ft} THE SULFUR DIOXIDE, OXYGEN, SULFURIC ACID CELL A t h e s i s submitted i n p a r t i a l f u l f i l l m e n t o f the requirements for t h e Degree o f M a s t e r o f A p p l i e d S c i e n c e i n t h e Department o f C h e m i s t r y JAMES A . L E I T H , B . A . S c . The U n i v e r s i t y o f B r i t i s h C o l u m b i a June, 1946. ACKNOWLEDGEMENT I w i s h t o acknowledge t h e helpful s u g g e s t i o n s and a s s i s t a n c e o f D r . W . F . S e y e r , under whose d i r e c t i o n the p r e s e n t work was c a r r i e d o u t . I would a l s o l i k e to t h a n k D r . B . P . S u t h e r l a n d o f the C o n s o l i d a t e d M i n i n g and S m e l t i n g Company f o r s u p p l y i n g some much needed equipment w h i c h c o u l d n o t be o b t a i n e d from the r e g u l a r s o u r c e s . TABLE OF CONTENTS, Page INTRODUCTION 1 OUTLINE OF THE PROBLEM 2 HISTORICAL 3 GENERAL THEORY 6 Gas Electrodes ••• Hydrates i n Aqueous Solution 6 7 PROBABLE MECHANISM OF CELL. REACTION 8 Anode Reactions 8 Cathode Reactions 8 O v e r a l l C e l l Reaction 9 DESIGN OF THE CELL OPERATION OF THE CELL 12 ' 14 P l a t i n i z i n g the Electrodes Degassing the Electrodes 14 ••• Changing the C e l l RESULTS 14 14 15 V a r i a t i o n of C e l l P o t e n t i a l with Cone. . . . . 15 E f f e c t o f the Rate of Sulfur Dioxide into the C e l l on the E . M . F 24 CONCLUSION 25 REFERENCES 26 BIBLIOGRAPHY 27 L I S T OF ILLUSTRATIONS Page 1. The V a r i a t i o n o f C e l l V o l t a g e w i t h Time U s i n g Different Electrode M a t e r i a l 4 2. Theoretical E.M.F. of C e l l 11 3. S u l f u r D i o x i d e , Oxygen, S u l f u r i c A c i d C e l l . . . . 13 4. C e l l Voltage v s . Concentration of Electrolyte,. 17 5. Freezing P o i n t Chart o f S u l f u r i c A c i d Hydrates. 20 6. The V a r i a t i o n o f C e l l V o l t a g e w i t h Time 23 KEY TO SYMBOLS f - f r e e energy change, - Faraday 96,500 coulombs M - mol f r a c t i o n N - normality n valence - T = temperature, t - time, calories degrees Centigrade hours X = per cent acid x = n o r m a l i t y o f e l e c t r o l y t e a t time J = conversion factor: "t" 1 c a l . - 4 . 1 8 3 joules 1 j o u l e = 9.87 cc atm. THE SULFUR DIOXIDE« OXYGEN*. SULFURIC ACID CELL P r o d u c t i o n o f s u l f u r i c a c i d "by p r e s e n t s t a n d a r d methods l e a v e s l i t t l e t o be d e s i r e d , elemental are u s e d . sulfur, e s p e c i a l l y when s u l f i d e o r e s and some b y - p r o d u c t gases However, the u t i l i z a t i o n o f the f r e e energy o f s u l f u r d i o x i d e i n the form o f e l e c t r i c a l production o f sulfuric acid offers energy f o r interesting the possibilities. The c e l l r e a c t i o n o f such a p r o c e s s i s g i v e n b y : SO., +- $Q% + H 0 t The f r e e energy change reaction H SO^ 4 involved i n t h i s i s made up o f the f r e e energy o f f o r m a t i o n o f s u l f u r i c a c i d p l u s the f r e e energy o f d i l u t i o n o f acid. •49,100 sulfuric The A F change i n f o r m i n g pure s u l f u r i c a c i d ' i s c a l o r i e s p e r m o l e , and f o r a more d i l u t e 1 acid it 2 would be even g r e a t e r . Any r e a c t i o n w h i c h i s accompanied by a l a r g e n e g a t i v e f r e e energy change i s spontaneous, hence from t h e above f r e e energy change we r e a l i z e i t would "be q u i t e p o s s i b l e t o produce s u l f u r i c a c i d i n an e l e c t r o l y t i c c e l l and a t the same t i m e draw o f f e l e c t r i c a l e n e r g y . By t h e use o f s u l f u r d i o x i d e i n the method i n d i c a t e d , a number o f o b j e c t i v e s c o u l d be a c h i e v e d . These i n c l u d e p r o d u c t i o n o f cheap d i l u t e a c i d f o r i n d u s t r i a l u s e s such as p i c k l i n g s t e e l o r l e a c h i n g copper o r o t h e r ores; p r o d u c t i o n o f c o n c e n t r a t e d a c i d where economic ( r o n d i t i o n s w a r r a n t , and abatement o f a t m o s p h e r i c p o l l u t i o n . OUTLINE OF THE PROBLEM I n the f o l l o w i n g e x p e r i m e n t s i t was p r o p o s e d t o determine the e l e c t r o m o t i v e f o r c e o f a c e l l s i m i l a r Pt, to SO,,: H^SO,,.: Oj, , P t at various concentrations o f s u l f u r i c a c i d . The above cell was s t u d i e d i n 1945 b y T . C . A s s a l y , and from h i s work i t was shown t h a t f o u r h y d r a t e s o f s u l f u r i c a c i d were s t a b l e i n solution. The w r i t e r proposed t o s t u d y the same c e l l w i t h d i f f e r e n t e l e c t r o d e m a t e r i a l t o t e s t the v a l i d i t y o f Assaly's results. The o v e r a l l e f f i c i e n c y o f the p l a t i n u m - e l e c t r o d e c e l l was b e l o w 50 p e r c e n t o v e r the g r e a t e r p a r t o f the acid r a n g e , so a p r e l i m i n a r y s t u d y was made t o f i n d an e l e c t r o d e c o m b i n a t i o n w h i c h would i n c r e a s e the c e l l e f f i c i e n c y . Lead e l e c t r o d e s were u s e d f i r s t b u t were soon d i s c a r d e d s i n c e an o x i d e f i l m formed i m m e d i a t e l y on b o t h t h e anode and cathode producing a v e r y low v o l t a g e . T e s t s were t h e n c a r r i e d o u t u s i n g t a n t a l u m m e t a l a t b o t h e l e c t r o d e s and a c o n s t a n t v o l t a g e was o b t a i n e d a f t e r about 24 h o u r s . The o f t h i s c e l l was b e l o w t h a t o f A s s a l y ' s b u t i t efficiency appeared t h a t a c o m b i n a t i o n o f p l a t i n u m and t a n t a l u m m i g h t g i v e the desired results. A c e l l made up o f a p l a t i n u m anode and a t a n t a l u m cathode was t h e n t e s t e d b u t t h i s s t i l l was n o t satisfactory. The e l e c t r o d e c o m b i n a t i o n was t h e n r e v e r s e d , and w i t h t a n t a l u m as anode and p l a t i n u m as cathode a g r e a t i n c r e a s e i n e f f i c i e n c y was o b t a i n e d . F i g . 1 shows t h e s e results graphically. As a r e s u l t o f t h e s e e x p e r i m e n t s i t was d e c i d e d t o d e t e r m i n e the a c t u a l e l e c t r o m o t i v e f o r c e o f the cell: T a , S 0 : H^SO^: 0,,, P t 4 at various concentrations of s u l f u r i c acid. \. HISTORICAL I n 1916 M e s s r s . M . De Kay Thompson and IT. J . Thompson* i n v e s t i g a t e d the c u r r e n t e f f i c i e n c i e s o f the o x i d a t i o n o f s u l f u r o u s a c i d and t h e y showed t h a t this o x i d a t i o n t a k e s p l a c e w i t h h i g h c u r r e n t e f f i c i e n c i e s even 5 i n strong s u l f u r i c acid solutions. Also for a given s u l f u r i c a c i d c o n c e n t r a t i o n the c u r r e n t e f f i c i e n c y d e c r e a s e s with increasing current density. M e s s r s . M . De Kay Thompson and A . P . Sullivan s t u d i e d the d e p o l a r i z a t i o n e f f e c t s o f s u l f u r d i o x i d e i n an e l e c t r o l y t i c c e l l u s i n g a p l a t i n u m anode. They found t h a t i t was p o s s i b l e to d e c r e a s e the p o l a r i z a t i o n a t the anode and t h u s d e c r e a s e the e q u i l i b r i u m v o l t a g e o f the c e l l b y the a d d i t i o n o f s u l f u r d i o x i d e . I t appeared from t h e i r e x p e r i m e n t s t h a t the p o l a r i z a t i o n was due t o the a c c u m u l a t i o n o f f r e e oxygen a t the anode. On a d d i t i o n o f s u l f u r d i o x i d e t o the a n o l y t e a r e a c t i o n o c c u r r e d between t h i s gas and the f r e e oxygen r e d u c i n g the p o l a r i z a t i o n e f f e c t s . M r . T . C . A s s a l y s t u d i e d the a c t u a l e l e c t r o m o t i v e f o r c e o f the cell: P t , S 0 : H^SO : 0 , P t l A X a t v a r i o u s c o n c e n t r a t i o n s o f s u l f u r i c a c i d and a t temperatures. different He found t h a t i n p l o t t i n g c e l l v o l t a g e versus c o n c e n t r a t i o n o f e l e c t r o l y t e t h a t a s t e p - w i s e c u r v e was formed; each o f the f o u r s t e p s c o r r e s p o n d i n g t o a h y d r a t e o f sulfuric acid. Other e x p e r i m e n t e r s have shown e v i d e n c e for t h e e x i s t e n c e o f t h r e e o f t h e s e h y d r a t e s b y f r e e z i n g methods. The e l e c t r o l y t i c method i n d i c a t e s t h a t the s u l f u r i c a c i d o h y d r a t e s are s t a b l e a t 25 C as w e l l as a t t h e i r freezing points. The e l e c t r o m o t i v e f o r c e o f the above c e l l was shown t o be dependent o n the t e m p e r a t u r e o f the electrolyte. - 6 The v o l t a g e i n c r e a s e d s l i g h t l y w i t h a d e c r e a s e i n t e m p e r a t u r e and approached a c o n s t a n t v a l u e a t l o w t e m p e r a t u r e s , GENERAL THEORY GAS ELECTRODES Gas e l e c t r o d e s commonly c o n s i s t o f a s o l i d c l a s s c o n d u c t o r , i n w h i c h a gas has been a b s o r b e d . firstRecent i n v e s t i g a t o r s have shown t h a t the emf d e v e l o p e d b y s o - c a l l e d gas e l e c t r o d e s i s a f u n c t i o n o f the f i r s t - c l a s s conductor i n w h i c h the gas i s c o n t a i n e d as w e l l as o f the gas itself. I n o t h e r w o r d s , gas e l e c t r o d e s are r e a l l y g a s - m e t a l electrodes s i n c e m e t a l s are commonly used t o absorb t h e s e g a s e s . The p o t e n t i a l s d e v e l o p e d by such g a s - m e t a l e l e c t r o d e s are for the p a r t i c u l a r m e t a l and g a s , and are r e l a t e d t o a b s o r b i n g power o f the m e t a l f o r the g a s . the The p o t e n t i a l s are known to v a r y g r e a t l y w i t h t h e n a t u r e o f the i n w h i c h the e l e c t r o d e s are immersed. specific electrolyte I t has a l s o been found t h a t t h e r e i s a somewhat d i f f e r e n t p o t e n t i a l d e v e l o p e d when the e l e c t r o d e i s s t a t i o n a r y t h a n when i t i s i n m o t i o n . latter e f f e c t may be shown b y moving the e l e c t r o d e o r b y k e e p i n g i t s t a t i o n a r y and moving the e l e c t r o l y t e . e l e c t r o l y t e may be moved by s t i r r i n g , c a u s i n g t h e t o f l o w p a s t t h e e l e c t r o d e , o r b y b u b b l i n g t h e gas the This The electrolyte through electrolyte. I t has been o b s e r v e d t h a t the amount o f gas needed to b r i n g about i t s e f f e c t on the p o t e n t i a l o f a m e t a l , i s v e r y small indeed. 1 I n f a c t , the p r e s s u r e o r s o l u b i l i t y o f the gas has l i t t l e o r no e f f e c t on the p o t e n t i a l . When a gas is b e i n g pumped o u t o f t h e s o l u t i o n l i t t l e e f f e c t i s o b s e r v e d on t h e p o t e n t i a l u n t i l the b u b b l i n g o u t o f the gas causes a stirring effect. HYDRATES I N AQUEOUS SOLUTION The number o f m o l e c u l e s o f w a t e r i n c o m b i n a t i o n w i t h one m o l e c u l e o f t h e d i s s o l v e d s u b s t a n c e , frequently i n c r e a s e s from the most c o n c e n t r a t e d t o t h e most d i l u t e s o l u t i o n s , as w i t h magnesium c h l o r i d e , manganese c h l o r i d e and copper c h l o r i d e . W i t h some s u b s t a n c e s the number o f m o l e c u l e s o f water h e l d i n c o m b i n a t i o n b y one m o l e c u l e o f the d i s s o l v e d substance may p a s s t h r o u g h a w e l l - d e f i n e d maximum as d i l u t i o n i s increased. the I n o t h e r c a s e s , the number o f m o l e c u l e s o f w a t e r h e l d i n c o m b i n a t i o n b y one m o l e c u l e o f the d i s s o l v e d substance may r e a c h a maximum v a l u e as the dilution i s i n c r e a s e d ; t h i s maximum v a l u e may t h e n r e m a i n p r a c t i c a l l y c o n s t a n t w i t h f u r t h e r i n c r e a s e s i n the dilution. The q u e s t i o n a r i s e s whether t h e s e h y d r a t e s are c h e m i c a l compounds o r whether t h e y r e p r e s e n t form o f c o m b i n a t i o n . some l e s s true stable That t h e y are u n s t a b l e i s shown b y the ease w i t h w h i c h t h e y are b r o k e n down b y h e a t . Most o f the w a t e r can be d r i v e n o f f from the above s o l u t i o n s a t a o temperature o n l y a l i t t l e above 100 C . The more complex h y d r a t e s a r e , t h e n , decomposed i n s o l u t i o n a t a c o m p a r a t i v e l y low temperature vapour. and the water i s g i v e n o f f i n t h e form o f I n t h e l i g h t o f t h e s e f a c t s the h y d r a t e s can s c a r c e l y be r e g a r d e d as t r u e c h e m i c a l compounds. I f however, we i n s i s t on c a l l i n g them c h e m i c a l compounds, we must admit t h a t they represent a v e r y low order o f s t a b i l i t y . I t i s the g e n e r a l o p i n i o n t h a t b o t h m o l e c u l e s and i o n s combine w i t h w a t e r , forming hydrates. I t seems t h a t m o l e c u l e s are c e r t a i n l y capable o f f o r m i n g h y d r a t e s , i n very concentrated the because s o l u t i o n s where the i o n i z a t i o n i s v e r y s m a l l , we o f t e n have c o n s i d e r a b l e h y d r a t i o n . That i o n s are capable o f c o m b i n i n g w i t h w a t e r i n s o l u t i o n i s shown by the magnitude o f the h y d r a t i o n i n many o f the d i l u t e solutions, where c h i e f l y i o n s and o n l y a few m o l e c u l e s are p r e s e n t . PROBABLE MECHANISM OF CELL REACTIONS ANODE REACTIONS The s u l f u r d i o x i d e f i r s t d i s s o l v e s i n the sulfuric a c i d e l e c t r o l y t e and t h e n adsorbs on t h e s u r f a c e o f the electrode: SO (gas) = SO^(solution) t (1) The s u l f u r d i o x i d e t h e n combines w i t h w a t e r as i n e q u a t i o n (2) ' S O + H 0 = S0~ + 2 H % ^ ^ z CATHODE JL (2) REACTIONS S i m i l a r l y , oxygen i s d i s s o l v e d i n the electrolyte and t h e n adsorbed on the s u r f a c e o f t h e e l e c t r o d e . • 0 (gas) 4 '=:" O^Csolution) (3) The oxygen t h e n combines w i t h water as i n e q u a t i o n £O F C * H.0 +• 2 ( - ) - 20H (4) OVERALL CELL REACTION The o v e r a l l c e l l reaction i s given by: S0 +£ O i mH^O - 2 The Hj,S0 4 (5) (N = X) c e l l r e a c t i o n can be d i v i d e d i n t o two p a r t s as s u c h : SO 2. +• J 0 a z +• io^ (6) mH O - H^SO^. (N - X ) (7) t 2 H % SO^ SO +- H O = H^SO^. a + mH O = H SO^ ( N =• X) t A d d i t i o n o f equations overall c e l l reaction. r e a c t i o n s o f equations (8) z (6) and (7) g i v e s t h e Hence a d d i t i o n o f t h e f r e e energy o f (6) and (7) w i l l g i v e the o v e r a l l f r e e energy change w i t h i n the c e l l . The v a l u e o f A F f o r (6) i s o b t a i n e d from t h e d i f f e r e n c e o f t h e f r e e equation energy o f f o r m a t i o n o f s u l f u r i c a c i d and t h e sum o f t h e f r e e energies o f f o r m a t i o n o f s u l f u r . d i o x i d e , w a t e r and o x y g e n . is* H s o + - A ~ 176,000 c a l o r i e s z ^is" \s.o£, ^ **° u » o F Oj. - - 71,740 c a l o r i e s - - 56,690 c a l o r i e s - zero T h e r e f o r e A F change = - 4 9 , 1 0 0 c a l o r i e s . The the free number o f a c c u r a t e measurements from w h i c h energy o f d i l u t i o n o f s u l f u r i c a c i d may be calculated i s limited. T a b l e s are a v a i l a b l e on the free energy o f d i l u t i o n o f t h e a c i d o n l y f o r d i l u t e s o l u t i o n s . 8 B r o n s t e d s t u d i e d the f r e e energy o f d i l u t i o n o v e r a r a t h e r wide range o f c o n c e n t r a t i o n s o f s u l f u r i c a c i d b u t a t • 9 t e m p e r a t u r e s r a n g i n g o n l y up t o 9 C . Harned and S t u r g i s I O and L e w i s and R a n d a l l a l s o s t u d i e d the f r e e energy o f t h i s a c i d , b u t o n l y o v e r a s m a l l range o f concentration. A s a t i s f a c t o r y t a b l e o f the f r e e energy o f d i l u t i o n a t 25°C f o r c o n c e n t r a t i o n s up t o 0 . 2 m o l f r a c t i o n s u l f u r i c a c i d has been worked o u t b y R a n d a l l and Cushman.* r e s u l t s w h i c h are the f r e e e n e r g i e s * F , o f the 2H + + S 0 ^ + mH 0 = R \ S 0 z reaction: (N-X) 4 Their (7) are g i v e n i n the t h i r d column o f T a b l e I , and the correspond- i n g v a l u e s o f mol f r a c t i o n M and p e r c e n t a c i d X i n t h e f i r s t and second columns r e s p e c t i v e l y . M TABLE I A F . Ccal.") X(%) AF, (k c a l . ) E(volts) 1.00 100.00 0 -49.1 1.065 .20 57.70 5270 -43.8 .950 .13 44.90 2915 -46.2 1.000 .10 37.70 1645 -47.5 1.030 .08 31.60 702 -48.4 1.048 .065 27.55 -85 -49.2 1.067 .05 22.28 -865 -50.0 1.084 .03 14.42 -2048 .02 10.00 .01 .002 .0009 -51.1 1.108 -2735 -51.8 1.122 5.21 -3702 -52.8 1.143 1.08 -5613 -54.7 1.185 -6547 -55.6 1.204 .487 A F A £x F x - r e p r e s e n t s the o v e r a l l c e l l reaction r e p r e s e n t s the f r e e energy o f d i l u t i o n By s u b s t i t u t i o n i n t h e f o r m u l a , E - -&F)(J) n f a calories J = 4.183 j o u l e s / c a l o r i e © assuming a temperature o f 25 C , t h e t h e o r e t i c a l v a l u e s o f t h e emf t h a t would be o b t a i n e d i n a c o m p l e t e l y r e v e r s i b l e c e l l are o b t a i n e d . Table I . The v a l u e s are g i v e n i n column 5 o f I n F i g , 2 t h e v a l u e s o f t h e emf g i v e n i n T a b l e I are p l o t t e d as o r d i n a t e s a g a i n s t c o n c e n t r a t i o n o f s u l f u r i c a c i d as a b s c i s s a . A h y p o t h e t i c a l c u r v e was drawn from 0 . 2 M t o 1 M s u l f u r i c a c i d , the range o f c o n c e n t r a t i o n where i n f o r m a t i o n on the f r e e energy o f d i l u t i o n was u n o b t a i n a b l e . DESIGN OF THE. CELL- A diagrammatic sketch o f the c e l l i s g i v e n i n F i g . 3. I t c o n s i s t e d o f two s t o p p e r e d f r i t t e d g l a s s v e s s e l s , anode and cathode compartments, each c o n t a i n i n g s u l f u r i c a c i d o f the same c o n c e n t r a t i o n . Each o f t h e s e v e s s e l s had a g l a s s tube e x t e n d i n g from i t , about two i n c h e s above fritted disc. the These v e s s e l s were connected b y means o f a r u b b e r tube c o n t a i n i n g a c l a y d i a p h r a g m . E l e c t r i c a l c o n t a c t was made b y two m e r c u r y f i l l e d glass leads. One end o f each l e a d was s e a l e d t o t h e stem o f i t s p a r t i c u l a r e l e c t r o d e ; the anode b e i n g a s t r i p o f t a n t a l u m and t h e cathode a p l a t i n i z e d p l a t i n u m g a u z e . The p o t e n t i a l was measured b y a p o t e n t i o m e t e r . The whole c e l l was s e t i n a c o n s t a n t temperature o b a t h w h i c h m a i n t a i n e d the temperature desired value. w i t h i n 0 . 0 5 C o f the 13 14 OPERATION OF THE CELL PLATINIZING THE ELECTRODES The p l a t i n u m e l e c t r o d e s were c o a t e d w i t h a l a y e r o f p l a t i n u m "black d e p o s i t e d e l e c t r o l y t i c a l l y from a t h r e e per cent s o l u t i o n o f c h l o r o p l a t i n i c a c i d . The e l e c t r o d e s were f i r s t c l e a n e d i n warm chromic a c i d and t h e n l o w e r e d i n t o the s o l u t i o n . A 1 2 - v o l t c i r c u i t was u s e d and a commutator a l l o w e d the c u r r e n t t o be r e v e r s e d a t d e s i r e d intervals. By means o f a s l i d i n g r e s i s t a n c e , the c u r r e n t was r e g u l a t e d so as t o produce a moderate e v o l u t i o n o f g a s . The d i r e c t i o n o f the c u r r e n t was r e v e r s e d e v e r y minute u n t i l a b l a c k and v e l v e t y c o a t i n g appeared on the s u r f a c e o f the electrodes. DEGASSING THE ELECTRODES A f t e r each r u n t h e e l e c t r o d e s were removed from the c e l l , washed i n d i s t i l l e d w a t e r , and degassed b y e l e c t r o l i z i n g them i n 6 N s u l f u r i c a c i d f o r a p p r o x i m a t e l y one h o u r . The d i r e c t i o n o f the c u r r e n t was r e v e r s e d e v e r y t e n m i n u t e s for the f i r s t f i f t y m i n u t e s , t h e n e v e r y minute f o r the ten minutes. last The p l a t i n u m e l e c t r o d e s were t h e n b o i l e d i n d i l u t e n i t r i c a c i d f o r t e n m i n u t e s forremove any p o i s o n i n g agents. F i n a l l y a l l t h e e l e c t r o d e s were washed i n b o i l i n g d i s t i l l e d water f o r f i f t e e n minutes. CHANGING THE CELL The oxygen and s u l f u r d i o x i d e i n l e t and o u t l e t c o n n e c t i o n s t o t h e c e l l were opened and the two h a l f - c e l l s were removed from the c o n s t a n t t e m p e r a t u r e b a t h . 15 After f l u s h i n g w i t h warm d i s t i l l e d w a t e r , t h e h a l f - c e l l s were d r i e d i n a warm oven t h e n washed w i t h s u l f u r i c a c i d e l e c t r o l y t e . The c e l l was t h e n s e t up a g a i n and c o n n e c t i o n s made t o s u l f u r d i o x i d e and oxygen t a n k s . the Seventy-five cubic c e n t i m e t e r s o f t e s t s u l f u r i c a c i d was t h e n added t o each h a l f c e l l and the e l e c t r o d e s p l a c e d i n t h e i r r e s p e c t i v e half-cells. The s u l f u r d i o x i d e and oxygen were o b t a i n e d from pressure tanks. for The d e s i r e d c o n c e n t r a t i o n o f s u l f u r i c a c i d each r u n was o b t a i n e d b y d i l u t i n g C P . a c i d w i t h water. distilled The e x a c t s t r e n g t h o f the a c i d was d e t e r m i n e d b y t i t r a t i n g a g a i n s t a s t a n d a r d NaOH s o l u t i o n u s i n g p h e n o l p h t h a l e i n as i n d i c a t o r . RESULTS VARIATION ffl? mgrT.- POTENTIAL WITH CONCENTRATION f Measurements were made o f c e l l p o t e n t i a l a t v a r i o u s o a c i d c o n c e n t r a t i o n s , ,-ajad a t 25 C , and t h e s e are shown i n Table I I . The f i r s t and second columns g i v e t h e n o r m a l i t y N and t h e p e r c e n t a c i d X and t h e t h i r d column the measured emf o f the c e l l . The v a l u e s o f t h e emf g i v e n i n T a b l e I I are t h e v a l u e s o b t a i n e d a f t e r t h e s u l f u r d i o x i d e and oxygen had b u b b l e d t h r o u g h t h e c e l l f o r n e a r l y 24 h o u r s and the p o t e n t i a l approached a c o n s t a n t v a l u e . cell 16 TABLE III X 1 E I (voits) 0.98 4.69 0.8270 3.04 13.94 0.8120 4.80 21.23 0.8000- 6.22 26.75 0.7990- 8.10 33.60 0.7960-- 10.24 40.82 0.7927 12.20 46.90 0.7896— 14.05 52.35 0.7889: 17.30 61.11 0.7882- 18.20 63.37 0.7690 21.35 70.79 0.7674- 24.31 77.17 0.7620^ 25.50 79.50 0.7121^ 26.61 81.70 0.678Q, 29.00 86.18 0.6752- 32.00 90.80 0.5800„ 33.20 93.90 0.4770 . 35.60 97.10 0.4657 The v a l u e s o f the emf g i v e n i n T a b l e I I are i n F i g . 4 as o r d i n a t e u s i n g the n o r m a l i t y o f t h e a c i d abscissa. plotted as The e x p e r i m e n t a l r e s u l t s f a l l on a s t e p - w i s e c u r v e w i t h each o f the f o u r s t e p s c o r r e s p o n d i n g t o a h y d r a t e o f sulfuric acid. The f i r s t s t e p a t 3 0 . 9 N c o r r e s p o n d s t o H S0^- H 0 ; t h e second a t 2 4 . 4 N t o H S 0 ^ 2 H 0 ; t h e t h i r d 2 a a t at • 18 1 7 . 1 N t o H S 0 - 4 H 0 ; t h e f o u r t h a t 5 . 0 1 If t o H S 0 - 20 R \ 0 . 4 4 Z 2 4 I t s h o u l d n o t be a t a l l s u r p r i s i n g t h a t hydrates o f s u l f u r i c a c i d are i n d i c a t e d i n an e l e c t r o l y t i c c e l l . H y d r a t e s o f s u l f u r i c a c i d are known t o e x i s t i n s o l u t i o n . S i n c e the f o r m a t i o n o f a h y d r a t e i n s o l u t i o n i s , a s s o c i a t e d w i t h a c o n s i d e r a b l e f r e e energy change, i t s h o u l d be a s s o c i a t e d w i t h a marked p o t e n t i a l change i n an e l e c t r o l y t i c cell. The p o t e n t i a l s h o u l d v a r y w i t h t h e n a t u r e o f the h y d r a t e formed, hence i t s h o u l d be p o s s i b l e t o d e t e c t the p r e s e n c e o f h y d r a t e s o f s u l f u r i c a c i d i n an e l e c t r o l y t i c c e l l . L e t u s c o n s i d e r the c u r v e shown i n F i g . 4 . We w i l l f i r s t c o n s i d e r the c e l l v o l t a g e a t a v e r y l o w a c i d c o n c e n t r a tion. A t t h i s c o n c e n t r a t i o n we have a d e f i n i t e c e l l p o t e n t i a l , and as we i n c r e a s e the a c i d c o n c e n t r a t i o n we have a decrease i n the o v e r a l l f r e e energy change c a u s i n g t h e p o t e n t i a l t o drop. The drop i s f a i r l y c o n s t a n t up t o a c o n c e n t r a t i o n o f - 5 N and o v e r t h i s range we have the h y d r a t e H S O ^ 2 0 H 0 . z a Beyond t h i s c o n c e n t r a t i o n we do n o t have enough w a t e r present t o form t h i s h y d r a t e so we have a n o t h e r h y d r a t e f o r m i n g , namely ^ 3 0 ^ - 4 ^ 0 . From 5 N t o 1 7 . 1 N t h e s l o p e o f our c u r v e i s c o n s t a n t and o v e r t h i s range we have t h e h y d r a t e H^S0^4H^0. Beyond 1 7 . 1 N we do n o t have enough w a t e r p r e s e n t t o form t h i s h y d r a t e so t h a t we have a change o v e r t o H S O ^ 2 H 0 accompanied t b y a marked change i n p o t e n t i a l . explained i The o t h e r s t e p s c a n be similarly. The p o r t i o n o f t h e t a n t a l u m - p l a t i n u m c u r v e A - B shown i n F i g . 4 was p l o t t e d b y m e a s u r i n g the c e l l p o t e n t i a l s t a r t i n g a t a l o w c o n c e n t r a t i o n o f a c i d and w o r k i n g up t o c o n c e n t r a t i o n o f 17 IT. 19 a The o t h e r end o f t h e c u r v e was p l o t t e d b y m e a s u r i n g the c e l l p o t e n t i a l u s i n g C P . a c i d t h e n w o r k i n g back to 1 8 . 3 N . T h i s gave the c u r v e C - D - E . An a p p a r e n t d i s c r e p a n c y i n the c u r v e i s shown d o t t e d between D and E . To check t h i s p a r t o f the c u r v e t e s t s were c a r r i e d o u t w i t h 1 8 . 3 N , 2 2 . 1 N and 2 4 . 2 N a c i d . A f t e r 20 h o u r s , v a l u e s were o b t a i n e d f a l l i n g on the d o t t e d p o r t i o n o f the curve but a f t e r a n o t h e r 12 h o u r s t h e s e approached t h e solid p o r t i o n o f the c u r v e D - E and remained c o n s t a n t f o r o v e r 5 hours. The c u r v e o b t a i n e d by A s s a l y i s a l s o shown i n F i g . 4 f o r comparison w i t h t h a t o b t a i n e d b y t h e w r i t e r . The e f f i c i e n c y o f the t a n t a l u m r p l a t i n u m c e l l i s c l e a r l y shown t o be much g r e a t e r t h a n t h a t o f A s s a l y s o v e r most o f t h e acid 1 range. The g r e a t drop i n e f f i c i e n c y a t the h i g h a c i d c o n c e n t r a t i o n i s p r o b a b l y due t o the t a n t a l u m d i s s o l v i n g i n the s u l f u r i c a c i d . Other e x p e r i m e n t e r s have shown e v i d e n c e o f t h r e e h y d r a t e s o f s u l f u r i c a c i d b y f r e e z i n g methods. o b t a i n e d the h y d r a t e H S O ^ ^ O ; a Giron^found the Pickering hydrate HgSO^SHaO; and Donk o b t a i n e d c r y s t a l l i n e s u l f u r i c a c i d monohydrate H S O R^O. fe v The f r e e z i n g p o i n t c h a r t o f s u l f u r i c a c i d i s shown i n F i g . 5 . hydrates B , D and G are the e r y o h y d r a t e p o i n t s and C , E and H are t h e m e l t i n g p o i n t s o f the h y d r a t e s R \ S 0 . 4 5 ^ 0 , 4 Hj,S0 . 2 H 0 and R\S0,_- H 0 r e s p e c t i v e l y . + t x From B t o C , D to E 10 o 10 20 3o J Fig.5 O to 70 8° 9o 21 and G to H these r e s p e c t i v e hydrates s o l i d i f y out. The e x i s t e n c e o f H^SO^- 2 0 H 0 i s n o t i n d i c a t e d i n t h e g r a p h b u t t would p r o b a b l y be d e t e c t e d between A and B on c l o s e r examination. Measurements were made o f emf w i t h time f o r concentrations of acid., The measurements f o r t h r e e t r a t i o n s are g i v e n i n T a b l e I I I . several concen- The f i r s t column g i v e s the t i m e , the s e c o n d , t h i r d and f o u r t h g i v e the emf measured w i t h 0.98 N , 27.2 N a i d 35.5 N a c i d r e s p e c t i v e l y . Time-voltage curves f o r these a c i d are shown i n F i g . 6 . concentrations The i n i t i a l v o l t a g e i n a l l c a s e s was v e r y h i g h , d r o p p i n g o f f t o a c o n s t a n t v a l u e a f t e r about 24 hours. A t the b e g i n n i n g an e q u i l i b r i u m - e x i s t e d between the t a n t a l u m m e t a l and the s u l f u r d i o x i d e i n s o l u t i o n b u t as t i m e goes on an o x i d e f i l m forms on the t a n t a l u m and an e q u i l i b r i u m i s s e t up between the t a n t a l u m o x i d e and the sulfur dioxide i i i solution. The i n i t i a l d r o p i n v o l t a g e o c c u r s w h i l e the o x i d e f i l m i s f o r m i n g t h e n the g r a d u a l l y approaches a c o n s t a n t v a l u e . voltage 22 TABLE III E(0.98N) t EC27.2N) E(35.6N) volts mins. volts 0 1.1000 1.0553 1.0240 15 1.0235 0.9352 0.8500 40 0.9500 0.8755 0.7150 1 00 0.9250 0.8503 • 0.6680 1 30 0.9100 0.8255 0.6320 2 00 0.8995 0.8110 0.6100 2 30 0.8900 0.7950 0.5920 3 00 0.8810 0.7825 0.5710 3 30 0.8770 0.7685 0.5530 4 00 0.8650 0.7552 0.5270 5 00 0.8550 0.7490 0.4930 7 00 0.8500 0.7355 0.4730 10 00 0.8308 0.7185 0.4710 15 00 0.8270 0.6978 0.4680 20 00 0.8260 23 30 0.8250 0.6740 0.4635 25 30 0.8249 0.6738 0.4634 urs volts 0.6750 . 0.4637 24 EFFECT OF THE RATE OF SULFUR DIOXIDE AND OXYGEN INTO THE CELL ON THE EMF I n t h e p r e s e n t work a r a t e o f f l o w o f 60 b u b b l e s p e r minute was u s e d f o r b o t h t h e s u l f u r d i o x i d e and o x y g e n . A l t h o u g h t h i s method o f c o n t r o l was o n l y q u a l i t a t i v e i t s e r v e d i t s purpose s i n c e o n l y v o l t a g e was b e i n g s t u d i e d and hot rates o f formation o f a c i d . On i n c r e a s i n g t h e r a t e o f f l o w o f s u l f u r d i o x i d e i n t o t h e c e l l from 60 b u b b l e s p e r minute t o 120 b u b b l e s p e r minute the v o l t a g e i n c r e a s e d from 0.8000 t o 0.8007 several hours. after T h i s v a l u e r e t u r n e d t o 0.8002 on d e c r e a s i n g t h e r a t e b a c k t o 60 b u b b l e s p e r m i n u t e . Decreasing the r a t e t o 30 b u b b l e s p e r minute c u t the emf t o 0.7991 w h i c h r e t u r n e d t o 0.8001 on i n c r e a s i n g the r a t e t o 60 b u b b l e s p e r m i n u t e . On i n c r e a s i n g t h e r a t e o f f l o w o f oxygen i n t o the c e l l from 60 b u b b l e s p e r minute t o 120 b u b b l e s p e r minute t h e v o l t a g e d e c r e a s e d from 0.8000 t o 0 . 7 9 9 0 . On d e c r e a s i n g t h e r a t e t o 60 b u b b l e s p e r minute t h e emf went up t o 0.7997 w h i l e s h u t t i n g o f f the oxygen c o m p l e t e l y , caused t h e emf t o increase slowly to 0.8015. 25 CONCLUSION From the work o f T, C . A s s a l y and the w r i t e r it has been shown t h a t the u t i l i z a t i o n o f the f r e e energy o f s u l f u r d i o x i d e i n the form o f e l e c t r i c a l energy has consider- able p o s s i b i l i t i e s . The p r e s e n t work has been c o n c e n t r a t e d e n t i r e l y on the v o l t a g e d e v e l o p e d i n a s u l f u r dioxide-oxygen c e l l but in f u t u r e the r a t e o f f o r m a t i o n o f s u l f u r i c a c i d i n such a c e l l s h o u l d be s t u d i e d . I f t h i s r a t e c o u l d be made t h e n t h i s c e l l would have d e f i n i t e appreciable p o s s i b i l i t i e s for the p r o d u c t i o n o f s u l f u r i c a c i d and e l e c t r i c a l energy on a commercial scale. 26 REFERENCES.. 1. Chem. and M e t . E n g . , 15,677 (1916). 2. Chem. and M e t . E n g . , 18,178 (1918). 3. T . C . A s s a l y , The B e h a v i o u r o f S u l f u r D i o x i d e , Oxygen, S u l f u r i c A c i d and Water i n an E l e c t r o l y t i c Cell. 4. T r a n s . Am. E l e c t r o c h e m . S o c . , 5 6 , 2 0 1 (1929. 5. L e w i s and R a n d a l l , Thermodynamics, 554 ( 1 9 2 3 ) . 6. P e r r y , Handbook o f Chem. E n g . E d . I I , ' 5 6 3 7. P e r r y , Handbook o f Chem. E n g . E d . I I , 5 5 3 , 8. Z . P h y s i k . Chem., 68,693 9. J . A . C h . S . , 47,945 (1925). 10. J . A . C h . S . , 36,804 (1914). 11. J . A . C h . S . , 40,393 (1918). 12. F i n d l a y , P r a c t i c a l P h y s i c a l C h e m i s t r y , 152 ( 1 9 2 3 ) . 13. Chem. News, 60 ( 6 8 ) . 14. B u l l . S o c . C h i m . , 1913, 1 3 , 1 0 4 9 . 15. Chem. Weekblad, 1 0 , 9 5 6 , A b s t . Am. Chem. S o c . , 1 9 1 4 , 2 , 1 9 2 6 . (1941). (1941). (1910). 27 BIBLIOGRAPHY. 1. A b e g g s Handbuch d e r A n o r g a n i s c h e n Chemie, I V , 2. Adam, N . K . , P h y s i c s and C h e m i s t r y o f 3. C r e i g h t o n and K o c h l e r , E l e c t r o c h e m i s t r y , E d . I I , V o l . 1 1 (Applications). 4. F r e n c h , S . J . , and K a h l e n b e r g , L . , T r a n s , o f Am. E l e c t r o chem. S o c . , 5 4 , 1 6 3 - 1 9 9 ( 1 9 2 8 ) . 5. Getman and D a n i e l s , O u t l i n e s o f P h y s i c a l C h e m i s t r y , 1 (1927), Surfaces, Ed.VII. 6. Glasstone, P h y s i c a l Chemistry. 7. G r e g g , S. J . , A d s o r p t i o n o f Gases b y S o l i d s . 8. J o n e s , H . C , H y d r a t e s i n Aqueous S o l u t i o n . 9. Kreuger, A . C , and K a h l e n b e r g , L . , T r a n s . Am. E l e c t r o chem. S o c , 58,107-152 (1930). 10. Latimer, Oxidation Potentials. 11. L e w i s and R a n d a l l , Thermodynamics and the F r e e E n e r g y o f Chemical Substances. 12. M c B a i n , S. W . , S o r p t i o n o f G a s e s . 13. P e r r y , Handbook o f C h e m i c a l E n g i n e e r i n g , E d . I I . 14. W y l d . W . , S u l f u r i c A c i d and S u l f u r D i o x i d e .
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The sulfur dioxide, oxygen, sulfuric acid cell Leith, James A. 1946
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Title | The sulfur dioxide, oxygen, sulfuric acid cell |
Creator |
Leith, James A. |
Publisher | University of British Columbia |
Date Issued | 1946 |
Description | [No abstract submitted] |
Subject |
Sulfur dioxide |
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Thesis/Dissertation |
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Text |
Language | eng |
Date Available | 2011-11-21 |
Provider | Vancouver : University of British Columbia Library |
Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
IsShownAt | 10.14288/1.0062164 |
URI | http://hdl.handle.net/2429/39194 |
Degree |
Master of Applied Science - MASc |
Program |
Chemistry |
Affiliation |
Science, Faculty of Chemistry, Department of |
Degree Grantor | University of British Columbia |
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UBCV |
Scholarly Level | Graduate |
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http://iiif.library.ubc.ca/presentation/dsp.831.1-0062164/manifest