UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The sulfur dioxide, oxygen, sulfuric acid cell Leith, James A. 1946

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1946_A7 L3 S8.pdf [ 2.44MB ]
Metadata
JSON: 831-1.0062164.json
JSON-LD: 831-1.0062164-ld.json
RDF/XML (Pretty): 831-1.0062164-rdf.xml
RDF/JSON: 831-1.0062164-rdf.json
Turtle: 831-1.0062164-turtle.txt
N-Triples: 831-1.0062164-rdf-ntriples.txt
Original Record: 831-1.0062164-source.json
Full Text
831-1.0062164-fulltext.txt
Citation
831-1.0062164.ris

Full Text

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 .  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0062164/manifest

Comment

Related Items