The Ionization Constant of Formic Acid from 0 to 60°<sup>1</sup>

Harned, Herbert S.; Embree, Norris D.

doi:10.1021/ja01320a010

Cited by 92 publications

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“…The last two measurements of experiments 1 and 4, when more than 95 percent of the salt had been neutralized, have not been included in the average. The averages of all the pK' values derived from these experiments agree very well (0.001 unit) with the best values of pK for these two acids given in the literature [10,11]. pH values of buffer solutions with an accuracy of 0.01 to 0.02 unit.…”

Section: --------------------------------------------------------supporting

confidence: 85%

“…For formic aeid, pK' at an ionic strength of 0.1 is 0.009 unit higher than the value at zero concentration [10], whereas the measurements of Harned and Ehlers [11] indicate that the corresponding increase in pK' for acetic acid is even smaller, or about 0.005 unit. The observed difference between pK' at the two ionic strengths (0.1 and 0.077) used here should accordingly be about 0.002 unit, or less than the error of the measurement.…”

Section: Dissociation C Onstantsmentioning

confidence: 78%

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Dissociation constants and pH-titration curves at constant ionic strength from electrometric titrations in cells without liquid junction: titrations of formic acid and acetic acid

Bates¹,

Siegel²,

Acree³

1943

J. RES. NATL. BUR. STAN.

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An improved method for obtaining the titration curves of monobasic acids is outlined. The sample, 0.005 mole of the sodium salt of the weak acid, is dissolver! in 100 ml of a 0.05-m solution of sodium chloride and titrated electrometrically with an acid-salt mixture in a hydrogen-silver-chloride cell without liquid junction.The acid-salt mixture has the composition: nitric acid, 0.1 m; pot assium nitrate, 0.05 m; sodium chloride, 0.05 m. The titration therefor e is performed in a. medium of constant chloride concentration and of practically unchanging ionicstr ength (1'=0.1) . The calculations of pH values and of dissociation constants from the emf values are outlined . The tit ration curves and dissociation constants of form ic acid and of acetic acid at 25 0 C were obtained by this method. The pK values (negative logarit hms of the d issociation constants) were found to be 3.742 and 4. 754, respectively.

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Section: --------------------------------------------------------supporting

confidence: 85%

Section: Dissociation C Onstantsmentioning

confidence: 78%

Dissociation constants and pH-titration curves at constant ionic strength from electrometric titrations in cells without liquid junction: titrations of formic acid and acetic acid

Bates¹,

Siegel²,

Acree³

1943

J. RES. NATL. BUR. STAN.

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“…100 (0. 100) .111 -log Kl at 25°, to obtain -log K l at the other 12 temperatures . Th e following equat,ion, the cons tants of which were determined by the method of least squares, represents the "observed" log K I from 0° to 60° with an average deviation of ± 0.0005:…”

Section: The Temperature Coefficient Of Log Klmentioning

confidence: 99%

First dissociation constant of phosphoric acid from 0-degrees-C to 60-degrees-C; Limitations of the electromotive force method for moderately strong acids

Bates¹

1951

J. RES. NATL. BUR. STAN.

115

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An accurate det.ermination by t he electro motive-force m ethod of t he di ssoc iat ion constant of an acid as strong as t he first ac idi c g roup of phospho ric acid r eq uires t hat the hydrogen-ion concen t rat ion be estab li s hed wi t h greater accuracy than is usually attainable. The un cer tain quantity is t he activ ity coe ffi cie nt of hydrochloric acid in the particular mixture und e r st ud y. It is shown th at the calculation of this coefficient by t he DebyeHi.ickel eq uat ion , which afford s a n adequate estimate of the sma ll hydroge n-ion co rrection in buffer solut io ns com posed of weak acids, fa il s to y ield the desired accuracy for mixtures in whi ch the acid is dissocia ted to an a pprec iable exte nt. In order to determine t he common logari thm of t he first di ssociation co ns tan t of phos phoric acid wi t h an acc uracy be lie ved to be ± 0 .005 uni t, the hydrogen-io n concentra tion of some of t he buffer mixtlll'es s tud ied was kept at lo w levels by use of a la rge excess of potassium dihydrogen phos phate. Ot her so lu tions contain ed formic acid in stead of hyd roc hlo ric acid , the reby lowerin g the hyd rogen-ion concentration st ill further. In addit ion , p a r t icu lar attention was g ive n to a cho ice of reaso nable valu es fo r t he activity coefficient used to es t im ate t he hyd roge n-io n cOl'J'ection .By t hese m eans t he first di ssociatio n con stant, Ie , of phosphoric acid was calculated from e mf measure ments of 7] phosphate buffer sol ut io ns, togeth er ",ith supplementary data from th e lit e rature foJ' 18 add itional so lu tio n . The result from 0° to 60° C is g iven by -log [(1 = 79 ; ; 31 __ 1.5535 + 0.013486 T , \\'h ere T is th e temperat ure in °IC Th e changes of heat content, e ntl'Op.v , a lld heat capac it y foJ' thc di ssociat ion of 1 mo le of aqueous phospho ri c acid in t he sta nd a rd state were fOlilid to be -7,650 j, -66.8 j deg-I , and -154 j c1 eg-l , res pective ly , at 25° C. Introdu ctionExperience has proved Lhat Lhe electromo tiveforce m ethod is well sui ted to the accura te determination of the dissociation constants of many weak acids and bases in aqueous solu tion . However, it is not gen erally r ecogniz ed that tbe accuracy obtainable by this method diminishes with increasing strength of the acid or base. I'Yh en approximately 10 percent or more of a weak acid is dissociated in solution, th e uncertain ty in establi shing th e tru e concen trations of the ionic and molecular species becom es so large that an exact determination of the dissociation con stant is no 'longer possible.Som e years ago th e author undertook to m easure the electromo tive force of a series of cells of the type Pt; H 2 (g, 1 atm) , KH2P04 (xm), H CI (m) AgCI; Ag (Cell 1) where m is molality, in an attemp t Lo extend the investigation of N ims [l jl Lo oLh er temperatures and buffer ratios. It was found to b e impossible to obtain an accura te value for th e first dissociation constant of phosphoric acid by analysis of t h e data for mixtur...

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“…This suggests that this stage also occurs by the conventional mechanism, as shown in eq. [5]. These mechanistic assignments are reinforced by the fact that examination of the proton nmr spectrum of the reaction mixture midway through the second stage of hydrolysis of 2,3-dimethoxy-1,3-butadiene conducted in D20 solution showed only one deuterium atom in the methyl group of 3-methoxy-3-buten-2-one and no deuterium incorporation in its vinyl group.…”

Section: Reaction Mechanismmentioning

confidence: 98%

Vinyl ether hydrolysis. XVIII. The two-stage reaction of 2,3-dimethoxy-1,3-butadiene

Kresge¹,

Yin²

1987

Can. J. Chem.

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A. JERRY KRESGE and YA YIN. Can. J. Chem. 65, 1753Chem. 65, (1987.The kinetics of acid-catalyzed hydrolysis of 2,3-dimethoxy-l,3-butadiene (1) to 3-methoxy-3-buten-2-one (2) and the subsequent lo4 times slower conversion of the latter to biacetyl (3):O M e O M e 0 were studied in aqueous solution at 25OC. Both stages of this process give substantial hydrogen ion isotope effects, kH+/kD+ = 2.95 for Stage 1 and kH+/k,+ = 1.83 for Stage 11, and Stage I shows general acid catalysis in formic and acetic acid buffers; both stages are therefore assigned the conventional mechanism for vinyl ether hydrolysis involving rate-determining proton transfer from catalyzing acid to substrate. The second vinyl ether group of the initial substrate (1) is found to have only a slight (3-fold)accelerative effect on the reactivity of the first group, but the acetyl substituent present in the intermediate 2 decreases its reactivity by a factor of lo4; the latter appears to be due largely to the electron-withdrawing inductive effect of acetyl, with little or no influence from a countervailing electron-supplying resonance effect.A. JERRY KRESGE et YA YIN. Can. J. Chem. 65, 1753Chem. 65, (1987.Optrant a 25°C et dans des solutions aqueuses, on a dCtexmint la cinktique de l'hydrolyse acido-catalyske du dimtthoxy-2,3 butadikne-1,3 (I) en mtthoxy-3 buthe-3 one-2 (2) et de la transformation subsCquente de ce dernier, qui est lo4 fois plus lente que la rCaction prtckdente, en biacCtyle (3). Pour chacune des ttapes, on observe des effets isotopiques cinitiques de l'ion O M e be expected to occur in separate stages proceeding at rather different rates. This follows from the fact that the conventional mechanism for vinyl ether hydrolysis involves rate-determining proton transfer from a catalyzing acid to the substrate in a step that generates a carbocation intermediate (I), and a-acyl sub-We wish to report that we have examined the kinetics of hydrolysis of 2,3-dimethoxy-1,3-butadiene and have found this to be the case. Our results provide a quantitative estimate of this a-acetyl effect on carbocation stability, a subject of some current interest (2), and also give information on the effect of one vinyl ether group in 2,3-dimethoxy-1,3-butadiene on the reactivity of the other. Results Reaction identijication2,3-Dimethoxy-l,3-butadiene has a strong uv absorption band For personal use only.

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The Ionization Constant of Formic Acid from 0 to 60°¹

Cited by 92 publications

References 0 publications

Dissociation constants and pH-titration curves at constant ionic strength from electrometric titrations in cells without liquid junction: titrations of formic acid and acetic acid

Dissociation constants and pH-titration curves at constant ionic strength from electrometric titrations in cells without liquid junction: titrations of formic acid and acetic acid

First dissociation constant of phosphoric acid from 0-degrees-C to 60-degrees-C; Limitations of the electromotive force method for moderately strong acids

Vinyl ether hydrolysis. XVIII. The two-stage reaction of 2,3-dimethoxy-1,3-butadiene

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The Ionization Constant of Formic Acid from 0 to 60°1

Cited by 92 publications

References 0 publications

Dissociation constants and pH-titration curves at constant ionic strength from electrometric titrations in cells without liquid junction: titrations of formic acid and acetic acid

Dissociation constants and pH-titration curves at constant ionic strength from electrometric titrations in cells without liquid junction: titrations of formic acid and acetic acid

First dissociation constant of phosphoric acid from 0-degrees-C to 60-degrees-C; Limitations of the electromotive force method for moderately strong acids

Vinyl ether hydrolysis. XVIII. The two-stage reaction of 2,3-dimethoxy-1,3-butadiene

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The Ionization Constant of Formic Acid from 0 to 60°¹