electrosorption of cellosolve at ethyl mercury/kcl solution...

Indian Journal of CbemlstryVol. 16A, May 1978. pp. 391-394

Electrosorption of Cellosolve at Ethyl Mercury/KCl Solution InterfaceM. v., RAMANAMURTI, B. V. APPARAO & R. K. SINGH

Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005

Received 4 A pf'il 1977; accepted 26 N ouember 1977

Adsorption of ethyl ceUosolve at the mercury/O·l0 m KCI (aq.) solution interface has beenstudied through equiUbrium double layer capacity measurements. Langmuir's adsorptionisotherm is obeyed with rs=4·91 x 10-10 mol cmos and ~Gomax = -3·73 kcal mol'

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42 7i'0!

0-2>

RAMANAMURTI " Ill.: ELECTROSORPTION OF ETHYL CELLOSOLVE

(0)

4

o o 4) 0-0·6D 00 e -0.7o 0 c;: 0 Q:~:

~-,.o..0 0

~,','~-"2

-e

·0.4-2

'0.6 c c

~~----40------Q~--~~__--o~_6...uZ• ·'.0>

. '.2

Fig. 3 - (a) Electrode charge as function of surface excessof ethyl cellosolve at constant potential [Potential indi-cated on each line]. (b) Electrode potential as a functionof surface excess of ethyl cellosolve at constant charge

[Charge indicated on each line]

v

'" A-e-'"0to .. u,

E 0.06 w

N~0s- -0

0 "-is?.. O.O~V"IL!'

0·01

0·04 c·oe 0.11 0." 0.1~c ••~_lojll

'Eig. 4 - Test for Langmuir's adsorption isotherm for ethylcellosolve: (A) E = -1'0, (B) -0'9, (C) _0'8, (D) -0·7,

(E) -0'6, (F) -0'5 V vs NeE

o

0.0%

of E and increases with decrease in E. Themaximum r.,f values (rmu) obtained at Es, -O·70Vvs NCE (cf. Fig. 2) for various concentrations havebeen employed in plotting C.,fjrmu. vs l/CA (cf.broken line G in Fig. 4). The plot obtained is linear.The value of rs obtained thereby, viz. 4·91X to-10mol em? is independent of E. The maximumof surface coverage (6=rA/rS) attained in thepresent work is 0·70.

,

'7f~.- 3.

II!>C1I

- E Vs NeE (\loll.)

Fig. 5 - Standard free energy of adsorption as a functioDof electrode potential for ethyl cellosolve

0.1 0.3 0·4 0.50.3 e

-0.5-2·0

Fig. 6 - Ep.c as a function of (a) logarithm of bulk concen-tration of ethyl cellosolve and (b) as a function of surface

coverage of ethyl cellosolve

The standard free energy of adsorption (AGO)has been calculated from Eq. (4) given by Conwayand Barradass for Langmuir's adsorption isotherm:

In(SS'S._6_)=_ AGO ..• (4)c, 1-6 RTAt 6=0·3, the values of AGOhave been calculatedat various electrode potentials and the dependenceof 3Zo on E (d. Fig. 5) is found to be quadraticas expected for simple neutral organic substances.The value of K?;~ax (-3·73 kcal mol+) whencomparedt 0 that of ethylene glycol8 (-2·02 kcalmol-I) is a consequence of the relatively weakerintramolecular hydrogen bonding of ethyl cello-solve molecules than that of ethylene glycol withwater molecules.

Shift of Ep•c with log C.,f and with 6 - The poten-tial of zero charge of mercury in the pure base elec-troyte solution shifts towards less negative potentialswith increasing concentration of ethyl cellosolve(d. Fig. 6a). This indicates that ethyl cellosolveis adsorbed on mercury with the hydrocarbonchain facing the electrode and functional group inthe solution phase. The shift of Ep. with surfacecoverage of ethyl cellosolve (d. Fig. 6b) is linear

393

INDIAN J. CHEll., VOL·t6A; MAy·t978

suggesting thereby a single stable orientation of Referencesethyl cel1osolve throughout the coverage region'.

Acknowledgement

The authors are grateful to the UGC 'and CSIR,New Delhi, for the financial assistance to B. V.Apparao and R. K. Singh respectively.

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L GRAHAME, D. C., J. Am. chem. Soc., 63 (1941), 207.'2; GRAHAME, D. C., J. Am. chem, Soc .• 71 (1949), 2975.3; TRASATTI, S., J. eleciroanal. Chern.• 28 (1970), 257.4; DUTKIEWlPZ,;E •• GARRISH, J. D. & PARSoNS, R., J: eleo-

; troanal. Chem., 16 (1968), 505. .5~ CONw*"\[, ..13.. E. & BARRADAS, R. G., Electrochim. tfcta,:,5

(1961). 319. . .. .6; TRA~ATTr;. S.,:1- electroanal. Chem., .53. (1941), 335.