on may be represented as ,

2 ' 2 • I ISAII/ = K". cAII/Sj ±I All/ + I I All/ ... (2)

where S is Onsager slope, K" is the aSSOCIation constant andj~ is the mean ionic activity coeffic ient of the e lcctrolyte.

From the intercept and the slope of the linear plot of 11SAII/ versus cAII/S/ ±> the limiting conductance and assoc iation constant (Ka) were determined. These values are shown in Tables I and 2.

From T able I , it is clear that temperature enhances the conductivity value at all compositions of water + DMF or water + DMSO. As expected, temperature increases the mobility of the species and increases the vibrat ional and translational motions of the species . So conductance continuous ly increases .

The limiting conductance decreased with increase in % co mpos ition of DMF as we ll as DMSO in water, till 100% DM F and 80% DMSO (w ith a late r increase till 100% DMSO). Since the so lution is not stable in water, no conductance data is avail ab le in water or at 0% DMF I DMSO. At 5% DMF I DMSO, the value is found to be very high. Similar unusual high value was also obtained by Viterbo et at.? in HN03 medium . They attributed it for the hydro lys is of the sa lt in water and due to the formation of HN03 in the so lutio n. In all compositions of water + DMF/DMSO. there ex ists solvent-solvent interact ion apart from ion­solvent interac ti on. The interactio n increases as the amount of DMF/DMSO increases in the mixture. Due to such interactio n, probab ly a large mixed solvent molecule wi ll be formed and it is in volved in the solvat ion of the species of Bi(N03h- Hence, size of the effecti ve conducting ions increases and conductivity decreases. Non-aqueous solvent DMF or DMSO increases the 3-dimensional struc ture of water, thereby forming cages or ho les. Holes thus formed capture the conducting spec ies and lead to decrease in conducti vity. Thi s process continues till 100% DMSO or DMF. Accordi ng to Paul el 0 /. ' 0 Bi(N03h, is a Lew is acid. [n the initial stage large amount of W may be released from wi.lrer+DMF/DMSO solvent mi xture and hence conductance is very large, due to Grothus type of conductance. This was one of the reasons attributed to high conductance of any Lewi s ac id in DMF' o. DMF or DMSO, being do nor molecul es, forms [Bi (so lven t) (N03ht N03-- . As the amount of co-solvent increases, the rate of formati o n of cavity also increases and re lease of H+ decreases. Due to all these conductance decreases. At 100%, anyway there is no solvent-so lvent interaction i.e, no water molecules to make Bi(N03h Lewis acid. Hence conductance decreased drastically. In the case of 80% DMSO, conductance is smaller than 100% DMSO. This is in accordance with the viscos ity data. Here, the viscos ity is found to be higher when compared to 100% DMSO or DMF or even 80% DMF.

2464 INDIAN J CHEM. SEC A, DECEMBER 2002

Tab lc I - Experimenta l molar conductance at infinitc dilution for l3i(NOJ») from different mode ls in vari ous so lvcnt compositions (v/v) of water + DMFI DMSO at

A"", ( mho cm2 mol- [)

watcr+ DMF

T (K ) :i'Yc- 20'Yc-· 40% 60% XO% 100%

2 2 I 2 2 I 2 2

288 746.26 746.26 462.96 462.96 273 273 169 169 110 11 0 106 III

3()] 952.38 952.38 609.08 60908 392 392 24 1 244 167 167 143 143

308 10000 1000.0 649.40 649.40 425 425 260 263 185 185 152 166

3 18 11 23.6 11 23.6 724.60 724.60 454 454 286 290 2 17 2 17 179 190

water + DMSO

303 11 90 1190 826 833 505 504 263 270 110 110 135 142

308 1265 1265 8S5 8S9 538 539 286 290 133 132 147 154

11:1 135 I 1351 l)52 957 57 1 573 323 328 145 147 159 167

l lX 1-1 28 1-I2X 1010 101 5 621 625 345 35 1 157 167 175 179

I -Kr.[us- l3ray modcl : 2-Shcd lovsky modc l.

Tab le 2- Expcrimcntal va lucs of Kc and K" fo r l3i (NOJ).l in various compositi ons (v/v) o f water + DMF and water + DMSO at di ffcrent tcmperatures

K(· K" watcr + DMF

T (K) 5% 20% 60'Jr SO% 100% 5% 20% 40% 60';\'0 80% 100% 40%

2SX 0.0 150 0.01 8 o.o:n 0.042 0.02') 0.002') m 5 1 32 23 .9 40.2 53 1 30] 0.0160 0022 0.026 0.()]8 0.0 1') 0.00 18 62 46 46 33.9 55.5 824 308 O.O I ')S 0.028 0.02-1 0.035 0.01 8 0.0016 52 3 1 4S 36.7 63.7 1102 3 18 0.0260 0.03-1 0.02 1 0.03-1 0.01 7 0.0014 43 24 49 37.8 64.7 1209

water + DMSO ] 0] 0.0090 0.014 0.011 0.0050 0.023 0.0 17 30X 0.0 110 0.015 0.01 3 0.0055 0.0 18 0.0 16 3 13 0.0120 0.0 16 0.01 4 0.0057 0.015 0.014 3 18 0.0 I SO 0.020 0.01 6 0.0069 0.01 3 0.0 12

Kc from Krau s - I3 ray modcl: K" from Shcd lovsky mock l.

Dissoci(l / iOIl/ossocio / iOIl CO li S/Oil/

Dissoc iat ion and assoc iati on co nstants were obta i ned from the slopes of respecti ve pl ots, namely, Kraus- Bray and Shed lovsky. These va l ues are shown in Table 2. From Tab le 2, it is evident that with the increase in temperature, the di ssoc iati on constant (Ke)

inc reases wh ile association constant (Ka) decreases. Th is indicates that increase in temperature fa vours the dissoc iation and the reaction seems to be exothermi c in nature. For water + DMSO, Kc vari es sinuso idally with the in crease in co-so lvent DMSO, whereas in waleI' + DMF, Ka decreases up to 60% and then there is increase till the end. The variati on in viscosity may be res ponsible for thi s observed fact. It might be due to the selec ti ve so lva ti on of cation by the co-solvent also. The selecti ve so lvati on of cation by the DMF or DMSO prevents the approach of anion near cation. This is supported I I by non-linearity obtained for the plot of log Ko versus 1 IE.

107 75 94 26 1 49.4 100.5 90 72 83 2 13 75 .7 106.5 85 63 67 207 90.4 11 2.0 76 56 64 175 98.0 124.0

Woldell prodllc /( ; (11/ 1]0)

Walden Product is the product' 2 of limiting conductance and viscos ity or the solve nt. The product is calculated at all temperatures and % compositions of water + DMF and water + DMSO. The variation of the product with calculated mole fract ion of DMF or DMSO is shown in Fig. 2 (A and B). In the case of water+DMF, the Walden product sl ightly increased in the beginning at all temperatures, except at 3 18K and then decreases ex ponenti a ll y at all temperatures fo r both the cases . Decrease in the product is an indication that the variati on in limi ting conductance is not compensated by the variation in viscosi ty. Moreover, it also shows that the Stoke ' s molecular radius increased with the decrease in di electri c constant or increase in % composition of co-solvent. Theoreti cally, Walden product is reciprocal to Stoke' s molecular radiu s and present ly calculated Stoke' s radius is on ex pected line (values not shown ). The

~.

BHAT el 01.: TRANSPORT BEHAVIOUR OF Bi (NO, ), IN WATE R+DMFIDM SO 2465

observed decrease of A'1ll 11 0 with the addition of DMF or DMSO can be explained in terms of selective solvation of cation by the co-solvent molecule in the mixture. The ex istence of maximum on Walden product can be explained on the basis of hydrophobic dehydration I] of cation due to the presence of co­solvent .

Th ennodyn.alllic parameters It is a well known fact that conduction of an ion

depends on the rate of movement of ions and wh ich in turn depends on temperature. That means, Arrhenius relation 1(11/ = II e - £a/ RT is appl icable here . On the basis of this, a plot of log 1(111 versus '/, was drawn and was found to be linear. From the slope of thi s plot, energy of activation (E,,) of the rate process is obtained. These values are show n in Table 3. The frequency factor A can be obtained from the intercept of the plot. E" is almost a constant till 20% DMF/DMSO, then increased to a large va lue till 80% and then decreased. Thermodynamic parameters of association such as t...Ha, t..Ga, & t..Sa were also

Mole fraction )·0

B

10

o 0-2 01, 06 08 ),0 M ole fracl ion

Fi g. (2)- Plot of ;\0", 11u (mho c IT1 ~mo l - 1 Poise) V, mole fraction for Bi(NO, ), . A H20 + DM F system : 0288 K; 303K; /':, 308K; X 3 18K. 13 H20 + DMSO system: 0303 K; 308 K; /':, 313K; X 3 ISK.

calculated. I1 Ha is obtained from the plot of log Ka

versus '/,., and t..Ga from the equati on: t..Ga = - RT In Ka. t..Ga was calculated at different temperatures and then an average va lue was obtained. I1Sa was obtained from usual ex pression. These values are shown in Table 3. t..Ha is found to be negative till 20% DMF, showing the exothermic behaviour of the system as proposed under di ssociation / association constant and then it became endothermi c. Both the behav iours are feasibl e, since t..Ga is negative. Even in the case of water + DMSO t.. Ha is negative till 60% and then is found to be pos iti ve. I1Sa is very small co mpared either with t.. Ha or t..Ga . The negative entropy states that the spec ies are stabl e in the presence of a solvent/solvent mixture. In water + DMF, th e system is exothermic, spontaneous and has negati ve entropy in the water rich region.

Thenl/orlYl/wl/ ics q/ solva t iOI/ Solvati on is a process where an ion gets covered by

the so lvent sheath . Usuall y, the solvent molecules present in primary layer is call ed so lvati on number. Thermodynamics related to thi s is ca ll ed thermodynamics of so lvation . Born equati ons 12 are used to compute the thermodynamics of solvation such as t..Gs .. ,·, t..S,.s and t..H, .s·

Corrected Stoke's radius of an ion in a so lvent was calcu lated usi ng Eq . (3),

r; = 0.82Z/ A() 110+ 0.0103 € +r,. . . . (3)

here r ,= 0.85 A describes dipolar unassociated solvents and r ,,= 1,13 A applies to protic and other associated solvents, The values of the corrected Stoke's radius are show n in Table 4, The corrected radius did not change with temperature, but sli ght decrease is found wi th increase in DMF content till 60% with a further increase till 100% of it. Computed values of thermodynamics of solvation are shown in Tab le 5, A plot of - AGI . , versus '/1'; is found to be linear indicating the system to follow Born equ ati on,

Table 3-Computcd thermody namic paramcters for Bi(N03h under va rious compositi ons (v/v) or water+DMF and wate r + DM SO

Thermodynamic 5% 20% 40% 60% SO% 100% parameters 2 2 2 I 2 I 2 2

Ea (kJ mol- I) 10.2 1 9.4 1 10. 14 9. 15 16, 23 9.46 15.95 13.56 16.750 20.94 13.55 II .S5

L'. Hoa(kJ mol- I) - 12.56 - 15.32 - 19. 15 - 12.63 13.2 - 20.27 15.20 -22.2 16.500 22.4 1 19.9 6.45

L'.Gua(kJ mol - I) - 10.15 - 11.58 - 9,08 - 10,82 - 9.58 - 11 .14 -8 .~n - 13.83 - 10.160 - 11 .29 - 17. 16 - 12. 13

L'.Soa( K- I kJ 11101- 1) - 0,008 0.012 - 0 .033 O.005S 0.075 0 ,029 0,079 0.027 0,088 0.108 1 0.0 12 0 .059

I. water + DMF mi xture; 2. water + DMSO mixlUre,

2466 IND IAN J CHEM, SEC A, DECEMBER 2002

Table 4-Corrected Stoke's radius in A of the spec ies of Bi (NOJ)J under varying compositi ons (v/v) of water+DMF and waler+DM SO at diffe rent temperatures

H20 + DMF T(K) 5% 20% 40% 60% 80% 100%

288 2.0589 1.9897 1.9 11 5 1.5657 1.6088 2.0765

303 1.9868 1.9406 1.8609 1.5267 1.5603 1.9730

308 2.0030 1.9348 1.8593 1.5440 1.5778 1.9706

3 18 2.0131 1.95 II 1.90 I 0 1.6 184 1.63 14 1.954 1

H20 +DMSO

303 2.0305 1.98 13 1.9704 1.9586 2.0 186 1.8lJ70

308 1.9545 1.974 1 1.965 1 1.9290 1.9947 1.8766

313 1.9320 1.9649 1.9530 1.9 170 1.9788 1.8440

3 18 1.894 1 1.9438 1.9-106 1.9097 1.9736 1.8 176

Tab le 5-Thcrmodynamics o r so lvali o ll ror 8 i(NO.d, in various cOlllposiliollS or wa lcr+ DMF and walcr + D,\;150 al difTc:rcll l Ic mpcralurcs

Walc r + DMF T(K) 5rhl 20% 40% 60% 80% 100%

2 :1 2 3 2 :1 2 3 2 3 2 3

2RS 325.X (l.O2-1 3E 336 0.025 3-1-1 3-1X.3 0.03 1 357.4 421.7 (W47 435 .2 407. 1 0.052 422 3 13 0.042 325

303 33.''>.3 0.0 .10 3-14 A 342 o .rn l 352 354 .9 0.039 366.6 427 .9 0 .058 445 .5 4 14 ') (1.064 434 :n6 0.05 1 34 1

.108 33K .4 0.010 3-1 1.5 343 oem 353 354.S 0.039 366.7 4 18.2 o.on 440.4 402.4 0.087 429 324 D.D55 34 1

3 18 339.3 O.OIU 339. 7 :nli (um 3-19 3-1-1 .6 0.0-1 3 358.3 393.6 0.08 1 4 19. 3 382.3 O. IOU -1 14 324 (l.()62 344

Waler+ DM50

303 3 15. 1 0.074 337.4 34 1. 2 0 .01 4 345.5 34 1.S 0.01 9

308 32 1.8 o.on 350.2 342 . 1 O.OI S 346.7 3-12.0 (l.020

3 13 :nS.7 (L()49 354. 1 340 .3 0 .025 348.2 340.8 (1.030

3 18 343.3 (LOSS 360.9 343.4 (Um 35 1.9 3-1 2. 1 o.(m

I. - L\H,.,( kJ mor'): 2. i\5,,(K- ' Umo l ' ); 3. - L\G,., (kJ 11101- ')

Solvatioll IIlIlIl b e r

An allempt is made to calculate the so lvati on number of the spec ies involved as fo llows. Effect of solvent on kinetics of reaction is well known . Hence, \.ve correlated the rate constant , k to the limiting conductance J\ 0 ", as done earl ier and tried to plot log J\ 0 ", aga inst / / t; on the basi s of the equat ion,

... (4)

Here Z;\,ZIl are rhe ion ic charge on the cation and anion, e is the electroni c charge, t; is the di electric co nstant, d f\li is the inter nucl ear di stance, k iJ is the Boltzmann constant, and T is the temperature on abso lute sca le. The plot of log A 0/1/ versus / /e (€ was obtained by varyi ng % co mposition of water + DMF/DMSO at a give n temperature) was linear at all temperatures . It gave a slope of Z;\ZB e

21dAB kbT, from whi ch the va lue of internuclear di stance d ;\11 is de termined. Internuclear di stance is smaller in water + DMSO, compared to water + DMF. This IS 111

accordance with the variation in J\ om (Table I) .

3-1 7.4

3-1 8.2

350 .2

352.3

342.7 0.02 1 349 .2 328.0 0.034 338 336.0 007 1 1,57

347.5 0.023 354 .5 330 .X (l.O37 342 336.9 0.078 36 1

348.4 (1.026 356.6 334.0 0.034 344 329.3 0.010 366

349. 1 0 .027 357.8 333.9 (U)36 3-15 3:.4 .7 0. 120 :17I

Corrected Stoke 's radius va lue obtained from Eq. (3 ) is made use of as fo llows. In the case of pure so lvents, the rad ius of so lvent molecule was taken from literature l

", . 15. In the case of solvent mi xture (water +DMF/DMSO) (it was assumed that solvent mixture form s spheri ca ll y shaped species) such radius was obtai ned as foll ows. If rl. r2 and r represent the radius of water, DMF/DM SO and the so lvent mi xture molecule (water +DMF/DMSO), then vo lume of the solvent mixture molecu le is gi ven by,

V=4/3 m/ +4/3 nr/ = 4/3 n(rl 3 + r/) .. . (5)

But V = 4/3nr' . .. (6)

where r is the radius of the solvent mixture molecule. On eq uating the R.H .S. of equations (5) and (6),

... (7)

If ri is the corrected Stoke's radius obtained fro m Eq. (3) and d AB, the internuclear distance obtained

BHAT et al.: TRANSPORT BEHAVIOUR OF Bi(N03h IN WATER+DMF/DMSO 2467

Table 6- Sovlation number of the cation of the species of Bi(N03h in water+DMF and water+DMSO at different temperature

Water + DMF T(K) 5% 20% 40% 60% 80% 100%

288 0.50 0.45 0.42 0.32 0.33 0.50

303 0.40 0.37 0.35 0.25 0.26 0.41

308 0.40 0.37 0.35 0.26 0.27 0.41

318 0.40 0.38 0.37 0.28 0.29 0.41

Water + DMSO

303 0.56 0.55 0.55

308 0.56 0.56 0.56

3 13 0.53 0.54 0.53

31 8 0.52 0.53 0.53

from Eq . (4), then, it is assumed that dAIJ - ri gives the radius of the total no. of left over solvent molecules.

Then, dAB-ril r sol/soLmi . is calculated, which corresponds to the number of ~olvent molecules surrounding a particular ion, which is the solvation number. The solvation number obtained in the present case is fractional and are shown in Table 6. That means, single solvent molecule or mixture molecule is involved in the separation of an ion-pair, in other words , there it forms solvent separated ion-pair. The formation of solvent separated ion-pair IS In

accordance with the decrease in A 011/ (Table I).

Acknowledgement TN S thanks the UGC, New Delhi for awarding the

fellowship for carrying out research under FIP Programme.

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