The Adsorption of N-Amyl-Alcohol at Electrified Mercury - Aqueous Sodium Halide Interfaces.

Transcription

1 Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1964 The Adsorption of N-Amyl-Alcohol at Electrified Mercury - Aqueous Sodium Halide Interfaces. Troy Haskell Tidwell Jr Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: Recommended Citation Tidwell, Troy Haskell Jr, "The Adsorption of N-Amyl-Alcohol at Electrified Mercury - Aqueous Sodium Halide Interfaces." (1964). LSU Historical Dissertations and Theses This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact gradetd@lsu.edu.

2 T h is d is s e r ta tio n h a s b een m ic r o film e d e x a c tly a s r e c e iv e d T ID W E L L, J r., T roy H a sk e ll, TH E A D SO RPTIO N O F N -A M Y L ALCOHOL AT E L E C T R IF IE D M ERCURY-A Q U EO U S SODIUM HALIDE IN T E R FA C E S. L o u isia n a State U n iv e r sity, P h.d., 1964 C h e m istr y, p h y sic a l U n iv e r s ity M ic r o film s, In c., Ann A rb o r, M ichigan

3 THE ADSOBPTION OP N-AMYL ALCOHOL AT ELECTRIFIED MERCURY - AQUEOUS SODIUM HALIDE INTERFACES A D i s s e r t a t i o n Subm itted to th e G raduate F a c u lty o f th e L o u ie la n a S t a t e U n iv e rs ity and A g r i c u l t u r a l and M echanical C o lle g e In p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts f o r th e d e g re e o f D o cto r o f P hilosoph y i n The D epartm ent o f C hem istry by Troy H a sk e ll T id w e l l,j r. B.S., N orth T exas S ta te U n iv e r s ity, 1959 M.S., N orth T exas S t a te U n iv e r s ity, I960 A u g u st, 1964

4 ACKNOWLEDGEMENT The a u th o r would l i k e to tak e t h i s o p p o rtu n ity to thank h is m ajor p r o f e s s o r, Dr. Paul D elahay, whose encouragem ent and a d r lc e made t h i s work p o s s ib le. 11

5 TABIE OF CONTENTS ACKNOWLEDGMENT... i i PAGE LIST OF TABLES... LIST OF FIGURES... LIST OF PLATES... ABSTRACT... iv v l l l lx CHAPTER I. INTRODUCTION... 1 I I. EXPERIMENTAL... 5 I I I. RESULTS... IV. CONCLUSION BIBLIOGRAPHY...?5 VITA

6 LIST OF TABLES TABLE PACE I. S u rfa c e T e n sio n of n-amyl A lc o h o l; 0.1 M NaF - Mercury I n t e r f a c e s I I. I I I. IV. S u rfa c e T e n sio n o f n-amyl A lc o h o l; 0.1 M NaCl - Mercury I n t e r f a c e s S u rfa c e T e n sio n o f n-amyl A lc o h o l; 0.1 M Nal - Mercury I n t e r f a c e s Charge D e n sity o f th e Mercury E le c tr o d e In NaF - n-amyl A lcohol S o lu tio n s V. Charge D e n sity o f th e Mercury E le c tr o d e In NaCl - n-amyl A lcohol S o lu tio n s VI. Charge D e n s ity o f th e Mercury E le c tr o d e In Nal - n-amyl A lcohol S o lu tio n s lv

7 L IST OF FIGURES FIGURE PAGE 1. E l e c t r o c a p l l l a r y Curves f o r n-amyl A lcohol a t D if f e r e n t K olar C o n c e n tra tio n s In 0.1 M N a F E l e c t r o c a p l l l a r y Curves f o r n-anyl A lcohol a t D if fe re n t Molar C o n c e n tra tio n s In 0.1 M NaCl E l e c t r o c a p l l l a r y Curves f o r n-anyl A lcohol a t D if fe re n t Molar C o n c e n tra tio n s In 0.1 M Nal... 1*4-4. The Charge D en sity on the Mercury E le c tro d e In 0.1 M NaF a s a F u n c tio n of n-amyl A lcohol C o n c e n tra tio n The Charge D en sity on the Mercury E le c tro d e In 0.1 M NaCl a s a F u n c tio n o f n-anyl A lcohol C o n c e n tra tio n The Charge D en sity on th e Mercury E le c tro d e In 0.1 M Nal a s a F u n c tio n of n-amyl A lcohol C o n c e n tra tio n S u rface T en sio n a s a L ogarithm ic F u n c tio n o f n-amyl A lcohol C o n c e n tra tio n In 0.1 M NaF a t C onstant T em perature S u rface T en sio n a s a L ogarithm ic F u n ctio n o f n-amyl A lcohol C o n c e n tra tio n In 0.1 M NaCl a t C onstant P o t e n t i a l S u rface T en sio n a s a L o g arith m ic F u n c tio n o f n-amyl A lcohol C o n c e n tra tio n In 0.1 M Nal a t C onstant P o t e n t i a l v

8 PAGE The S u rfa c e E xcess o f n-amyl A lcohol In 0.1 M NaF a s a F u n c tio n o f P o t e n t i a l... The S u rfa c e E xcess o f n-amyl A lcohol In 0.1 N NaCl a s a F u n c tio n o f P o t e n t i a l... The S u rfa c e E xcess o f n-amyl A lcohol i n 0.1 H Nal as a F u n c tio n o f P o t e n t i a l... The S u rfa c e E xcess o f n-amyl A lcohol In 0.1 N NaF a s a F u n c tio n o f Charge D en sity... The S u rfa c e E xcess o f n-amyl A lcohol In 0.1 H NaCl a s a F u n c tio n o f Charge D en sity... The S u rfa c e E xcess of n-amyl A lcohol In 0.1 H Nal a s a F u n c tio n o f Charge D en sity... The S u rfa c e P re s s u re o f n-amyl A lcohol I n 0.1 N NaF vs. Charge D en sity... The S u rfa c e P re s s u re of n-amyl A lcohol In 0.1 M NaCl v s. Charge D en sity... The S u rfa c e P re s s u re o f n-amyl A lcohol In 0.1 M Nal vs. Charge D en sity... The P o t e n t i a l Drop A cross th e In n e r L ayer v s. S u rfa c e E xcess a t C o n sta n t Charge In 0.1 N a F... The P o t e n t i a l Drop A cross th e In n e r Layer v s. S u rfa c e E xcess a t C o n sta n t Charge In 0.1 NaCl... The P o t e n t i a l Drop A cross th e In n e r L ayer v s. S u rfa c e E xcess a t C o n sta n t Charge in 0.1 Nal h ? vi

9 FIGURE PACE 82. The P o t e n t i a l Drop A cross th e In n e r L ayer v s. P o t e n ti a l a t C o n stan t C o n c e n tra tio n in 0.1 H N a F * The P o t e n t i a l Drop A cross th e In n e r L ayer v s. P o t e n t i a l a t C o n sta n t C o n c e n tra tio n In 0.1 MNaCl... 3^ 24. The P o t e n t i a l Drop A cross th e In n e r L ayer v s. P o t e n t i a l a t C o n stan t C o n c e n tra tio n In 0.1 M Nal The P o t e n t i a l Drop A cross th e O u ter L ayer v s. P o t e n t i a l a t C o n stan t C o n c e n tra tio n In 0.1 N a F The P o t e n t i a l Drop A cross th e O u ter L ayer v s. P o t e n t i a l a t C o n stan t C o n c e n tra tio n In 0.1 NaCl... 3? 27. The P o t e n t i a l Drop A cross th e O u te r L ayer v s. P o t e n t i a l a t C o n stan t C o n c e n tra tio n In 0.1 Nal The Change In th e R e c ip ro c a l C a p ac ity v s. C o n c e n tr a tio n a t C o n stan t Charge In 0.1 M NaF * The Change In th e R e c ip ro c a l C a p a c ity v s. C o n c e n tra tio n a t C o n stan t Charge In 0.1 M NaCl The Change in th e R e c ip ro c a l C a p a c ity vs. C o n c e n tra tio n a t C o n stan t Charge In 0.1 M Nal * Coverage v s. Change In R e c ip ro c a l C a p ac ity In 0.1 H NaF Coverage v s. Change In R e c ip ro c a l C a p acity in 0.1 MNaCl * Coverage v s. Change In R e c ip ro c a l C a p acity In 0.1 MNal v l l

10 L IST OP PLATES PLATE I. PACE The Lippmann C a p illa r y E le c tr o m e te r... 8 vlll

11 ABSTRACT The e l e c t r o c a p l l l a r y d a ta f o r n-am yl a lc o h o l over th e c o n c e n tr a tio n range M was ta k e n In 0.1 M NaF, 0.1 N NaCl, and 0.1 N Nal. The p o t e n t i a l range I n v e s t ig a te d, v a ry in g somewhat w ith th e system, was In c lu d e d In th e range to -1.2 v o l t s v e rs u s the norm al calom el e le c t r o d e. The te m p e ra tu re of the e x p e rim e n ta l s o l u t io n s wsb 25 C, which was determ ined by th e room te m p e ra tu re. An a tte m p t was made to e s t a b l i s h th e a d s o rp tio n Iso th e rm s f o r n-am yl a lc o h o l In th e se e l e c t r o l y t e s by the methods of s u r f a c e p re s s u re a n a l y s i s and r e c ip r o c a l c a p a c ity a n a l y s i s. T his n e c e s s ita te d th e c a l c u l a t i o n o f th e charge d e n s i t y, th e s u rfa c e e x c e s s, th e f r a c t i o n a l c o v e ra g e, th e s u r fa c e p r e s s u re and the r e c ip r o c a l c a p a c ity d a ta from th e e l e c t r o c a p l l l a r y d a ta. From th e s u r f a c e p re s s u re a n a l y s i s, th e re p u ls iv e f o r c e s betw een a d so rb ed m olecules a re shown to be q u ite sm all. The method is not s u f f i c i e n t to d eterm in e th e forms of th e is o th e rm s. The NaF system I s shown to f i t th e iso th e rm r e c e n tly d ev eloped by H elfan d, F r is c h, and Lebow itz a t low c o v erag e s and th e Frum kln Isotherm a t h ig h co v erag es. T h is Im p lies weak i n t e r a c t i o n betw een th e m ercury and th e adsorbed a lc o h o l. The NaCl and Nal c a se s could lx

12 n o t be a n aly ze d by th e r e c i p r o c a l c a p a c ity method due to th e I n t e r f e r e n c e of th e a n io n a d s o r p tio n. These system s c o rre sp o n d to mixed a d s o r p t io n and c a n n o t be a n aly ze d on th e b a s i s o f p r e s e n t th e o ry. x

13 CHAPTER I INTRODUCTION Through th e e f f o r t s o f a number o f w o rk e rs, the k i n e t i c s o f many ty p e s o f e le c t r o d e p ro c e s s e s have been w e ll c h a ra c t e r i z e d. Only In r e c e n t y e a r s, how ever, h as th e phenomenon o f s p e c i f i c a d s o r p tio n a t charged I n t e r f a c e s been c o n sid ere d from a m onem plrlcal b a s i s. D elahay and M o h lln er developed In t h i s la b o r a to r y an e q u a tio n d e s c r ib in g th e a d s o rp tio n o f n e u t r a l su b s ta n c e s based on th e lo g a r ith m ic Iso th erm o f T em kin.1,2 The problem o f s p e c i f i c a d s o rp tio n may be d iv id e d I n t o th e two c a t e g o r i e s o f e q u ilib riu m s t u d i e s and k i n e t i c s t u d i e s. Of th e s e tw o, the e q u ilib riu m d a ta must f i r s t be o b ta in e d, s in c e th e r a t e e q u a tio n s w i l l c o n ta in as p a ra m e te rs such q u a n t i t i e s a s e le c tr o d e c h a rg e, su rfa c e e x c e s s o f ad sorbed m a t e r i a l, and th e s ta n d a rd f r e e energy o f a d s o r p tio n. Once th e a d s o r p tio n iso th e rm has been e s t a b l i s h e d, th e s e q u a n t i t i e s become c a l c u l a b l e. As t h e r e Is a t p r e s e n t no method a v a i la b l e f o r p r e d i c ti n g P. D elahay and D.M. M ohllner, "R ate E q u atio n f o r A d s o rp tio n of a N e u tra l S u b stan ce a t a M etal E l e c t r o l y t e I n t e r f a c e ", J. P hvs. Chem (1962). 2 P. D elahay and D.M. M ohllner, "R ate E q u a tio n f o r A d s o rp tio n of a N e u tra l S u b stan ce a t a M etal E l e c t r o l y t e I n t e r f a c e ", J. Am. Chem. Soc.. 8*». 424? (1962). 1

14 th e form o f t h i s Is o th e rm, i t must be e s t a b l i s h e d by e x p e rim e n t. The e x p e rim e n ta l e s ta b lis h m e n t o f a d s o r p t io n Iso th e rm s h a 8 proved to be d i f f i c u l t. The p r o p e r t i e s w hich can be m easured a r e I n t e r f a c i a l t e n s io n, s u r f a c e c o n c e n tr a ti o n, o r e le c t r o d e c a p a c ity. Only w ith s u r f a c e c o n c e n tr a tio n d a ta can th e a d s o r p t io n Iso th erm ( s u r f a c e c o n c e n tr a tlo n - b u lk a c t i v i t y r e l a t i o n ) be d i r e c t l y e s t a b l i s h e d, and th e s e d a ta a r e n o t p r e s e n t l y a c c u r a te enough t o d i s t i n g u i s h c l e a r l y betw een th e p o s s ib le Iso th erm fo rm s. S u rfa ce c o n c e n tr a tio n may be o b ta in e d from b o th l n t e r f a c l a l t e n s io n and c a p a c ita n c e d a t a, b u t th e su b se q u e n t I n t r o d u c t io n o f e r r o r a g a in p r e c lu d e s th e c h o ic e o f an iso th e rm. I f e x p e rim e n ta l and t h e o r e t i c a l s u r f a c e p r e s s u r e - b u lk a c t i v i t y r e l a t i o n s a re com pared, more s a t i s f a c t o r y d i s t i n c t i o n s may be made. Both c a p a c ita n c e and l n t e r f a c l a l t e n s io n m easurem ents g iv e r i s e to s u r f a c e p r e s s u r e d a ta o f a b o u t 1% a c c u ra c y. Iso th e rm s can th e n be t e s te d by a p l o t o f s u rfa c e p r e s s u r e a g a i n s t th e lo g a rith m o f th e b u lk a c t i v i t y a t c o n s ta n t c h a rg e a s was done by P a rso n s. The sh ap e and p o s i t i o n o f th e cu rv e depend on th e v a lu e s of th e Iso th erm c o n s ta n ts and th e f r e e en erg y o f a d s o r p tio n a t th e chosen c h arg e o n ly. The s u rf a c e p r e s s u r e method -'R. P a rso n s, "The S t r u c tu r e o f th e M ercury- E l e c t r o l y t e In te r p h a s e In th e P resen ce o f T h io u re a ", P ro c. Rov. Soc.. A 2 6 l. 79 (1961).

15 3 w i l l p e rm it an Iso th e rm c h o ic e, how ever, I f th e s u rfa c e p r e s s u r e r e l a t i o n I s a s i n g l e - c o n s t a n t e q u a tio n o f s t a t e. I n t r o d u c t io n o f a second p a ra m e te r c a u s e s t h i s method to be I n s e n s i t i v e to Iso th e rm type. The lim ite d s u c c e s s of th e s u r fa c e p r e s s u r e method su g g e ste d t h a t th e c a p a c ity would p ro v id e th e most s e n s i t i v e it m ethod of Iso th erm d e te r m in a tio n. The r e c i p r o c a l c a p a c ity r e s u l t s from d i f f e r e n t i a t i o n o f th e c h arg e v e rs u s p o t e n t i a l c u r v e s, and a lth o u g h t h i s w i l l m agnify th e d i f f e r e n c e s In th e Is o th e rm s, th e d a ta a n a l y s i s becomes more d i f f i c u l t due to th e c o m p lica te d r e l a t i o n s h i p s betw een th e c a p a c ity, th e c h a rg e, and th e Iso th e rm p a ra m e te rs. T his I n v e s t i g a t i o n I s a t e s t of th e m ethods d is c u s s e d above f o r th e d e te r m in a tio n of th e a d s o r p tio n Iso th erm of n-am yl a lc o h o l In aqu eo u s sodium h a lid e s o lv e n ts a t e l e c t r i f i e d m ercury i n t e r f a c e s by th e s u r f a c e te n s io n m ethod. N-amyl a lc o h o l was chosen b e c a u se p re v io u s work In t h i s la b o r a to r y showed t h a t I t s a d s o r p t io n m ight be d e s c r ib e d by th e Temkln lo g a r ith m ic isotherm.-* The sodium s a l t s were ch o sen In o rd e r to e lim in a te c o m p e titiv e a d s o r p t io n from th e c a t io n In th e s u p p o rtin g e l e c t r o l y t e. k R. P a rso n s, U npublished com m unication. * B rel t e r and F. D elahay, "A d s o rp tio n o f N e u tra l S u b s ta n c e s from E l e c t r o c a p l l l a r y Curves and d o u b le Layer D i f f e r e n t i a l C a p a c i t i e s ", J. Am. Chem. S o c., 81, 2938 ( ).

16 The a n io n s e r i e s f l u o r i d e, c h lo r i d e, Io d id e was chosen so t h a t the changes In th e a lc o h o l a d s o r p t io n could be B tu d led a s a f u n c tio n o f th e a n io n c o m p e titio n. E le c t r o - c a p i l l a r y work has shown t h a t f lu o r id e Io n I s very weakly a d s o rb e d, c h lo r id e Ion a d so rb e d, and Io d id e Ion s tr o n g ly a d s o rb e d.^ In each o f th e th r e e s u p p o rtin g e l e c t r o l y t e s, the l n t e r f a c l a l te n s io n betw een a m ercury c a th o d e and the s o l u t i o n was m easured a s a fu n c tio n o f b o th p o t e n t i a l d i f f e r e n c e betw een th e m ercury and th e s o l u t i o n and a lc o h o l c o n c e n tr a tio n. For t h i s p u rp o se, a Lippmann e le c t r o m e t e r, w hich w i l l be d e s c rib e d l a t e r, was c o n s tr u c te d. ^D. C. Grahame, "The E l e c t r i c a l Double Layer and th e Theory of E l e c t r o c a p l l l a r l t y ', Chem. R e v s., hi. h h l (19h7).

17 CHAPTER I I EXPERIMENTAL A ll s o lu tio n s were p rep ared from A nalyzed Reagent g ra d e s a l t s w ith o u t f u r t h e r p u r i f i c a t i o n. The p u r if ie d g ra d e amyl a lc o h o l was d i s t i l l e d and th e m iddle f r a c t io n ta k e n. T his a lc o h o l was shown to be c h ro m a to g ra p h lc a lly homogeneous. The w a te r used was d i s t i l l e d w a te r which was r e d i s t i l l e d from b a s ic potassium perm anganate, and sto re d fo r no more than a few days In Pyrex c o n ta in e r s b e fo re u s e. The su p p o rtin g e l e c t r o l y t e s o lu tio n s were tr e a te d w ith a c t l v l t a t e d carbon b la c k a f t e r t h e i r p re p a ra tio n to a s s u r e removal o f t r a c e s o f s tro n g ly a d s o rb a n t o rg an ic m a te r ia ls. The carb o n was su b seq u en tly removed by d e c a n ta tlo n and c e n t r i f u g a t i o n b e fo re th e amyl a lc o h o l was added. The a lc o h o l s o lu tio n s were p rep a red by d is s o lv in g a weighed amount o f a lc o h o l In w a ter and th en d i l u t i n g w ith h a lid e s o lu tio n to produce a sto ck s o lu tio n of 0.1 M amyl a lc o h o l and 0.1 M sodium h a lid e. D ire c t d i s s o l u t i o n o f a lc o h o l I n to the h a lid e s o lu tio n s could n o t be accom plished a t t h i s c o n c e n tra tio n. By su c c e ssiv e d llu ts o n w ith 0.1 M sodium s o lu tio n of t h i s s to c k, th e more d i l u t e s o l u t io n s were p rep a red. A n itr o g e n purge was used to remove d is s o lv e d g a ses b e fo re th e su rfa c e 5

18 6 t e n s io n d e te r m in a tio n s w ere made. The n i tr o g e n was p r e t r e a t e d f i r s t w ith a c t i v a t e d c h a rc o a l In a d ry Ic e t r a p, th e n s a tu r a te d w ith w a te r. The w a t e r - s a tu r a t e d n i tr o g e n was d eoxygenated by p a s s in g th ro u g h a vanadyl s u l f a t e s o l u t io n above a z in c amalgam. The n itr o g e n was th e n passed th ro u g h a p r e s a t u r a t o r c o n ta in in g a sam ple o f th e s o l u t i o n w hich was In th e e le c t r o m e t e r c e l l. These p r e tr e a tm e n ts In su re d t h a t no f o r e ig n m a tte r would be In tro d u c e d I n to th e s o lu tio n to be s tu d ie d, t h a t th e oxygen c o n te n t o f th e s o l u t io n would be q u ite low, and t h a t th e c o n c e n tr a tio n o f th e s o l u t i o n d id n o t change a s a consequence o f th e n itr o g e n p u rg e. A fte r th e n itr o g e n was p assed th ro u g h th e s o l u t io n f o r about f i f t e e n m in u te s, i t was d ir e c te d o v er the s o l u t io n su rfa c e a s a p r o t e c ti v e b la n k e t to slow the s o l u t i o n o f a tm o sp h e ric g a s e s. The m ercury used was d i s t i l l e d in th e la b o r a to r y f o llo w in g an a i r o x id a tio n and s e v e r a l d i l u t e n i t r i c a c id tre a tm e n ts th ro u g h a w ashing tow er. The m ercury was th e n u t i l i z e d b e fo re th e fo rm a tio n of a s u rfa c e film. An H -c e ll p a r t i t i o n e d by a f i t t e d d is k o f fin e p o r o s i t y was u t i l i z e d. One com partm ent c o n ta in e d the a lc o h o l s o lu tio n s and th e c a p i l l a r y. The o t h e r c o n ta in e d o n ly th e su p p o rtin g e l e c t r o l y t e and th e r e f e r e n c e e le c t r o d e, a norm al calom el e l e c t r o d e. A ll p o t e n t i a l s a re g iv e n

19 7 In r e f e r e n c e to t h i s e l e c t r o d e. At t h i s p o in t th e l n t e r f a c l a l t e n s io n o f th e s o l u t io n mss d e te rm in e d. No a tte m p t was made to th e rm o s ta t th e s o l u t io n s. The room te m p e ra tu re v a rie d d u rin g th e e x p e rim e n ts betw een 25 C and 26 C. T h is e r r o r I s q u ite n e g l i g i b l e compared w ith c a l c u l a t l o n a l e r r o r s In v o lv ed. The a p p a ra tu s used was f i r s t d e s c r ib e d by Llppmann o v e r 80 y e a rs ago and has been s in c e m o d ifie d by many i n v e s t i g a t o r s. A d e t a i l e d d e s c r i p t i o n o f a modern c a p i l l a r y e le c tr o m e te r I s g iv e n by Hansen e t. e l. * E s s e n t i a l l y, th e p r e s s u r e n e c e s s a ry to m a in ta in the m ercury s o l u t i o n I n t e r f a c e a t a c a l i b r a t e d p o s i t i o n I n s id e a c a p i l l a r y I s m easured a s a f u n c tio n o f p o t e n t i a l d i f f e r e n c e betw een th e m ercury and a re fe r e n c e e l e c t r o d e In the s o l u t i o n. A m ercury m anom eter m easures th e p r e s s u re a p p lie d to th e c a p i l l a r y. The p r e s s u re system c o n s is te d o f com pressed n itr o g e n w hich was passed o v e r c h a rc o a l In a d ry Ic e t r a p to a v o id c o n ta m in a tio n o f th e m ercury. I f th e c o n ta c t a n g le betw een g l a s s and m ercury be tak en a s z e r o, th e s u rf a c e te n s io n can th en be c a l c u l a t e d from th e sim p le e q u a tio n : 2 JT «( /^lg^ i + ^ l g h 2 " p2gh3 ) X r B.S. H ansen, D.J. K elsh, and D.H. G rantham, "The In f e re n c e o f A d s o rp tio n from Double L ayer C a p ac ita n ce M easurem ents, J. PhyB. Chem ( ).

20 8 H a te I The L lppaann C a p illa r y E le c tro m e te r.

21 ATM TO POT 2^ v MCE-- MANOMETER TO MICROSCOPE FILTER STICK PLATE I

22 9 w here % s u rf a c e t e n s io n (dynes cm- *) d e n s ity o f th e Hg (gm s/ca^) h1- Hg h e ig h t o f nanom eter (cm) h^ - Hg h e ig h t o f c a p i l l a r y (cm) * d e n s ity o f s o l u t i o n (gms/cm^) h^* h e ig h t o f s o l u t i o n In c a p i l l a r y (cm) r* r a d iu s o f th e c a p i l l a r y (cm) The r a d iu s of th e c a p i l l a r y was d e te rm in e d by a c c e p tin g th e s u rfa c e te n s io n v a lu e s o f 0.1 M KC1 g iv e n by 2 D evanathan and P e r le s. The e l e c t r o c a p l l l a r y curve was ru n f o r 0.1 M KC1 a f t e r the c a p i l l a r y had been allow ed to soak in 0.1 M KC1 f o r s e v e r a l d ay s. I t h as been noted by S.R. C raxford t h a t th e a p p a re n t r a d iu s in c r e a s e s to a n e q u ilib riu m v a lu e upon so ak in g f o r a few d a y s.^ Once th e c a p i l l a r y had been c a l i b r a t e d, i t was n ev er allo w ed to d ry. The p o t e n t i a l betw een the m ercury and th e norm al calo m e l e le c tr o d e was f ix e d w ith a model K-2 Leeds and N o rth ru p p o te n tio m e te r powered by a 6 v o l t wet c e l l b a t t e r y. F req u en t ch eck s were made to I n s u re t h a t the p o t e n t i a l d id n o t d r i f t more th a n a 0.1 o f a m i l l i v o l t d u rin g th e d e te r m in a tio n o f a s u r fa c e te n s io n. I f such 2 H.A.V. D evanathan and P. P e r le s," T h e A d so rp tio n o f P otassium H a lid e s a t th e H ercury/w ater I n t e r f a c e ", T r a n s. Faraday S oc.. SO (195*0. ^S.R. C ra x fo rd, D i s s e r t a t i o n, O xford, 1936.

23 10 a d r i f t was d e te c t e d, th e d a ta were r e j e c t e d and th e d e te r m in a tio n was r e p e a te d. The h e ig h ts o f m ercury and th e s o l u t i o n h e ig h t needed f o r the c a l c u l a t i o n o f were measured w ith a c a th e to m e te r equ ip p ed w ith a v e r n i e r s c a le which co u ld be read to a t e n t h o f a m illim e te r. The I n t e r f a c e p o s i t i o n was obse rv e d w ith a Bausch and Lomb s te re o m lc ro sc o p e o f 80X h a v in g a m icrom eter d is k mounted In an e y e p ie c e. N itro g en p r e s s u r e was fix e d by a d ju s tm e n t o f th e o u t l e t o r i f i c e w hich was a m icrom eter g a s m e te rin g v a lv e. The c o n tin u o u s n itr o g e n flow expended a la r g e amount of n itr o g e n, b u t allo w ed th e c a p i l l a r y to assum e an e q u ilib riu m p o s i t i o n q u ic k ly. To In s u re t h a t th e m ercury In th e manometer was a t e q u ilib riu m when th e re a d in g was made, th e m ercury column was d is tu r b e d by a sudden In c r e a s e In p r e s s u r e from the a tm o sp h e ric s id e and th e re a d in g made when th e m ercury had ceased to o s c i l l a t e. I f t h i s caused a change In th e I n t e r f a c e p o s i t i o n, th e p r e s s u r e was a d ju s te d, and th e p ro c e ss re p e a te d. A fte r a d e te r m in a tio n, a d ro p o f m ercury was e x p e lle d from th e c a p i l l a r y to c r e a t e a f r e s h I n t e r f a c e. I t was noted th a t th e p resen c e o f oxygen caused a d i s t o r t i o n o f th e e l e c t r o c a p l l l a r y c u rv e s In th e sodium f l u o r id e medium. For t h i s re a s o n, s p e c ia l c a re was tak en to in s u re th e ab sen ce of

24 11 a tm o sp h e ric oxygen from th e s e s o l u t io n s. Oxygen I n t e r fe re d only s l i g h t l y In th e c h lo r id e system and n o t d e t e c t a b l y In th e Io d id e s o lu tio n s. The i n t e r f e r e n c e to o k th e form of a red u ced p o t e n t i a l dependence o f l n t e r f a c l a l te n s io n.

25 12 F ig u re 1 E l e c t r o c a p l l l a r y C urves f o r N-Amyl A lcohol a t D if f e r e n t M olar C o n c e n tra tio n in 0.1 M NaF. P o t e n t i a l s a re R e ferred to th e Normal Calom el E le c tr o d e in th e E l e c t r o l y t e w ith o u t A lco h o l.

26 POTENTIAL (VOLTS vs NjCE.) FIGURE I

27 13 F ig u re 2 E l e c t r o c a p i l l a r y C urves f o r N-Amyl A lco h o l a t D if f e r e n t M olar C o n c e n tra tio n s In 0.1 M NaCl. P o t e n t i a l s a r e R e fe rre d to th e Normal Calom el E le c tro d e in th e E l e c t r o l y t e w ith o u t A lc o h o l.

28 420 - SURFACE TENSION (DYNES C M '1) M PO TEN TIA L (V O LTS vs. N.CE.) FIGURE

29 F ig u re 3 E l e c t r o c a p l l l a r y C urves f o r N-Amyl A lco h o l a t D if f e r e n t M olar C o n c e n tra tio n s In 0.1 M Nal. P o t e n t i a l s a re R e fe rre d to th e Normal Calomel E le c tro d e In th e E l e c t r o l y t e w ith o u t A lco h o l.

30 420 I SURFACE TENSION (DYNES CM O 0 A 001M 0 0 I5M A 0.02 M M V M M M OIM POTENTIAL ( VOLTS vs N.C.E.) FIGURE 3

31 15 F ig u re U The Charge D e n sity on th e Mercury E le c tr o d e In 0.1 M NaF a s a F u n c tio n of N-Amyl A lcohol C o n c e n tra tio n. P o t e n t i a l s a r e R e fe rre d to th e Normal Calom el E le c tro d e i n 0.1 M NaF.

32 y -10 co m z> -5 UJ o POTENTIAL (V O LT S vs N.C.E ) FIGURE 4

33 16 F ig u re 5 The Charge D e n sity on th e Mercury E le c tr o d e In 0.1 M NaCl a s a F u n c tio n o f N-Anyl A lcohol C o n c e n tra tio n. P o t e n t i a l s a re R e fe rre d to th e Normal Calom el E le c tro d e In 0.1 M NaCl.

34 -10 CHARGE DENSITY (^COULOMBS CM" M M M M M i I PO T EN T IA L (VOLTS vs N.C.E.) FIGURE 5

35 17 F ig u re 6 The Charge D e n sity on th e Mercury E le c tr o d e In 0.1 M Nal a s a F u n c tio n of N-Amyl A lcohol C o n c e n tra tio n. P o t e n t i a l s a re R e fe rre d to th e Normal Calom el E le c tro d e In 0.1 n Nal.

36 0.015 M M M C 0.1 M -0.5 l I L J POTENTIAL (VOLTS vs N. C E. ) FIGURE 6

37 18 F ig u re 7 S u rfa c e T ension a s a L o g arith m ic F u n c tio n o f N-Aoyl A lc o h o l C o n c e n tra tio n In 0.1 M NaF a t C o n sta n t P o t e n ti a l.

38 SURFACE TENSION (DYNES CM ) V A -Q 2 V CONCENTRATION OP n-amyl ALCOHOL (MOLES LITER ) FIGURE 7

39 19 F ig u re 8 S u rfa c e T ension a s a L o g arith m ic F u n c tio n o f N-Amyl A lc o h o l C o n c e n tra tio n In 0.1 M NaCl a t C o n sta n t P o t e n ti a l.

40 SURFACE TENSION (DYNES CM ) O 085 V 0.75 V 0.65 V A 0.55 V 0.45 V OjOQ(O.I CONCENTRATION OF n-amyl ALCOHOL (MOLES LITER ) FIGURE 8

41 20 F ig u re 9 S u rfa c e T ension a s a L o g arith m ic F u n c tio n o f N-Amyl A lco h o l C o n c e n tra tio n In 0.1 M Nal a t C o n sta n t P o t e n ti a l.

42 3 6 0 SURFACE TENSION (OYNE CM"') V O V V V - a 6 5 V A V 2 -I.O0V -Ij05 V A -. g V CONCENTRATION OF n-amyl ALCOHOL (M/L) FIGURE 9

43 21 F ig u re 10 The S u rfa c e E xcess of N-Amyl A lcohol a t th e Mercury E le c tr o d e In 0.1 M NaF a s a F u n ctio n o f P o t e n t i a l,

44 M =T 7 0 SURFACE EXCESS (MOLES CM"Z X S ^ O w Q 0 6 M M M M 0.0I5M O q O 1O -^ q O v - 0 0! M o A PO TEN TIA L (VOLTS vs N.C E.) FIGURE 10

45 22 F ig u re 11 The S u rfa c e E xcess o f N-Amyl A lcohol a t th e Mercury E le c tr o d e in 0.1 M NaCl a s a F u n c tio n of P o t e n t i a l.

46 SURFACE EX C ESS r» o t * o o O (M OLES CM2 X I o " ) cn a t n o o o o r

47 23» F ig u re 12 The S u rface E xcess o f N-Amyl A lcohol a t th e Mercury E le c tr o d e In 0.1 M Nal aa a F u n ctio n o f P o t e n ti a l.

48 8 0 SURFACE EXCESS (MOLES CM* X 1 0 ") M PO TEN TIA L (V O L T S vs N. C.E.) FIGURE 12

49 Figure 13 The S u rfa c e E xcess o f N-Amyl A lcohol a t th e Mercury NaF, N-Aayl A lcohol I n t e r f a c e a s a F u n c tio n o f th e Charge D e n sity on th e M ercury.

50 8 0 SURFACE EXCESS (MOLES CM X I O " ) QOI M M Q 0 6 M M CHARGE DENSITY (/^C O U L O M B S CM2 ) FIGURE 13

51 25 F ig u re 1^ The S u rfa c e E xcess o f N-Amyl A lcohol a t th e Mercury M N ac lt N-Amyl A lcohol I n t e r f a c e a s a F u n c tio n o f Charge D e n sity on th e M ercury.

52 8 0 - SURFACE EXCESS (MOLES CMZX 10") QOI Q CHARGE DENSITY(/UCOULOM BS CM~2 ) FIGURE 14

53 26 F ig u re 15 The S u rfa c e E xcess o f N-Amyl A lcohol a t th e Mercury - N al, N-Amyl A lcohol I n t e r f a c e a s a F u n c tio n o f Charge D e n sity on th e M ercury. 0.1 M

54 5 0 SURFACE EXCESS (MOLES CM X 10 ) O O.Ot M M M HO -1 5 CHARGE DENSITY (>lcoulom BS CM2) FIGURE 15

55 2? F ig u re 16 The S u rfa c e P re s s u re o f N-Aoyl A lcohol In 0.1 M a F u n c tio n o f Charge D e n e lty on th e M ercury E le c tr o d e.

56 SURFACE PRESSURE { DYNES CM ) 20- O -I yixcoul. CM2-2 A - 4 ~6 aoi QOS 0.1 CONCENTRATION OF n-amyl ALCOHOL (MOLES LITERS') FIGURE 16

57 28 F ig u re 1? The S u rfa c e P re s s u re o f N-Amyl A lcohol In 0.1 M NaCl a s a F u n c tio n o f th e Charge D e n sity on th e M ercury E le c tr o d e.

58 o 6 /<.COU Q 4 " m _ SURFACE PRESSURE (DYNES CM 15 _ A 0» - 2 M - 4 ii - 6 ii 10 _ 5 - _L ± _L _L _L Q 0 8 Ol CONCENTRATION OF n-a M Y L ALCO HO L (M O L E S L IT E R S '1) FIGURE 17

59 29 F ig u re 18 The S u rfa c e P re s s u re o f N-Amyl A lcohol In 0.1 M Nal a s a F u n c tio n of th e Charge D e n sity on th e Mercury E le c tr o d e.

60 O 3 > ic O U L.C M 20 A - 3 SURFACE PRESSURE (DYNES O l CONCENTRATION OF n-am YL ALCOHOL (M O L E S LITERS- ') FIGURE 18

61 30 F ig u re 19 The P o t e n t i a l Drop A cro ss th e In n e r L ayer a s a F u n c tio n o f S u rfa c e Exmess o f N-Amyl A lcohol i n 0.1 H NaF S o lu tio n a t C o n sta n t Charge D e n sity a s I n d ic a te d by th e Number a t Each L ine.

62 POTENTIAL DIFFERENCE ACROSS INNER LAYER (VOLTS) 2 3 CD c 3 ) m t o CO c 31 > o m m X o m 05 0) o ro 2 O r m a> CO o 2, w X o o OD ro o n> 2 T

63 31 F ig u re 20 The P o t e n t i a l Drop A cross th e In n e r L ayer a s a F u n c tio n o f S u rfa c e E xcess o f N-Amyl A lcohol In 0.1 M NaCl S o lu tio n a t C o n sta n t Charge D e n sity a s In d ic a te d by th e Number a t Each L ine.

64 POTENTIAL DIFFERENCE ACROSS INNER LAYER (VOLTS) T ] O c 3) m r o

65 32 F ig u re 21 The P o t e n t i a l D if f e r e n c e A cross th e I n n e r L ayer a s a F u n c tio n o f S u rfa c e E x cess o f N-Amyl A lco h o l In 0.1 M Nal a t C o n stan t Charge D e n sity a s I n d ic a te d by th e Number a t Each L ine.

66 2 ] o c 33 m no in c D * - m m x om w in O ro oj POTENTIAL DIFFERENCE ACROSS INNER LAYER (VOLTS ) *0- I o ro i p r m 0) o ro x

67 33 F ig u re 22 The P o t e n t i a l Drop A cro ss th e In n e r L ay er a s a F u n c tio n o f P o t e n t i a l A cross 0.1 M KaF S o lu tio n a t C o n sta n t C o n c e n tra tio n o f Amyl A lc o h o l.

68 3 ] CD C JO m ro ro POTENTIAL (VOLTS vs N.C.E.) Q8-1.0 POTENTIAL DIFFERENCE ACROSS INNER LAYER ( VOLTS ) O o i> o 0) N> fo t r J I I 1 I L

69 3 4 F ig u re 23 The P o t e n t i a l Drop A cross th e In n e r L ayer a s a F u a c tlo n o f th e P o t e n ti a l A cross 0.1 M NaCl S o lu tio n a t C onstant C o n c e n tra tio n o f N-Amyl A lcohol.

70 POTENTIAL DIFFERENCE ACROSS INNER LAYER (VOLTS) i i i O p p o o <y> ro o ro ^ - i r 2 3 o c X m ro o j "0 O H m z H J> < O < w Z b m L 0 j i i i I l

71 35 F ig u re Zh The P o t e n t i a l Drop A cro ss th e In n e r L ayer a s a F u n c tio n o f th e P o t e n t i a l A cross 0,1 M Nal S o lu tio n a t C o n stan t C o n c e n tra tio n o f N-Amyl A lcohol,

72 i o -e> POTENTIAL DIFFERENCE ACROSS INNER LAYER (VOLTS) i o OJ i o K) i o G) C JO m ro t* T> O H m z H>r < o 5 5 rn I o a > i o I o QD o

73 36 F ig u re 25 The P o t e n t i a l D if fe re n c e A cross th e O u ter L ayer a s a F u n c tio n o f E le c tr o d e P o t e n t i a l a t C o n sta n t C o n c e n tra tio n o f N-Aayl A lcohol In 0.1 M NaF.

74 POTENTIAL DIFFERENCE ACROSS OUTER M 0.Q3M Q08M i i i ELECTRODE POTENTIAL (VOLTS vs. N.C.E.) FIGURE 2 5

75 37 F ig u re 26 The P o t e n ti a l D iffe r e n c e A cross th e O u ter L ayer a s a F u n c tio n o f E le c tr o d e P o t e n t i a l a t C o n sta n t C o n c e n tra tio n o f N-Amyl A lcohol In 0.1 N NaCl.

76 POTENTIAL ACROSS THE OUTER LAYER (VOLTS) S P o A Q O 0> e p o CD z o o

77 38 F ig u re 27 The P o t e n t i a l D if f e re n c e A cross th e O u te r L ayer a s a F u n c tio n o f E le c tr o d e P o t e n t i a l a t C o n sta n t C o n c e n tra tio n o f N-Aayl A lcohol In 0,1 M N al.

78 POTENTIAL DIFFERENCE ACROSS OUTER LAYER (V0LR3) O O b b o> a> o o 1

79 39 F ig u re 2f> The Change in th e R e c ip ro c a l C a p acity o f th e Mercury M NaF I n t e r f a c e a s a F u n c tio n o f th e Bulk C o n c e n tr a tio n v o f N-Amyl A lcohol a t C o n sta n t Charge D e n sity on th e M ercury in Coulombs c m " a s In d ic a te d by Each L ine,

80 r~ i "i. T i o 4 - o o - O O - 2 O o Q 1 X CM i -i 1 " '2 * - 0A -irf-s - I 10-4 _ o/^coul.cm* A A A A - 8 n ii A A , i _i i i CONCENTRATION OF n-amyl ALCOHOL ( MOLES LITER) FIGURE 28

81 Figure 29 The Change In th e R e c ip ro c a l C ap acity o f th e Mercury M NaCl I n t e r f a c e a s a F u n c tio n o f th e Bulk C o n c e n tra tio n o f N-Amyl A lcohol a t C o n sta n t Charge D e n sity on the M ercury In yucoulombs cm a s In d ic a te d by Each Line.

82 6 /ZC O U L. CM CM U. IO CONCENTRATION OF n-amyl ALCOHOL (M O LES LITER) FIGURE 29

83 F igure 30 The Change In th e R e c ip ro c a l C ap acity o f th e Mercury M Nal I n t e r f a c e a s a F u n c tio n of th e Bulk C o n c e n tra tio n o f N-Amyl A lc o h o l?a t C o n sta n t Charge D e n sity on th e M ercury In Coulombs cm a s In d ic a te d by Each L in e.

84 i 9 O A OyUCOUL. CM >2 I A A A A 0 A A -I Q 0 8 CONCENTRATION OF n-amyl ALCOHOL (M OLES LITER FIGURE 30

85 Figure 31 C overage of th e M ercury E le c tro d e by N-Amyl A lcohol a s a F u n c tio n o f Change In R e c ip ro c a l C a p a c ity o f th e M ercury M NaF, N-Amyl A lcohol I n t e r f a c e.

86 0.01 M O 0.0 3, 0 0 6, M CM O X CM i t f IO COVERAGE FIGURE 31

87 F ig u re 32 C overage o f th e M ercury E le c tro d e by N-Amyl A lcohol as a F u n c tio n o f Change In R e c ip ro c a l C a p a c ity o f the Mercury M NaCl, N-Amyl A lco h o l I n t e r f a c e.

88 5 - o o Q 0 3 M M 2 : x CM u 2k 3J* - i c f i i o I j i i i i - j i j i i [O COVERAGE FIGURE 32

89 Figure 33 C overage o f th e M ercury E le c tro d e by N-Amyl A lcohol as a F u n c tio n o f Change In R e c ip ro c a l C a p a c ity o f th e M ercury M N al, N-Aayl A lc o h o l. I n t e r f a c e.

90 8 6 O 0 a M M q - ^ (/XF CM X 10 ) O/ 2 Q COVERAGE FIGURE 33

91 CHAPTER I I I RESULTS The e l e c t r o c a p l l l e r y c u rv e s which w ere o b ta in e d a re p r e s e n te d In f i g u r e s 1-3. For th e sake o f c l a r i t y, some c o n c e n tr a tio n s o f a lc o h o l which were I n v e s t ig a te d a re n o t shown. These d a ta a r e found In t a b l e s I - I I I which Im m ediately fo llo w. The c u rv e s become a lc o h o l- in d e p e n d e n t a t b o th h ig h ly a n o d ic and c a th o d lc p o t e n t i a l s, I n d i c a ti n g t h a t th e a lc o h o l I s t o t a l l y d eso rb ed a t th e s e p o t e n t i a l s and th e curve only r e f l e c t s th e p r o p e r t i e s o f the s u p p o r tin g e l e c t r o l y t e. The maxima o f th e c u rv e s s h i f t In th e a n o d ic d i r e c t i o n m o n o to n ie slly w ith I n c r e a s in g a lc o h o l c o n c e n tr a tio n. The maximal a ls o a re d e p re ss e d as th e a lc o h o l c o n c e n tr a tio n I n c r e a s e s. There e x i s t s a therm odynam ic r e l a t i o n s h i p betw een th e e le c tr o d e c h arg e d e n s i t y, the l n t e r f a c l a l te n s io n, and th e p o t e n t i a l o f th e e le c t r o d e. T h is r e l a t i o n s h i p, w hich Is c l a s s i c a l, I s c a l le d the Llppmann e q u a tio n and I s w r i t t e n : w here I s the l n t e r f a c l a l te n s io n, E th e p o t e n t i a l, and q th e s u rfa c e c h arg e d e n s i ty o f th e e l e c t r o d e. A ll I n d ic a te d d i f f e r e n t i a t i o n s were done g r a p h i c a l l y. The charge on th e e le c t r o d e a t l a r g e n e g a tiv e p o t e n t i a l s I s n e g a t iv e, becomes l e s s n e g a tiv e a s th e ^5

92 46 p o t e n t i a l becomes wore a n o d ic, p a s s e s th ro u g h z e ro a t th e e l e c t r o c p a l l l a r y maximum, and becomes p o s i t i v e a s th e p o t e n t i a l I s made s t i l l more a n o d ic. T h is v a r i a t i o n I s I l l u s t r a t e d f o r th e s e c a s e s In f i g u r e s 4-6. These c u rv e s a r e o f th e ty p e o b serv ed w ith a d s o r p t io n o f n m u tra l s p e c i e s. 1 A gain, a l l th e d a ta which were ta k e n have n o t b e en graphed b u t have b een ta b u la te d In t a b l e s IV - VI. The s u rfa c e e x c e s s, V, o f th e a a y l a lc o h o l I s a therm odynam ic q u a n tity w hich can be d e te rm in e d from the e l e c t r o c a p i l l a r y c u rv e s. The r e l a t i o n s h i p I s w here X I s th e s u r f a c e te n s io n and jj< i s th e chem ical p o t e n t i a l of th e amyl a lc o h o l. S in ce yu. * J U 0 -, b e in g th e s ta n d a r d chem ical p o t e n t i a l, P may be o b ta in e d a s th e s lo p e o f th e p l o t o f V a g a i n s t ln a ( f i g u r e s 7-9 ). T h is c a l c u l a t i o n i s c l a s s i c a l. In th e ab sen ce o f o t h e r d a t a, f o r t h i s work th e a c t i v i t y o f th e amyl a lc o h o l has b een equ ated to th e c o n c e n tr a tio n. The P v e rs u s E p l o t s ( f ig u r e s 10-12) show t h a t Blomgren and J. 0*M. B o c h rls, "The A d so rp tio n o f B u ty l, Phenyl and N apthyl Compounds a t th e I n t e r f a c e M ercury-a queous Acid S o lu tio n ", J. P hvs. C h e n., 65, 2000 ( ). 2 N.K. Adams, The P h y sic s and C hem istry of S u r f a c e s. 3rd E d i t i o n, Oxford U n iv e r s ity tr e s s," ""Hew Y orfc.u.y T ; , p. 347.

93 t h e r e 1b a d s o r p tio n o v e r a range o f p o t e n t i a l s, and t h a t p becones p r a c t i c a l l y Indep en d en t of p o t e n t i a l o v er t h i s la r g e ran g e. The a d s o r p tio n and d e s o r p t io n of th e a lc o h o l can be se e n to o c c u r over v ery sm a ll p o t e n t i a l ra n g e s, a lth o u g h a t la rg e c o n c e n tr a tio n s, t o t a l d e s o r p tio n was n o t ach iev e d w ith in th e p o t e n t i a l v a lu e s I n v e s tig a te d, T hese p l o t s resem ble v e ry s tr o n g ly th e c u rv e s o b ta in e d by D elahay and B r e lt e r f o r amyl a lc o h o l in sodium p e r c h lo r a te. The r v e rs u s c h arg e d e n s ity a t c o n s ta n t c o n c e n tr a tio n p l o t s ( f ig u r e s 13-15) resem ble f i g u r e s I t i s more n e a rly e v id e n t h e re t h a t th e s u r f a c e e x c e ss i s n o t c o n c e n tr a tio n d e p e n d e n t a t la rg e n e g a tiv e charg e d e n s i t i e s, b u t I s d e te rm in e d by th e c h arg e d e n s ity. The s u r fa c e p r e s s u r e a n a l y s i s o f th e d a ta Is shown In f i g u r e s The s u r fa c e p r e s s u r e, ^, can be c a l c u l a t e d from th e d e f i n i t i o n : $ - * k- r + <}( E b-e ) w here f, q, and E have t h e i r u s u a l s i g n i f i c a n c e and th e s u p e r s c r i p t b r e f e r s to th e s u p p o rtin g e l e c t r o l y t e In th e ab sen ce of a d s o rb a n t a t th e g iv e n v a lu e of q. I f th e a d s o r p tio n p ro c e ss may be d e s c rib e d by a s i n g l e p a ra m eter ^B relter and D elahay, o p c l t

94 e q u a tio n o f s t a t e such a s H e n ry 's law, th e Langm ulr, V olm er, o r a v l r i a l e q u a tio n, a d i r e c t com p ariso n o f t h e o r e t i c a l and e x p e rim e n ta l p l o t s o f v e rs u s Inc should a llo w one to chose th e Iso th e rm w hich g iv e s th e b e s t f i t. k F o llo w in g th e method o f P a rso n s, an a tte m p t was made to su perim pose th e $ v e rs u s lo g c p l o t s a t d i f f e r e n t v a lu e s o f q. F ig u re 16 shows t h a t t h i s p roduces a b a d ly s c a t t e r e d p l o t and i n d i c a t e s t h a t th e NaF system h as more th an one a d j u s t a b l e p a ra m e te r. W hile b o th th e NaCl and Nal system s g iv e more c o n s l s t a n t r e s u l t s. The e q u a tio n f o r th e b e s t f i t i s n o t a v l r l a l e q u a tio n and th e c o n c e n tr a tio n range i s to o sm a ll to a llo w a d e c is io n among th e o th e r c h o ic e s. In a l l th r e e c a s e s, how ever, H e n ry 's law i s obeyed a t sm a ll c o n c e n tr a tio n s of a lc o h o l. A lthough no iso th e rm c h o ic e can be made, t h i s method of a n a l y s i s y i e l d s more In fo rm a tio n a b o u t th e a d s o r p tio n e q u ilib r iu m th a n does th e P d a ta a lo n e. The r e c i p r o c a l c a p a c i t i e s of th e d o u b le la y e r s were o b ta in e d by d i f f e r e n t i a t i o n o f th e p o t e n t i a l v e rs u s charg e p l o t s. These d a ta a r e g iv e n in f i g u r e s I t I s e v id e n t t h a t a f t e r t h i s number of o p e r a tio n s on th e o r i g i n a l d a t a, l i t t l e s i g n i f i c a n c e rem ains. However, th e cu rv es **R. P a rso n s, o p. c l t., A261, 79

95 49 ( I f drawn) a re q u i t e u n sy m m etrlcal in a l l c a s e s which w ould in tim a te t h a t th e Iso th e rm o f H e lfa n d, F r is c h and L ebow itz i s p o s s ib ly a p p l i c a b l e. B o t h th e u n c e r t a i n t i e s In tro d u c e d by th e s e v e r a l o p e r a tio n s in v o lv e d upon th e e x p e rim e n ta l d a ta and th e sm all c o n c e n tr a ti o n range co v ered by th e e x p e rim e n t, p re c lu d e an Iso th e rm c h o ic e by th e s e p l o t s. Coverage d a ta was o b ta in e d, and f i g u r e s show th e r e s u l t s. The co v erag e ( P/Pm /1X ) was c a lc u la te d by e s tim a tin g a v a lu e f o r Pmax from th e P v e rs u s E p l o t s in f i g u r e s o f a b o u t 10% In T h is e s tim a tio n may In v o lv e an e r r o r max w hich i s on th e o r d e r o f th e u n c e r t a i n t y a lr e a d y In P. Again th e d a ta a r e s c a t t e r e d, b u t some c o n c lu s io n s may be drawn a b o u t th e NaF system. 7 As P a rso n s has shown, th e r e should be a maximum a t th e c o v e ra g e o f i f th e HFL Iso th erm i s v a l i d and a maximum a t th e c o v e ra g e v a lu e o f 0.5 i f th e Frumkln Iso th e rm i s a b e t t e r d e s c r i p t i o n of th e system. The d a ta in f ig u r e 31 i n d i c a t e s t h a t th e HFL Iso th e rm fits a t low a lc o h o l c o n c e n tr a tio n s and th e Frum kln Iso th e rm a t high a lc o h o l c o n c e n tr a tio n s. T h is would c -'R. P a rso n s, U npublished Com m unication. ^E. H e lfa n d, H. L. F r is c h, J.L. L eb o w itz, "Theory o f th e Two-and O ne D im ensional R igid S p h ere F lu id s ", J. Chea. Phys.. ^ 4, 1037 (1961). 7 R. P a rso n s, U npublished Com m unication.

96 50 im ply t h a t the a lc o h o l i s n o t t i g h t l y bound to the m ercury s u r fa c e and th e a d so rb ed film 1b m obile w h ile th e co verage i s low, b u t a s th e co v erag e I n c r e a s e s, r e p u l s i o n betw een th e a lc o h o l m o lecu les im m o b iliz es th e f ilm, c r e a t i n g a d s o r p tio n " s i t e s ". T h at the r e c i p r o c a l c a p a c ity method was f r u i t l e s s f o r the c h lo r id e and io d id e system s i s n o t u n e x p ec te d, a s th e method i s b ased on the a ssu m p tio n t h a t the a d s o r p tio n would o ccu r from a s o l u t io n c o n ta in in g no s p e c i f i c a l l y ad so rb ed io n s. Only in t h i s case does th e c o n t r i b u t i o n to the m easured c a p a c ity from th e d i f f u s e d o u b le l a y e r not v a ry. The f i g u r e s 19-27* w h ile n o t d i r e c t l y concerned w ith th e iso th e rm e s ta b lis h m e n t, were made to show some p r o p e r t i e s of th e d o u b le la y e r s of th e s e sy ste m s. The f i g u r e s show th e p o t e n t i a l d i f f e r e n c e a c ro s s th e in n e r la y e r a t c o n s ta n t charge to be a l i n e a r f u n c tio n of s u rfa c e e x c e s s o f ad so rb ed a lc o h o l. F ig u re s 22-2k show t h a t th e p o t e n t i a l a c r o s s th e in n e r la y e r to be d e te rm in e d by th e p o t e n t i a l a c ro s s th e c e l l o n ly and to be in d ep e n d en t o f a lc o h o l c o n c e n tr a tio n. F ig u re s show th e dependence o f th e p o t e n t i a l d i f f e r e n c e a c r o s s th e o u te r l a y e r on th e e le c t r o d e p o t e n t i a l a t c o n s ta n t c o n c e n tr a tio n o f a lc o h o l.

97 CHAPTER IV CONCLUSION From th e s u r f a c e p r e s s u r e a n a l y s i s, some In fo rm a tio n may be e x tr a c te d c o n c e rn in g th e I n t e r a c t i o n s betw een th e a lc o h o l m o lecu les on th e m ercury s u r f a c e. A second v i r l a l c o e f f i c i e n t was c a l c u l a t e d f o r each o f th e s u r f a c e p re s s u re c u rv e s, In s p i t e o f th e f a c t t h a t th e s u r f a c e p r e s s u r e c u rv e s were n o t s t r i c t l y v i r l a l e q u a tio n s. T hese c o e f f i c i e n t s (w hich r e p r e s e n t tw ice th e m o le c u la r a re a o f th e ad so rb ed m o le cu le ) were on th e o r d e r of th e m o le c u la r a re a o f a CH^ group and p o s i t i v e. The fo r c e s may th e n be seen to be r e p u ls iv e f o r c e s b u t q u i te sm all a t th e co v erag es i n v e s t i g a t e d. The r e c i p r o c a l c a p a c ity method o f d a ta a n a l y s i s seems to be s a t i s f a c t o r y f o r th e e s ta b lis h m e n t of a d s o r p t io n Iso th e rm s. T here i s n eeded, f o r s u c c e s s f u l a p p l i c a t i o n o f th e m ethod, d a ta o th e r th a n i n t e r f a c i a l te n s io n. The c a p a c ity should be d i r e c t l y m easured, not o n ly b ecau se few er o p e r a tio n s must be p erfo rm ed on th e d a t a, b u t because th e c a p a c ity d a ta com plem ents th e l n t e r f a c l a l te n s io n d a ta. T hat th e s e d a ta a r e com plem entary was p o in te d out by B r e l t e r and D elahay.* * B r e lte r and D elah ay, o. c l t.. 8 1,

98 52 L a rg e r c o n c e n tr a tio n ra n g e s would d e f l n l t l y f a c i l i t a t e th e Iso th e rm c h o ic e. In th e s e c a s e s, how ever, th e c o n c e n tr a tio n rang e was lim ite d by s a t u r a t i o n a t a p p ro x im a te ly 0.2 H a t th e u p p er end and I n d i s t in g u i s h a b l e from th e s u p p o rtin g e l e c t r o l y t e a t th e lo w er end. N-amyl a lc o h o l Is n o t s tr o n g ly a d so rb e d, so t h a t c o n c e n tr a tio n s g r e a t e r th a n ab o u t 6 X 10 ^H a re n e c e s s a ry to observe a d s o r p tio n by l n t e r f a c l a l te n s io n m easurem ents.

99 TABLE I Surface Tension of N-Aayl Alcohol; 0 1 I! NaF-Hercury In te rfa c e s (dynes cb *) Alcohol M olarity E v o lts vs. N.C.E Vn Kj)

100 TABLE I (cont.) A lcohol lo la rlty E TOltS 6. N.C.E, * l? e-