The Kinetics of the Reaction between Potassium Permanganate and Oxalic Acid Citation Launer, Herbert Franz (1932) The Kinetics of the Reaction between Potassium Permanganate and Oxalic Acid. Master's thesis, California Institute of Technology. doi:10.7907/879d-f064. https://resolver.caltech.edu/CaltechTHESIS:09112024-214755981 Abstract No abstract. Item Type: Thesis (Master's thesis) Subject Keywords: (Chemistry) Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1932 Record Number: CaltechTHESIS:09112024-214755981 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:09112024-214755981 DOI: 10.7907/879d-f064 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16717 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 12 Sep 2024 19:08 Last Modified: 12 Sep 2024 19:12 Thesis Files PDF - Final Version See Usage Policy. 6MB Repository Staff Only: item control page

THE KINETICS OF THE REACTION BETWEEN POTASSIUM PERMANGANATE AND OXALIC ACID Thesis by Herbert F. Launer. In Partial Fulfillment of the Requirements for the Degree of Master of Scj_en~o. ralifornia Institute of Technology, Pasadena, california. - 1932 - THE KINETICS OF THE REACTI ON BET\V-EEN POTASSI UM PERivlAl'JGANATE A ND OXALIC ACID I. by Herbert F . Launer INTRODUCTIOlJ The overall reaction between p erman ganate and oxalic acid is expressed by the equ ati on: 2Mn0 4- + 5H2 c 2 o4 + 6 H+ = 2Mn ++ + 10C0 2 + 8H2 0 rrhe rate of this reaction has been stu died by several :i.nvesti g ators Harcourt and Esson, Phil.Trans.,1866, 201; Schilow, Ber ., 36, 2753 (1903); Skrabal, z. anorg . Chem., 42, 1 (1904). all of whom used an iodimetric method for the analysis of the reaction mixtures. In this paper are presented the results of a new investigation of the reaction between permanganate ions and oxalate ion. A large nu..mber of experiments were mad e on this react j_ on by ai1. i nmroved metho d which show that the mechanism previously sugg ested by Skrabal is not consistent with all of the experimentally found facts. Because of the rathe r complicate d n ature of the reaction the outs t and:i_ng exr)E::rimental r eE;nl ts and theoretical conclusions will , for gre ate r clearness, be s t a te d br:lefly at t h is poi nt. When a solution of pe rmang anate ion is adde d to one of mang anous ion in which acid and ox alate ion are also pres ent a cherry-red solution of a complex ion formed from mang ani c ion and ox alate ion results, whereas in the absence of oxalate ion or - 2 - otl'le.r 8nion capable of forming a complex , a precipitate of mrmganese dioxide is obtained . It will be sho'ivn that the formula of the The rate of the reaction when mang rn1.o u s ion vvas pres ent initially in excess and when the solution we.s in contact vvi th a con st ant gas space was found to be re p resented by the follo ..ving differential equation: .dPc o 2 ( 2) dt The following series of reactions provides a mechani s m that is in accord with eaua tion (2). ~lt<1.04 + 4Mn++ + sw = 5 Mn+++ + 4H2 o Mn+++ + 2C 0~ -- Mn (c o ) 2 4 2 Mn++ + + C204 Mn++ + CO 2 co = 2 + 2 I'fin+++ + co- = Mn+++ CO 2 2 (r apid ) (3 ) (rapid, r eversible) ( 4) (measur~ able) (5 ) ( rapid) (6 ) It will be noted t hat t h e e x ist e nce of an unknow-.D. ion CO 2 is postu- lated in e quation 5 - a matt o r vrh ich is furt:h.e r co n s:i.dered below . Reac tion 3 is to be regard e d in the p resent connection only as the sourc e of tripositive mang anese, the concentration of who se ion (iv1n+++) is determined by the e qui l ibrium c ond itions of reaction 4 . This reac tion a l so invo lves the concentr ation of oxalate ion , wh i ch is itself dependent upon the acidity of the so l ution . The rate of the reaction is then determined by reac tion 5, whose rate should be exn ressed by the e quation : ( 7) By substituting for ( Mn+++) in e quation 7 the expression 1 ( Mn(c o ) )/(c o~) 2 given by the mass -acti on law, there results 2 4 2 k~.c e quation 2, which was found to express the experimental results. 2 Th is mechanism is i n sharp contrast with that of Skr abal, whi ch required that the measureable st ep be the di ssociation of a manganic-oxalate complex, and that the reacti on in which mang anic ion is reduced be rapid, and of third order. \\ I \ \_ ~ J-~-!:' 0,u_ ~~ ti f. . •<-j 1tQ --- ~ ~ METHOD OF EXPERBTENTATION An a pp ar a t u s for 1was1;.r i n g the pressures of c a r bon di - oxide produced wa s constructed snd is shovr.n diag r Bnatically in Fig . 1. Into t h e react ion v es sel we re placed 90 cc. of solution, - 4 - containing all but one of the react8r~ts. Since t he a-o-o aratus is ri g id above the thermostat, a jar, kept overflowing with water from the thermostat may be raised so that C is surro1.mded by water of the desired temperatur e. The stirrer A is so constructed that it not only churns t h e liquid but also forces the vapor phase thro ugh the liquid. The stirrer is connect ed to the system by means of the mercury seal K which is so designed that the ma.,"'Cimum increase in pressure, accom~)anied by a difference in me rcury levels in the seal, will cause a ne g lisj_bly s mall j_ncrease (less than l ;b) in the volume of the vapor phas e. From the buret 10 cc. of _the last reactant were t hen introduced, the stopcock F, was closed, and readings were taken on the water manometer at suitable intervals. The reservoir D contains the water th 2t must be forced u p the manometer tube on the scale Gin order that the hydrost a tic p ressure balance the gas pressure in C, and that the menis cus I return to its initial position . The pressures Pco manometer are proportional 2 of carbo n dioxide as read on the to the number of mols of carbon dioxide evolved in tl}e r eaction , inasmuch as carbon dioxide obe ys Henry 's law at pressures of one tenth atmosphere a...nd inasmuch as the volmne 811.d temperature are essentially constant. The total pressure j_n the system was a l ways in t h e nei ;::)1borhood of one at,nosphere. A series of bla...n.k experiments in which t he rate of stirring ·was varied over wi d e lLmi ts above a certain hi gh va.lue all gave the same c u rve, showing that e quilibrium between the gas and liquid phases was establ ished with s uffi cient rapidity. - 6 - The typical uinduction 11 curve, curve (1), Fig . II, (corres pon ding to expe ri ment (1)) was obt a j_ned when no msngan ous ion vrns initially added. As ind:lcated, point P is coincident with an abr upt color change in the solution . The abrupt simul- taneous chang es of rate and. co lor make it seem re2.sonable that curve (1) from Oto P rep res ents at least three chang es in the oxidation states of mangane se; one from pe rmBnganate to some intermediate state; ano the r, fr om the :'Lnt ermediate state to the manganic state; and the t h ird, from t he mangani c state to the mang anous state. From p oint P to the end , h owever, the curve s eems to re pre- sent only the c han ge from t h e mang an:lc to the mang snous state, the steadily j_ncreasine; ma.nganou s ion con centrat :lon having served to eliminate all stages of m.a.nganese hi gher than the triposi tive one. THE EXISTENCE OF THE M.ANGAlHC OXALATE AND FLUORIDE COMPLEXES In experi ment (2), r epr esented by curve (2), Fi g . II, the manganous io n initially pres ent serve d to reduce the permanganate as rapidly as the lat t er c ould be added, w:i t h the formation of a cherry-red solution. To prove that the cherry-red color is due to tripositive mang anese the f ollowing experiment was performe d. Two e qual p ortions of permar1.ganate solution were treHted vrith an excess of mang anous ion in sli ghtly acid solution. The manganese dioxide pr e ci pitates were each filtered and washed free from manganous ion. One portion was p le.ced in a..n acidified potassium iodide solution and the liberated io dine titrated v:ri th thiosulf ate, of which 20 .10 cc. - 7 - were required. The other por tion was p laced in a so l ution of sulfuric acid and potassiv.L1 oxalate like that of experiment ( 1). The manganese dioxide dissolved rapidly and gave a cherry-red solution, indistinguishable in color from those p reviou sl y observed. Potassium iodide was immediately added and the iodine titrated, using this time 9 .95 cc. of thiosulfate. The tetrap ositive man- ganes e evidently lost one-half of its oxidizing power and was converted, therefore, into the manganic state, the latter being responsible for the color observed above. The reaction that took place was evidently, ( 8) Next, freshly precipitated manganese dioxide was introduced into 8n acj_dified solution of potassj_um fluoride. No mang anese dioxide dissolved until manganous ion was added , whereupon the rapid reaction (9) doubtless took p lace with the subsequent form at ion of a :mangani c fluox•ide complex. THE EFFECT OF ACID, OXAL ATE ION, AND MANGANIC ION ON THE REACTION RATE A comp a rison of curves (2) • and (3), Fig . II, shovvs the effect of acid on the rate. It is to be noted, howe v er , t hat t he co n centr ation of oxalate ion is inversely p1~opo rt ional to the concentrat ion of hydro g en ion, since oxalic acid is weak. The follow- ing experiments show t-hat acid is vvithout :Lnfluence on the rate if the con centrati on of oxalat e ion is fixed: A buffer, cons isting of - 8 - a mixture of a c etic acid and ammonium a c etate, serve d to maintain co n sta:.11t the c oncentration of the oxalate ion . The con c entration of hydrogen ion coul d be v aried four - fold, while that of the oxalate ion remained essentially c onstant . I TABLE The Effe c t of Acid on the Reaction Rate Formula ·weights in 131 2 l iters of solution Experj_ment KiVIn0 4 CH3 COOH K2 c2 o4 CH3 COONH4 MnS0 4 4 5 1 1 6 1 131 262 524 25 25 25 985 985 985 13 13 13 5 4 Ti me Min : se c s 2 6 . 9 . 19 . 24 28 00 10 30 20 00 30 Pressures cm. H2 o 5.1 14 . 2 19 . 7 31 . 2 35 .1 38 .1 Time Min : se c s 2 6 9 19 24 28 .. . . . 00 10 30 20 00 30 6 Pressures cm . H2 o Time Min;se c s 5.1 () 14 . 0 19 . 8 32 . 1 36 . 2 38 . 8 6 9 ::., 19 24 28 Pressures cm . H2 0 00 10 40 20 00 30 5.3 14 . 5 20 . 6 32 . 3 36.5 39 . 2 The rates vary only 1- 27; whj_le the a c idity varies 200%, the concentr at ion of oxalate ion remaining essentially con stant. The results s how that the effect of a c id upon the rate is due solely to it s effect on the concentration of oxalate ion . A s eries of expe riments vvas made in which the a c idity and ioni c strength were maintained constant while t he concentrs.tion of oxalate ion ws.s vo.ried . 1n In preliminary experiments the qumhydrone ele c trode was used to determine the relative prop ortions of sulfuri c ~acid and po tassium oxalate ne c ess a ry to k eep the activity of the hydro gen ion, and h enc e its concentration , constant . Th e p otassium - 9 - sulfate was used to adjust the ionic strength of the solution. In Fig . III the slopes of curve (7) are 2 . 5 times the slopes of curve ( 8) at corresp )n'l:tng points, wb-1.le the concentration of oxalate ion in (8) was 2.5 times that in (7). ( 600 1200 Time in seconds. Formula weights in 1312 liters of solution Experiment KMnO, K,C,O, H,SO, K,SO, MnSO, Activity of H+ 7 8 1 1 50 125 142 164 130 0 13 13 0.0276 .0276 Next, a mixture of potassi-u.111 sulfate, bisulfate and acidoxal.s.te was used to lteep the acidity fixed but to permit the oxalate ion cor..centration to va:ry. In Fig. IV the slope" of curve (9) are twice those of curve (10) and four times those of c1..U've (11) at corres9onding points , the concentration of oxalate ion in (10) and (11) being twice and fo1..1J' times respectively that in (9) . - 10 - ( g= c,:, c,:, c,:, c,:, T"""'I ,---1 T"""'I ...... ~ t:1£0000 ._::sg ~ ~ 2in~ ~ 0 0 <O i:i ,g 0 ., ....."' . cl 0 -; "' ui ,< t g .................. '1:l 0 .... :i: t- t- t- t- ~... 'o..., .....<N 1/) .s., 0 () Q) ~ ;:::l,!IC'l<NC'IC'I c,:, ..... Q) .§ ..c::Q) ·:s0,00<000 ,a:i:<N'°:::'° gE-< E-< .,, 1:4 I 'SI< b.O ~ o! ii; "3 s... 0. 0 = >« ~ r l lQ ,-.-1,..... 0 1:4 0 <N '.I;)l'BM JO ·mo U! 'O;) JO S;}.mss;i.rd ..... = " "'" El ·t: 0,0..-<C'I ............. " [l1 From these results it follows that the rate is inversely proportional to the oxalate ion concentration . From the results of previous investigators, Harcourt and Esson, loc . cit.; Skrabal, loc. cit . and also from the fact that in Fig . IV the slopes of curve (10) are twice those of curve (12), the concentration of oxiclizj_ng agent being in the ratio of two to one, it is evident -~hat the reaction is first order with respect to the oxidizing agent . The concentra- tion of the oxidizing agent is essentially equal to the concentration of the complex manganic oxal ate anion since this complex dis sociates but little, as will be shovm below . - 11 - It is evident that the effe ct of oxalate ion on the rate of reaction ( 5 ) ( s ee Intro ,:.luetiun ) was not (1:i. 1, e ctl y observab l e because of :l_ts effect on the concentration of mang anic ion as shown by equation (4) . Ex-oePiments were next made in which fluoride was added to suppress t hn f orma t ion of the mangani c oxalate comp lex th:rou 0 h t he f ornrn.tj_on of a fluo ri de complex . Th is served to make the concentrat 1on of mangani c ion i ndependent of the c o:r.1ce nt1, a tion of oxal ate ion . Rather crude experiments , the det2J.ls of wh:i_ ch i:dll be t.,; i ven l ater , show that. the mt,mg ani.c f luoride comr lex is nruc h -, ;,ore dissociated than the manganic oxalat e complex . Tho equilibriu.m between the tv.ro complexes rr-u::1.y be re p resented by the fol lowi n,s c hemical equat:1_on . ( I t wi ll be shovm later that the fo1,mulae give n for the comp lexes are p robab1 y correct) . l'.1In (c o ) 2 + 4 p - = L:r_Ji 4 + 2C 2 o4 (10) 1 2 4 Tho mass-action exp ression f or (10) is ( MnF ) ( c 2 o~) 2 oi~-i 4 X (11) c2 o4 \ 2 ) ( F l 4 In equation ( 11), K1O , whi c h is t he ratio of the diss oc:l. at:lon constants of' t}1e two comp lexes, h 8.s a value of approx imate ly 0. 05, and nu-:i.ns ani c ion is to be in the fluoride co!nplex . Thj_s condi. tion was attalned by pl::tc ing the reducing a g ent in deficiency and the oxidizing a gent in suc h excess that chances in t he concentration of the lat ter durin<-:s the f' j_rst t l1.lrd of eac h ex;Je riment r-re.t'e~1e 5 l ig ible. - 12 - In Fig . V the slopes of curve (17) are twice those of curve (19), and the slones of curve (18) are twice those of curve (20) . Also , the slopes of curves (18) and (19) are eaual (at cor- responding points) . Since, as may be seen from the data ,iven under Fig . V, the various concentrations are, at correspondj_ng noints, in the same ratio as the slopes just compared, it follovs that the rate is directly prouortionel to the concentrations of manianic and oxalate ion . This indicates, theref'ore, that the slow sten is the oxidation of oxalate ion by mano;anic ion ( reaction 5) and not the dissociation of the manganic oxalate comulex as assumed by Skrabal . s tJ .!:! 0 ....u 0 "' 20 ~ i 0 ,.___ __.______._ ___._ ____.__ ___,__ _...J 600 1200 Time in seconds. Fig. 5.-The effect of oxalate ion when tripositive manganese is present principally as a complex fluoride. Formula weights in 647 liters of solution Experiment 17 18 19 20 KHC,O, 2 2 1 1 KMnO, 2. 36 (6-fold excess) 1.18 (3-fold excess) 2. 36 (12-fold excess) 1 . 18 (6-fold excess) MnSO, KF KHSO, (NH,)tSO, 26 13 26 13 155 155 155 155 201 201 201 201 65 65 65 65 J - 13 - THE M.f.\NGANIC OXAL A'r E AHD FLUORIDE COii PLEXES Aside :from react i on- rate data it j_s desirable to prove t hat the formul a of the mang sni c oxalate comp lex is Mn(c 2 o4 ) 2. The fol lowing exp eriments were based on t he f act thst if the concentr at i o n of mang ani c ion exc e eds a certain value mang ane.se I n eac h exp eriment was d e t e r mined t h e dioxide will precipit a te . con centr a t ion of ox a l a te or fluoride ion necessary t o p r e vent t h e formatio n of mang anese dioxide fro m a g :I. ven mnount of permang anate , ms.ng anous ion and sulf u ric a cid. Equal p o1"'tions of p ermangan ate we r e a d d e d t o solutions consist i ng of' an excess of aci d a nd of man g m1 ou s 1.on , o.nd of v ar yi n g amounts of p otasshun ox a l a t e s1.,1_c h t hat t he ::.•2.ti o: mols of K2 c2 o4 : mols of tripositive mang anese was 1. 00 , 1, 25 , 1.5, 1.75, 1.875, a nd 2.00. Onl y in t h e last c ase wa s a clear solut ion obt ained , t h us s howing t hat t wo oxalate ions combine w:1. th one manganic i on to f orm t h e complex . With t h is i n f orma tion the follo w~i.. ng e xp erime nts we r e carried out . Ten (10.00) cc. of 0.00762 ~ permanganate (equivalent to 3 9 . 20 cc. thios u l f ate) wer e a d d ed to 6 . 80 cc. of a so l ution con- sisti ng of mang anous i on in exc ess and 0 . 000741 5 mol potass i wn acid oxalate. One dr op more C8.used a preci p itate of mang anese diox ide. Th is soluti on wa s irn.1.1:ed:i. s.tely tr e at e d wi tl1. io d ide :lon an d ac i d . The vo l ume of thiosulfate no w neces sar y was 36.80 cc. wet,te calcul ated t he follo wi n g co n centr a t j_ ons: KBC 2 0 4 rema ini n g - 0 . 04 3 4 0 M Mn III 0.02125 M ti From t h is - 14 0.02125 M Hence , 11 and - - - - 0.00090 M (mca.,ciwu,m.) By analogy to the mang anic oxalate complex the formula Ivln:B1 4 was adopted as being the p robable one. Next , 0.90 cc. of 0.00762 M permanganate were added to 20 cc. of a so lution consist- ing of 0.000824 mol pote.ssium fluoride, 0.0005 mol sulfuric acid, and 0.00101 mol manganous sulfate . A cl.0 8.r solution was obtained which g ave a precipitate of raanga...'1ese dioxide upon the addition of one more drop of permanganate . The concentrations o:f fluoride ion and of the manganic f luoride comp lex were calculate d to be 0.03285 Iv'i and 0.001638 .£i respectively. Since now the concentr8.t:tons of free mang anic ion in bo th this experiment and the oxalate experiment were such th a t a precipi ta.tion of manganese dioxide was bR.rely averted , it may be assumed that the man.garde ion concentration vras the same in both experiments . The concentro..t:i.ons of the two eonmlexes and the fl u ori de and ox2.late ion may , accordi ngl y , be subst:i.tnted in eouation (11) a.rid yield for K 10 the v alue 0 .0 5. These e xueriments indicate that the fornrula of the manganic 2, oxalate com:olex is L'in ( c o ) and r5).ve the m:i. nj_murn ve.lue for the 2 4 (c 2 o4 ) nee es s '., ry to t1ave mangani c man.ganese p resent mainl y as the fluoride coD.p lex . In the f ollowing expe riments, (21) and (22), Fi s . VI, oxalate ion conce nt rat:Lon I'emained nnchange d, ion concentration v aried five - fold . b1.1t the the acid - oxalate The sli5ht difference in rate indJ.cates that it is the oxalate ion, o..rn.3. not tho acid - oxalate ion which forms the complex and which reacts as in equatj_on ( 5). - 15 - t:: 0 ..c: . t:, t:: Q) ~ () ·a .s 8 C'I Q) ..c: ..... .... 0) g .§ <O -,. 1r:----- ... ----- ----- ---- E-< ----- ~ ~ 0 ·1areM JO ·w;, U! io:) JO sa1nssa1d / Curve (21), Fig . VI would represent approximately the rte in experiment (21) if the aci~- oxalate ion were the principal complex-former . THE EFFECT OF IONIC STRLNGTH ON T:-IE RATE In the forer;oing experiments precautions vrnre taken to minimize changes in rate due to changes in the ionic strength . A comparison betv:reen the curves for experiments (22) and (23) , Fig . VI, which differ onl;y in :kmic strength, shows that there is a large positive salt effect on the rate . The change in rate was apnroxi- mately 500% while the chanie in the solubility of carbon dioxide was small , 15%, compared to this . Hhen modified by BrBnsted I s rate h'Y})Othesis the experimentally determined rate equation (2) becomes - 16 - k(Mn(c 2 o4 ) 2) = dt where f 1 , f 2 , and r ( C204) 3 f, • f (18) 2 are the activity coefficients of the manganic oxalate complex, the oxalate ion, and the uniposltive crit:i.cal complex ion respectively. This exp resslon, after cancellation of the activity coefficients of the two singly char g e d ions, evidently requires that the rate increase rapidly with the ionic streng th and thls was found expe rimentally to be the case. The experimental results presented above are al l in accord with the mechan.ism already described. It is believed that the method of exp erimentation used has made possible a more precise determination of the mechanism than was p ossible in the previous studies of the r eaction. THE ROLE OF PEROXIDES I N THE MANGANIC OXALATE REAC TION If the ma..vi.g anic-oxalate reaction be allowed to run to completion in the pres ence of oxyg en t h e resultin[s solutj_on will impart a yellow color to a solution of titanic sulfate. The existence of hydrog en peroxide durins the permanganate titration has been observed Bnd studied by Kolthoff. Kolthoff, Z. anal. Chem., 64, 185 (1924). It is sugg ested here that the hydrogen peroxide arises from an equilibrium between water and a peroxide of carbon, and that this latter results from a combination of the o2 molecule and - 17 - the CO 2 ion in an effort on the p art of both particles to form an electron pair bond fro m t h e i r u n paired electrons. Rat e data show that in the first effective collision between a mang anic ion and an oxalate ion, one electron is removed fro m the latte r . Th is leaves only one electron between the two caI'bon atoms. Since one elec~ron ordinarily does not constitute a stable chemical bond, the carbon atoms part, becoming co 2 and co unpaired electron. 2, a p article with an In a later paper on the effect of oxygen upon this reaction will be presented results in sup port of the above ideas. - 18 - TABLE II RESULTS OF THE RATE MEASUREMENTS Experime.nt (2) Experiment (3) Experiment (7) Experiment (1) Time in Press.CO2 Time in Press.CO2 Time in Press.CO2 Time in Press.CO2 Min:sec in cm.H20 Min:sec in cm.H20 Min;sec in cm.H20 Min:sec in cm.H20 1 2 3 4 5 5 6 6 6 7 15 17 21 26 .. 00 ..• 00 40 50 ..• 20 40 .. 05 30 ..• 55 45 .. 00 10 •• 15 .• 00 0.5 1.2 3.0 8.5 11.1 . 15.1 20.6 27.4 34.8 39.4 40.8 41.0 41.6 42.4 (60.2) 00 45 .... 05 . 30 . 45 3 5 7. 16 18 22 • 26 30 42 45 51 56 . 00 00 .. 15 00 . 30 .. 50 30 . 10 oc, . . . . ... 2.6 5.0 8.1 11.4 14.2 21.6 25.8 28.7 34.1 37.1 (48.0) .. . 00 1 . 20 2 . 30 3 .• 30 4 6 10 14 19 25 31 .. . .. 0 •• 30 1 00 30 1 2 05 05 3 10 4 5 35 7 15 10 50 14 00 ..... .. .. 1.8 3.9 7.0 8.6 11.7 17.1 20.3 0 45 1 • 25 2 25 20 3 4 15 5 30 7 40 8 40 12 20 17 30 6.1 11.2 18.0 22.3 26.2 30.0 34.9 36.8 40.6 43.8 60.2 co (60.2) 00 48.0 (10) 8.1 13.2 18.4 22.3 28.5 33.1 37.2 40.3 43.3 45.8 47.0 .. 00 (20) (21) •• 00 1.9 3.6 4.7 5.8 8.4 13.0 16.7 21.5 26.4 31.0 oO (52) .. 30 30 30 .• 00 ..•• 10 00 4 00 7 30 18 00 22 00 30 00 45 • 00 55 00 (9) (8) 0 • 40 1 30 2 30 3 45 40 4 00 8 10 • 30 12 45 25 18 23 05 2.9 4.2 5.0 9.4 10.4 12.7 15.2 17.1 22.9 · 24.2 26.4 28.4 00 4 6 00 8 00 10 00 17 00 19 • 00 25 30 . . . . . 9.7 13.6 17.7 21.3 32.0 34.5 41.2 55 . . 0 30 00 1 1 30 2 • 05 00 3 10 4 30 5 7 15 00 10 14 00 4.0 7.0 10.2 13.8 19.0 23.5 28.0 32.6 37.5 42.0 (47.0) . .. .. . . . 00 1 . 00 2 . 00 4 . 00 . . . ... 6 00 8 00 10 • 00 17 00 19 • 00 21 00 25 30 00 (22) 2.1 3.8 7.2 10.5 13.3 16.2 24.7 27.2 29.2 33.6 (55) . .... .. .. .. .. 30 00 30 . 05 05 . 15 . 30 00 . 00 (11) 2.6 4.7 6.2 8.3 12.2 16.1 19.7 29.6 35.2 0 1 1 2 • 3 4 5 10 14 00 6 . 00 10 . 00 16 . 00 20 . 00 25 . 00 30 . 00 (47.0) (23) 2.9 4.0 6.2 7.5 9.1 10.9 47 - 19 - The curves g ive n above were dr mvn usj_ng the data presented in this table. The numbers assigned to the curves a~e the srune as those of the corresponding experiments. SUMMARY An apparatus was desi gned for the measurement of rap id reactions in solutions involving even exceedingly small quantities of gase ous product (0.02 millimols) provided either that this gas follow Henry's law or that the deviations therefr om be l{novm. The reaction between tripositive mang anese and oxalate ion has been studied and found, in agreement with the work of previous investi gators, to be an important step in the reaction b e tween permanganate snd oxalic acid. The rate of this reaction was found to be expressible b y the e qu at ion dpC02 =K(Mn(c 2 o4 )j) (c 2 o:) dt when oxalate ion is in excess, and by the e quation when oxalate ion is in deficiency and fluoride ion is present to form a complex with mang anic ion. This led to the adoption of the followirig mechanism. Mn+++ + 2C o Mn(c 2 o4 ) 2 2 Mn+++ + C204 = Mn++ + CO + co2 2 4 Mn+++ + CO2 Mn++ + CO2 (r apid, reversible) (measure!\ble) (rapid) The formula of the manganic oxalate complex ion was found to be - 20 - The influence of the ionic strength on the rate was found to be in accord with that predicted using the Br8nsted hypothesis. An explanation was proposed for the formation of peroxides when the reaction takes place in the presence of oxygen. ** The writer hopes to present the results of further studies upon the subject in an early issue of the Journal of the American Chemical Society.