Definitions of pH Scales.

Bates, Roger G.

doi:10.1021/cr60131a001

Cited by 88 publications

(21 citation statements)

References 93 publications

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“…Each emf value, E, corrected to a partial pressure of 1 atm of hydrogen, can be converted to t he corresponding value of the acidity function, pwH [14], by the equation (1) in which EO is the standard potential of the cell ; F is the faraday, 96,496 abs coulombs per equivalent [15]; R is the gas constant, 8.3144 abs j pel' degree per mole [15]; T is the absolute temperature, to C + 273.16; and f is the activity coefficient on the molal scale. The values of EO and of 2.3026 RTIF in absolute volts are given in table l. The former were obtained by multiplication of thc standard potentials in international volts [16,17] by the conversion factor , l.00033 [181.…”

Section: Methodsmentioning

confidence: 99%

“…If each ionic activity coefficient is expressed by the Huckel equation, the last term of eq 4 become (14) where A and B arc constants at a particular temperature in the water medium [34], a* and {3 are adjustable parameters, and Jl. , the ionic strength, is, for the purpose at hand, negligibly different from the molality of ammonium chloride.…”

Section: Correction For Hydrolysismentioning

confidence: 99%

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Acidic dissociation constant of ammonium ion at 0 to 50 C, and the base strength of ammonia

Bates¹,

Pinching²

1949

J. RES. NATL. BUR. STAN.

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191

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The acidic dissociation of many acids has been studied in detail, but weak bases have genera lly been neglected because of t he experimental difficulties encountered in the investigation of some of their buffer solutions by electromotiye-force methods. These difficulties may arise from volatility of the free base or the existence of extraneous electrode reactions such as the formation of ammine complexes at the s ilver-silver-chloride electrode. In th is study of ammonia, special saturators were used to prevent, insofar as possible, t he removal of ammonia from the solutions by the hydrogen gas. A co rrection was applied for the amou nt of diammine silver complex formed at the sil ver-silver-ch loride electrode, a nd t his silver ion was prevented by mechanical means from reaching the platinum electrodes.With these precautions, the acidic dissociation constant of ammonium ion at 0° to 50° C was determined f rom electromotive-force measurements on 19 b uffer solutions containing equal molalities of ammonia and ammonium chloride. The changes of free e nergy, heat content, entropy, and heat capacity that accompany the dissociation processes in the standard state were derived from the temperatu re coefficients of the acidic dissociation constant of ammonium ion and of the basic dissociation constant of ammonia. The activity coefficient o[ ammonium chloride in equ imolal buffer solutions at 25° C was calcu lated.

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Section: Methodsmentioning

confidence: 99%

Section: Correction For Hydrolysismentioning

confidence: 99%

Acidic dissociation constant of ammonium ion at 0 to 50 C, and the base strength of ammonia

Bates¹,

Pinching²

1949

J. RES. NATL. BUR. STAN.

Self Cite

191

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“…and H designates the total hydrogen-ion species, hydrated or otherwise. This quantity has been called pwH for convenience and to suggest its status as a practical unit of acidity susceptible of exact definition [8]. The pwH is calculated from the emf E by…”

Section: Description Of the Methodsmentioning

confidence: 99%

Dissociation constants of weak bases from electromotive-force measurements of solutions of partially hydrolyzed salts

Bates¹,

Pinching²

1949

J. RES. NATL. BUR. STAN.

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A method for the determination of dissociation constants of weak electrolytes by electromotive-force measuremen ts of solutions of partially hydrolyzed salts of a weak acid and a weak base is described. Although the precision is only half that of the conventional emf m ethod , this procedure has particular advantage in determinin g t he dissociation cons tants of certain bases, for som e of the experim e ntal difficul t ies encountered in adapting the usua l method to solutions containing these bases can be overcome or red uced . The hydrogen-ion concentration of a solution of a salt of this type depends upon the con stants of the weak acid, th e weak base, and water . If two of these are known, th e third can be evaluated by means of e mf m eas ure ments wi t hout the necessity of knowing the exact hydroge n-ion concentration, which is usually difficult to obtain. Hydroge n clectrod es and silver-silver chloride electrodes are used in the cells, and the solut ions are aqueou s mixtures containing the ions of the sa lt and an alkali chloride. The equations for t he calculation of di ssociation constants are deve loped. Th e method was tested by a determination of the basic dissociation constant of tris(hydroxymethyl)aminomcthane at 20 0 , 25 0 , and 30 0 C from three se ri es of meas u reme n ts : (a) by t he con ventio nal e m f m ethod ; (b) by emf studies of the hydrolysis of mixt ures of th e a mine and primary potassium phosphate ; and (c) by emf studies of the h yd rolysis of mixtures of the amine and potassium p-phenolsulfona te. The three determinations were in acceptable agreement. The negative logarithm of the hasic dissociation constant, Pf( b, was found to be 5.946 at 20 0 , 5.920 at 25 0 , and 5.896 at 30 0 C.

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“…An experimental study by Bates et al [6,7] of 0.01 mol Kg -1 H 3 Cit solutions, and application of the equation:…”

Section: Resultsmentioning

confidence: 99%

Acidity function p( a H γ Cl ) as a step to pH assessment

Camões

Lito

2002

Analytical and Bioanalytical Chemistry

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The conventional assignment of pH reference buffer standards, pH(S), is achieved by means of a series of procedures that follow from measurement of Harned cell potentials for an electrolyte solution which is the buffer solution of interest. An intermediate step is assessment of the acidity function p( a(H) gamma(Cl))(0), the extrapolated value of a linear representation of the dependence of p( a(H) gamma(Cl)) on m(Cl) for at least three different molalities, m(Cl), of added alkali chloride (0.005; 0.010; 0.015 mol kg(-1) KCl). This experimental value can be compared with a theoretically expected value calculated from the dissociation constants of the buffer species. Whereas these calculations always give negative slopes for diprotic and triprotic acids and zero slope for monoprotic acids, experimental values with negative or positive slopes can be obtained for well fitting straight lines obtained for buffer solutions with ionic strengths from 0.0025 to 0.144 mol kg(-1). Such disagreement between theoretically and experimentally obtained values introduce an extra source of uncertainty in the establishment of pH(S) and on its traceability chain. In this work examples are presented and discussed for which the discrepancy between expected and experimental values leads to different intercept p( a(H) gamma(Cl))(0).

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Definitions of pH Scales.

Cited by 88 publications

References 93 publications

Acidic dissociation constant of ammonium ion at 0 to 50 C, and the base strength of ammonia

Acidic dissociation constant of ammonium ion at 0 to 50 C, and the base strength of ammonia

Dissociation constants of weak bases from electromotive-force measurements of solutions of partially hydrolyzed salts

Acidity function p( a H γ Cl ) as a step to pH assessment

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