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The vapor pressure of carbon dioxide in equilibrium with mixtures of solutions of potassium carbonate… Melville, John 1923

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The Vapor Pressure o f Carbon Dioxide i n Equilibrium with Mixtures of Solutions of Potassium Carbonate and Potassium Bicarbonate.  by John I l e l v i l l e , B . A . S c .  A T h e s i s s u b m i t t e d f o r t h e Degre e o f UASTER O F APPLIE D SCIENC E i n th e Departmen t of CHELIISTRY  THE UNIVERSIT Y O P BRITIS H COLUMBI A APRIL, 1 9 2 3 .  Table of Contents.  Introduction. Reviev/ of Researches Relatin g t o Thi s Problem . Preparation an d Analysis o f Solutions. Description an d Operatio n o f Static Apparatus . (3 Types) . Results b y Static Methods . Description an d Operation o f Air Saturatio n Me th od s . Summary,  The Yapor Pressure o f Carbon Dioxide i n Equilibrium with Mixtures of Solutions o f Potassium Carbonat e and Potassium Bicarbonate. This problem has a direct bearing upo n the method commercially used for the production of carbon dioxide; according to this method, coke is burned to carbon dioxide, an over excess of air being avoided to ensure th e partial pressure o f the carbon dioxide i n the flue gases being as high as possible. The gases are the n cooled and passed up through a tower, through which potassium carbonat e i s trickling. I n the towers, the normal carbonate i s converted to acid carbonate, according to the equation: K  2 KHG0 Z°°3 * H 2° f °° 2 = 3 The converted carbonat e solutio n from the towers is then boiled  over the cok e burners to effect the revers e change , the carbo n dioxide expelled being drie d and compressed int o cylinders. A knowledge o f the variation in the partial pressure o f the G0? over these solution s will therefore sho w the temperature a t which the maximum yield of OO2 will be obtained * Review of Be searches Relating to this Problem. McCoy (Am . Chem. J., 2? , I903, Page 436) investigated th e "Equilibrium i n the Syste m Composed o f Sodium Carbonate, Sodium Bicarbonate, Carbon Dioxide and Water." H  e state s that the  experimental problem presented was the determination of the composition of the liquid and vapor phases in equilibrium with  2. one another at constant temperature, for various proportions of their constituents. Th e temperature chose n was 25°. Th e method adopted consiste d in shaking 200 or 300 c.c. of the solution of the mixed carbonates , contained in a closed litre bottle, with air, until equilibrium was reached, the whole being kept at constant temperature. A  sample of the gas was  transferred to another vessel and its percentage o f carbon dioxide determined . Th e composition of the solution was determined by analysis. "Th e main series of experiments was made v/ith solutions of bicarbonate an d carbonate of various proportions, and of deci-normal strengt h with respect to sodium. Such solutions of approximately th e desired compositio n were made from separate solution s of bicarbonate an d carbonate, each having the same concentration of sodium. In this work he showed that the equilibrium in the system composed of sodium carbonate, sodium bicarbonate, carbon dioxide and water is governed at constant temperature by the formula 2 x2 0 -  kP (1 - x)  K  in which the symbols have the following significance; x  is the  fraction of the sodiiim in the for m of bicarbonate; 1 - x i s the fraction in the form of carbonate; 0  is the concentration  of the sodium in gram atoms per litre; k  is the solubility  coefficient o f carbon dioxide i n water at the equilibrium temperature; an d P is the partial pressure o f the carbon dioxide.  3. The error in HcCoy's work soerr a to be the assumptio n that the solubilit y o f oarbon dioxide i n his solution i s the same as the solubilit y i n water, and thi s error would becom e more apparent i n solutions of the strength used i n this work, namely 1 and 2 normal. Cameron and Brigg s (J. Phys. Chem., 5, 537, 1901) studied the "Equilibriu m between Carbonates and Bicarbonates in Aqueous Solution." The y drew air through aqueous solution s of the bioarbonates o f sodium, potassium an d magnesium of various oonoentrations, and at four different temperature s and determined by analysis the proportions of oarbonate an d bioarbonate after equilibrium had been reached. McCoy'8 demonstration of the equilibrium existin g between carbonate, bicarbonate, oarbon dioxide and v/ater is applicable t o this study of the vapor pressure o f oarbon dioxide in equilibrium with mixtures of solutions of potassium oarbonate an d bicarbonate* The hydrolytio dissocatio n of potassium bioarbonate is represented by th e equation KECCj •  Hg  O  =  EO  H f  HgCOj  .  This action would naturally b e expected to reach a state of equilibrium by reason of the reverse reaotion . However , the beoarbonate i s itself an acid and can aot upon the free potassium hydroxide, forming water and the normal oarbonate thus : KHCOj f  KO  H -  KgCO  j *  HO  .  4. From the reaction KHCO, + G  H  20 =  KO  H f  l °  3 °  HgOO, .  4  where C., etc., represent the concentrations in gram molecules per litre, we have G3C4  -  K  =  H20 f  (1)  1G1  and from 2H00*  f ZO H  °i  X 2 G0 3  G2  °3  we have -  =1°3  K2G2  (2)  From (1) and (2) 0 ^ K 0,0 3G4 or G-  2c2  ¥  l  L  G2G4 where K is the equilibrium constant for the system under consideration.  %  Preparation and Analysis of Solutions,  The mixed solutions were obtained by first preparing separate solution s of potassium carbonate an d potassium bicarbonate o f equivalent strength with respect to carbonate content and then mixing these separatel y prepared solutions. The solution s were analysed by the method of Winkler as outlined by HcCoy (Loc . cit). "Thi s method consist s in adding in excess a known voliime of standard alkali, free from carbonate, precipitating th e carbonate by addition of barium chloride and finally titrating the excess of alkali with hydrochloric acid using phenolphthalein as indicator" — "Th e net amount of alkali used (tha t is, the whole amount used less that neutralized by acid in the final titration) is a measure o f the carbon dioxide in excess of that existing as normal carbonate. Th e solutions used ranged from 1 to 2.5 normal with respect to carbonate. The determination of the vapor pressure o f these solutions was carried out by two methods: (1 ) a static method (j5 modifications, described below) which gave the combined vapor pressure o f carbon dioxide and water and (2) a n air saturation method, which gave the vapor pressures of carbon dioxide and water separately . A n attempt was also made to determine the separate partial pressures of carbon dioxide and water by isolating and analyzing a sample of the gas in equilibrium with the solution. Th e addition of the separate values obtained by  6.  t h i s l a t t e r metho d o r b y th e a i r s a t u r a t i o n metho d t o giv e th e same valu e a s obtaine d b y th e s t a t i c method , fo r correspondin g t e m p e r a t u r e s shoul d serv e a s a chec k o n th e work .  D e s c r i p t i o n an d Operatio n o f S t a t i c Apparatus . The s o l u t i o n t o b e i n v e s t i g a t e d wa s containe d i n th e f l a s k A ( P l a t e 1 ) whic h wa s containe d i n a wate r bat h B l Connection wa s mad e b y mean s o f th e three-wa y stop-cock , 3 , w i t h th e Manometer , M . Change s i n p r e s s u r e , brough t abou t b y varying th e temperatur e o f th e b a t h , wer e rea d of f fro m th e manometer b y mean s o f a cathetomete r o r a metr e s t i c k place d behind th e manometer . I  t wa s foun d t h a t whe n t h e f l a s k , A ,  was connecte d d i r e c t l y t o th e manometer , withou t th e f l a s k F, t h e r e wa s excessiv e condensatio n i n th e connectin g t u b e s . The apparatu s wa s cleaned , d r i e d an d the n evacuate d b y an oil-pump , th e three-wa y stop-cock , S , bein g i n p o s i t i o n ( 1 ) . The ope n v e r t i c a l ar m o f th e three-wa y stop-coc k wa s the n f i l l e d wit h s o l u t i o n an d th e stop-coc k turne d t o p o s i t i o n (2 ) so t h a t th e s o l u t i o n ra n i n t o f l a s k A . Th  e stop-coc k wa s  turned bac k t o p o s i t i o n ( l ) befor e a l l th e s o l u t i o n ha d ru n ou t of th e ope n ar m s o t h a t n o a i r e n t e r e d t h e a p p a r a t u s . Thi  s  procedure o f f i l l i n g t h e ope n ar m wit h s o l u t i o n an d allowin g i t to tu n i n t o f l a s k A was r e p e a t e d u n t i l t h e r e wa s approximatel y 100 c . c . o f s o l u t i o n i n Flas k A . Th  e bat h wa s t h e n heate d  over a rang e o f fro m 10 ° C . t o 9.5 ° C . an d th e p r e s s u r e s note d  FLRTE T  7. on the manometer. I  n order to make sure that equilibrium was  reached between the vapor an d solution, the temperature was raised slowl y and maintained a t the various temperatures for several minutes before the pressure correspondin g to that temperature v/as read off.  Results by Static IJethod.  The curve s of vapor pressures on a temperature base for three solution s are show n in Plates 11, 111 and IV, the data from which they were plotted being given in Table 1. To prevent condensation in the connection between the solution and manometer of the static apparatus, the stationary manometer was replaced by one having one arm maintained at constant level in the bath by raising or lowering the open arm. However with th e solution at 120° C (paraffin bath), thi s necessitated a mercury column of approximately 2. 5 metres high so that reliable dat a could not easily be obtained.  gable 1, Solution No. 1, Wo . 2, No . 3, 1.38 Hormal, I.3 4 Formal, 2.2 3 Formal. Tenrpj Pressur 8 12  Jl 16  18 20 21 23 24 25 28 32 33 35 37 40 43 45 46 48 50 32 33 55 56 57 60 62  U 70 72 75 77 80 81 82  £843 Si 22 88  90 91 92 93 94  e in mm: Pressur _ -  15.0  e in mm. Pressur  12 16  -  17.4 18.2 -  26.6 -  29.8 -  26 31  74.4 91.4  78 85  -  58.4 a*  -  -  112.8 -  140.0  -  97 112  _  m  428.0  m  _  46.4 53.0 59.2 _  -  _  78.8 83.0 91.2 98.6 —  113.0 -  387** 439 455 491 513 536 549 567  -  279.6 320.0 350.0 359.6 378.8  w  34.6 40.6  *• -  -  212.8  M  _  29.8  -  176.4  m  23.6  _ -  139 149 167 196 212 235 263 292 325 338 351 363  -  —  M  38 41 45 51 58 67  48.8  „  m  20  e in mm;  —  123.0 136.6 151.8 172.1 196.4 216.6 239.2 267.4 297.6 332.0 364.0 382.4 412.6 _  „  _ — — _ —  PLFITt 77  1  4  soo  4O0  /ofaf fapor Prendre of •/Y''Ae.c£ Ca.r donccfe. So/cci  1  Ay S/snJi/e. /yTxryo^rj  So/ution- /i<  JSOO  VMU  €7^ ^  5 /form <*/ .  / //  zoo  /  /oo ynmm* GT.  mefcu.ro  _ ^ '•n degrees C.  0 Co  s  a/  < »o  /PLfiTb nt \ \ i  .  i  son  i 400  Tofa./ 1/a.oor Preau-rc of f*f/Kcci Carbonate. So/u.ti<. dy S//r?p/e Wano/nete-r.  >a.  an /•£>#-/Yof~sr>a-/-  300  ZOO  / . /OO  rretiu-re jr> m/i? of  •  tyercuiy  ""> degrees C.  -.r^A^  f*  •> 6  )<  30 A  3o  PLFITL ,/ v i  i !  1L  .  soo  4O0  7 5 / W fa? or Pressor* of •rf/xCci Ca.rhona.fc  . 3o/aTio  Au S>mp/e /vfan  o/mefer.  So/u. t,on. ZZ3  300  /form  a  n.  i /.  f  ZOO /  I  r1  ...  f /OJ)  ^  /n msn. of Trercartf  1  Tenr,^era.turt ZO \t*» Ueortes Ci  40  i  io  io  /oO  -  9. The determination o f the total vapor pressure of the solutions was then attempted l>y means of the isoteniscope or differential manometer (Plat e V ). Thi s consists of two glass bulbs of 200 c.c. capacity provided with stop-cocks and connected through a manometer. Th e apparatus is evacuated through the oj)en arms, the solution run into one bulb and distilled water into the other bulb. Th e open arms are then sealed off below the stop-cocks. Th e apparatus is immersed in an oil bath provided with a glass window so that the manometer can be observed. Th e differences in the vapor pressures of the pure water and the solution , as the bath is heated, are read off from the manometer by means of a cathetometer and scale attached immediately behind the manometer. Th e vapor pressure of water and the density of the mercuty column at different temperatures are obtained from tables. The curves of vapor pressures on a temperature bas e for two solutions obtained by this method are shown in Plates Vll and Vlll, the data from which they were plotted being given in Table II.  —  JHLATZM.  Table 1 1 . S o l u t i o n 1 . Norma l w i t h r e s p e c t t o X . Temp. °G 13 27 ••7  70 81 100  no  125 145  133 158 160 165 167 169  Uanometer Difference  + 1.54 c™ 1.48 1.68 2.11 2.82 3.41 3.76 4.36 5.40 3.50 3.11 2.40 .84 .37 .03  Corrected Difference  +-1, 339 1, 479 1, 665 2, 085 78o 2,330 J. 670 3- 260 4, 250 3 3. 410 3, 030 2,333 815 33? 029  C f* v  Differanee X V . P . o f H20. Ha <A O» C ,  2.806 4.126 9.372 25.416 39.731 79.350 112.207 178.948 317.805 412.27 444.98 467.50 528.27 554.50 581.92  Solution 1.5 Normal with respect to 19 31 46 34 72  p86 *2 98  102 109 117 120 123 126 130 132 133 137 139 140  -.31 -.62 -.33 -.16 +-.22 +-.91 + 1.3 9 1.33 1.53 1.72 2.29 3.06 4.45 5.44 6.52 7.75 8.02 7.96 6.48 4.25 3.34  -.508 - .61 7 _ .34 7 -.139 + .21 8 + .93 7 +I.565 1.524 1.512 I.689 2.250 2.933 4.365 3.320 6.360 7.560 7.840 7.760 6.315 4.145 3.455  1.124 2.720 7.166 11.03 8 25.648 35.030 46.612 54.071 72.225 83.290 106.215 138.421 153.493 169.216  186.195 210.588 223.343 243.13 255.74 268.29 275.22  PL fire ss  PL/9T£ ¥7' 1  -  1 I 1  ' i 1  i 1  zoo4tflm.  7o/"a/ l / a ^ o / PresSou-* a/Sf/%.ccL C(XrA>c,na.fe. by J  zzs  S'o/cc/'/  /  on.  So/e.nr scope.  5o/u.f, on.  /'S~/forma./  34f~,  /  1  /  /  / /SO T&trr)  f  / 75  /  Ifi+rr,  ~  Pre Hurt  in cm. ofrnercury  femferafccrt 30  <o  09  on  to /  . so  11.  Description and Operation of Air Saturation Apparatus* The solution was contained in the towers I (Plate IX) filled with glass beads and immersed in the constant temperature water bath. (Belo w 30° and above 70°, difficulty was experienced in keeping the temperature constan t to within 1° since the heating was effected by means of a Bunsen burner and no temperature regulato r was available). Ai  r was drawn through  the solution by means of the aspirator A and the water vapor absorbed in U-tubes (1 ) and (2) containing concentrate d sulphuric acid on pumice ston e and the carbon dioxide absorbe d in the Griessler bulb G, containing concentrated (40^ ) ICO H solution and in U-tube (3) . Betwee  n the towers, U-tubes,  Giessler and aspirator, close rubber connections were used and the cork of the aspirator was sealed in with paraffin. Whe n closed at the inlet end of U-tube (1 ) and exit from the aspirator, the system did not leak appreciably with a pressure of 60 num. of mercury less than atmospheric i n the aspirator. In all the runs, the pressure in the aspirator was never more than 55 m.m. of mercury less than atmospheric s o that no error could have entered in the measurement of the volume o f the air which was determined from the volume o f water run out. This air saturation method is essentially similar to that used by Wiedermann, Stelzner and Uiedershulte (Verh . phys. Ges., 3, 159) an d by G.P. Baxter (J. Am. Chem. S o c, 2? , 1907, page 127) i n the determination of the vapor pressure of iodine,  r~  PL/iTL *F»  12. and by Schumb (J. Am. Ghem. S o c, 43 , 1?23, page 342) i n the determination of the dissociation pressures of certain salt hydrates. Schumb's method (loc. cit) consiste d in drawing a measured amount o f dry air, free from carbon dioxide, through an intimate mixture of the pair of hydrates and collecting the water vapor thus taken up by the air in weighed U-tubes containing phosphorus pentoxide. Th e normal length of his runs was 18 hours during which time 6 to 8 litres of air were aspirated. Als o th e temperature o f his system never varied more than two degrees from room temperature s o that he would not encounter the condensation difficulties which developed in this work. Baxter's method (loc . cit) wa s to pass a measured volume of pure dr y air, first over the pure iodine, and then into a solution of sodium sulphite t o absorb the volatilized iodine. From this sulphite solutio n the iodine was precipitated as silver iodide, which was collected and weighed. Hi s method of calculating the vapor pressure o f the iodine from the v/eight of silver iodide was applied to this problem as given in the following example. Increase in U-tub e (l ) U-tub e (2 ) Giessle Weight of .178  3 gm. .002 ?  gm. .027  r U-tub e (3 )  1 gm. .00? 2 gm.  .1814 gm. HO .036 3 gm. CO„ 2 2 Temp, of bath 6 0 Baromete r 73 ? m.m. 0 Temp, of air I8.3 -4 3 m.m. in Aspirator.  13. Volume o f a i r 130 3 c . c . -2  9 num . i n Tower .  Vapor t e n s i o n o f wate r a t 18.5 ° i s 15. 8 m.m . Therefore th e a i r i n th e A s p i r a t o r wa s unde r a p r e s s u r e o f 759 -  4 3 - 15. 8 o r 698. 2 m.m .  The volum e whic h t h a t a i r woul d occup y i n th e tower s i s 1305 x m  x  6^8. 2=  Wtt ~7To  ~  142  7 c.c .  .1814 gm . H2 O a t t h e t e m p , an d p r e s s u r e i n t h e t o w e r s would occup y . 1 8 1  4x  2240 0 x 33 3 x  T 8 ~ TT3  76  7J0  0-  286.  2 c.c .  ""  .0363 gm . G O a t t h e t e m p , an d p r e s s u r e i n t h e t o w e r s would occup y .036  0 x ^3^  3 x 2240 4T" "2"7  x 76 J 1JU  0-  23.  T o t a l : 1736.  Partial pressur e o f H O -  286.  2x  73  P a r t i a l P r e s s u r e o f G0 2=  23.  3x  73= 0  d  1736.  7  0-  120.  9.9  3 c.c . 7 c.c .  3 m.m .  m.m .  T o t a l : 130.  2 m.m .  Total b y a i r s a t u r a t i o n metho d : 140.  0 m.m .  Such c o n s i s t e n t l y lo w r e s u l t s b y th e a i r s a t u r a t i o n method, a s i n th e abov e example , l e d t o th e conclusio n t h a t t h e r e wa s condensatio n o f wate r befor e a b s o r p t i o n . I  f suc h wer e  the c a s e , i t woul d b e reasonabl e t o assum e t h a t wit h a l a r g e volume o f a i r a s p i r a t e d , th e amoun t o f w a t e r remainin g unabsorb ed woul d becom e a n e g l i g i b l e f r a c t i o n o f th e t o t a l q u a n t i t y o f w a t e r . Consequentl  y a l a r g e numbe r o f r u n s wer e mad e eac h  14, extending ove r a p e r i o d o f 9 t o 1 2 hour s i n whic h tim e 3 t o 3 l i t r e s o f a i r wer e a s p i r a t e d . I  t wa s foun d howeve r t h a t , eve n  w i t h t h i s p r e c a u t i o n th e a i r s a t u r a t i o n metho d s t i l l gav e r e s u l t s c o n s i d e r a b l y lowe r tha n th e t o t a l obtaine d b y th e s t a t i c method. The followin g f i g u r e s fo r t h r e e run s sho w th e wid e v a r i a t i o n i n th e weight s o f CO Temp, o f Bath . 60  ?  an d wate r vapo r absorbed , ° 6c  r 60  Vol. o f a i r a s p i r a t e d 320  0 c . c . 32.5.  5 c . c . 328 0 c . c .  Wt. o f H 20 absorbe d .136  4 gm . .421  0 gm . .2.51 9 gm .  Wt. o f C0  3 gm . .130  8 gm . .093 8  2  absorbe d .128  P a r t i a l P r e s s u r e o f H^O . '47, •"  "  00  2 - 13,  6 mm , 113.7mm 9 " 14.  7"  Total b y a i r s a t u r a t i o n . 63.  3 " 130.  4"  Total b y s t a t i c . I49.  O " 149.  0u  °  .  Boswell an d Gantel o (Can . Gh . an d Mat. , Yol . 7 1 , Ho.3 , May 1922 ) a l s o ha d troubl e w i t h t h i s metho d an d conclude d t h a t even w i t h a l l p o s s i b l e car e "th e bubblin g metho d i s s t i l l sub j e c t t o a n e r r o r s o l a r g e an d u n c e r t a i n a s t o mak e i t e n t i r e l y untrustworthy." Attempts wer e t h e n mad e t o determin e th e p a r t i a l p r e s s u r e of t h e carbo n dioxid e b y a d i f f e r e n t method , u s i n g apparatu s shown i n P l a t e X . Thi s c o n s i s t e d o f a f l a s k connecte d b y mean s of a wire d rubbe r connectio n t o a tub e provide d w i t h a stop-coc k a t eac h en d o f th e enlarge d p o r t i o n . Th  e apparatu s wa s evacuat -  ed, the n s o l u t i o n ru n i n t o th e f l a s k , stop-cock s bein g open .  ?*£.J9T£ U>  £  15. The apparatu s wa s the n immerse d i n a constan t temperatur e bat h for 3 t o 4 hour s wit h intermitten t a g i t a t i o n , afte r whic h tim e stop-cock S wa s closed , thu s i s o l a t i n g a sampl e o f th e vapo r in equilibriu m wit h th e solutio n a t tha t temperature . O n cooling, t h i s sampl e o f ga s wa s analyze d b y standar d method s for i t s carbo n dioxid e content . Owing t o th e d i f f i c u l t y i n keeping ' th e stop-cock s t i g h t in eve n a moderatel y war m bat h an d i n closin g stop-coc k 3 without exposin g th e connections , thu s disturbin g th e e q u i l i b rium, r e l i a b l e dat a coul d no t b e obtaine d b y t h i s method .  16.  Summary*  (1) Stati c methods have been described for obtainin g the total vapor pressure o f carbonate solutions, and results by simple and differential manometer methods have been tabulated and plotted.  (2) Ai r saturatio n methods, for determining separatel y the partial pressures of carbon dioxide an d water vapor from mixed carbonate an d bicarbonate solutions have been described and difficultie s in their operation pointedout.  In conclusion I desire to express my indebtedness to the Advisory Research Council and to Dr. E.H. Archibald for encouragement an d assistance.  


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