Calculated equivalence volume in potentiometric acid-base titrations

Summary Using a pH meter, a motorized burette and a programmable pocket calculator potentiometric acidbase titrations may be carried out with a high degree of precision, a high degree of accuracy and in a time comparable to the time needed to perform a titration with a visual indicator. With the exception of the lowest concentration of the weak acid a precision higher than 0.01 ml of the reagens is easily obtainable, whereas the accuracy may be as high as 0.1 %. The method is suitable over a wide range of concentrations of either strong or weak acids.

---

Berechnetes Äquivalenzvolumen bei potentiometrischen Säure-Base-Titrationen

Zusammenfassung Mit Hilfe eines pH-Meßgeräts, einer Motorbürette und einem programmierbaren Taschenrechner können potentiometrische Säure-Base-Titrationen mit hoher Reproduzierbarkeit und Richtigkeit in einer mit der Verwendung von visuellen Indicatoren vergleichbaren Zeit durchgeführt werden. Mit Ausnahme der niedrigsten Konzentration einer schwachen Säure wurde eine Reproduzierbarkeit von besser als 0,01 ml und eine Richtigkeit von 0,1 % erhalten. Das Verfahren ist für einen weiten Konzentrationsbereich von starken und schwachen Säuren geeignet.

     

Method for determination of the equivalence point in potentiometric titrations

A method is developed for calculating the end-point and the ionization constant in a potentiometric titration. The influence of dilution is studied. The method is compared with the procedure of KOLTHOFF and that of HAHN.     

Calculated equivalence volume in complexometric titrations

Summary Using a digital pH-meter, a motorized burette and a programmable pocket calculator, complexometric titrations were executed with a high degree of precision, a high degree of accuracy and in a time comparable to the one needed for performing a titration with a visual indicator. If a suitable sensing electrode is at hand, concentrations as low as 0.001 M may be analyzed without difficulties.

---

Berechnetes Äquivalenzvolumen bei komplexometrischen Titrationen

Zusammenfassung Mit Hilfe eines Digital-pH-Meßge-räts, einer Motorbürette und einem programmierbaren Taschenrechner konnten komplexometrische Titrationen mit hoher Präzision und Genauigkeit in einer der visuellen Indikation vergleichbaren Zeit durchgeführt werden. Mit einer geeigneten Meßelektrode können Konzentration bis herab zu 0,001 M ohne Schwierigkeiten erfaßt werden.

     

Calculated equivalence volume in precipitation titrations

Summary Using a digital pH meter, a motorized burette and a programmable pocket calculator, precipitation titrations may be carried out with a high degree of accuracy and in a time comparable to the time needed to perform a titration with a visual indicator. Not too diluted solutions (not below 0.001 M) may be analyzed with a 95% confidence interval of less than ±0.01 ml, whereas the accuracy amounted to 0.1%.

---

Berechnetes Äquivalenzvolumen bei Fällungstitrationen

Zusammenfassung Mit Hilfe eines Digital-pH-Meßgeräts, einer Motorbürette sowie einem programmierbaren Taschenrechner können Fällungstitrationen mit hoher Genauigkeit in einer der visuellen Titration vergleichbaren Zeit durchgeführt werden. Nicht zu verdünnte Lösungen (nicht unter 0,001 M) können im 95%-Vertrauensbereich auf ±0,01 ml und mit einer Genauigkeit von 0,1% analysiert werden.

     

Rapid determination of the equivalence volume in potentiometric acid-base titrations to a preset pH-I Theory and applications

A new approach to shorten the time needed for an acid-base titration has been made. The method developed is based on the equation for acid-base titrations derived by Ingman and Still. The equation is transformed into such a form that only one titration point is needed to calculate the equivalence volume when the titration is carried out to a preset pH which can be chosen according to the experimental conditions. The method is used for titration of acetic acid, log K(H)(HA) = 4.65, hydroxylammonium ion, log K(H)(HA) approximately 6.2, and boric acid, log K(H)(HA) approximately 9.1, with an error of 0.1-0.5%. In titration of hydrogen ascorbate ion, log K(H)(HA) approximately 11.3, the error obtained was about 0.3-2%.     

Evaluation of the equivalence point in potentiometric titrations with application to traces of chloride

A mathematical model applicable to the determination of the equivalence point (V_eq) is described. The regression equation is (1 + V/V₀)³E = Σ³_i= _0AiVⁱ, where E is the e.m.f. corresponding to volume V of titrant added, V₀ is the initial volume of titrand, and A_i are the regression coefficients. On the basis of A_i values obtained by the least-squares method, the algorithm for V_eq and the criterion of correctness of results obtained from measurements are presented. The method is applied to titrations of chloride with silver nitrate solutions.     

A modified gran method for determination of equivalence points in potentiometric precipitation titrations

Gran's method is frequently applied in potentiometric titration to obtain a more precise estimate of the equivalence point, particularly when the analyte concentration is too low to give well defined end-points. With precipitation reactions, however, when the analyte concentration is comparable to the solubility of the precipitate, even the use of Gran's method will not avoid significant errors. A correction term is introduced and a computer program outlined to overcome this problem. Titrations of 10^-4 M chloride are used for illustration.     

A source of error in the determination of equivalence volumes of carboxylic acids from potentiometric titrations

Emf measurements on mixtures of carboxylic acids, HA, and the corresponding bases, A, containing a high and constant salt background, show that the equation E = E₀ + glnh + j_hh commonly used in the calculation of equivalence volumes is not strictly followed. Terms linear in [HA] and [A] should be added. The origin of these terms is discussed briefly and their influence on the accuracy of equivalence-volume determinations is evaluated.     

Graphic determination of equivalence volumes in potentiometric titrations of mixtures of weak acids-I Two monobasic acids

A titration method for analysis of binary mixtures of weak acids is given. The equivalence volumes of the individual acids can be determined graphically from only two titration points. However, use of more than two points gives a more accurate result. Mixtures of acetic acid with ascorbic acid, hydroxyacetic and monochloroacetic (Delta log K(H)(HA), = 0.5-1.9) are titrated with an error of approximately, 0.5-2.5% in all three cases.     

Natural monocrystalline pyrite as electrode material for potentiometric titrations in water

The possibility of applying natural monocrystalline pyrite as sensor for the potentiometric titration of acids in water was investigated. The potential of this electrode in aqueous solutions exhibits a sub-Nernst dependence. In fresh solutions the slope (mV/pH) is 33.9. The potential jumps at the titration end-point obtained in titrations of HCl, H(3)PO(4) and CH(3) COOH do not differ much from those obtained by the application of the glass electrode as the indicator one. The potentials in the course of the titration and at the titration end-point (TEP) are rapidly established. The results obtained in the determination of the investigated acids deviated for 0.16-0.34% with respect to those obtained by using the glass electrode as the indicator one.     

On the accuracy of acid-base determinations from potentiometric titrations using only a few points from the titration curve

There are several procedures which use only a few points on the titration curve for the calculation of equivalence volumes in acid-base titrations. The accuracy of such determinations will depend on the positions of the points on the titration curve. The effects of errors in the stability constants and in the pH measurements on the accuracy of the analysis have been considered, and the results are used to establish the conditions under which these errors are minimized.     

Thermometric and potentiometric titrations of modified glass surfaces

Glass surfaces modified with N-2-aminoethyl-3-aminopropyltrimethoxysilane have been titrated with copper(II) by constant rate thermometric titration and by manual potentiometric titration with Gran plot end-point location. The results indicate that the titrant reacts with the bound ligand in a two-step process, with the thermometric titration responding to the first step and the potentiometric titration responding to the combined steps.     

Critical evaluation of potentiometric redox titrations in enology

Measurements of the zero current potential of a platinum electrode immersed in solutions of tanins or in wines of various origins, were performed during the additions of a solution of Ti(III), or of a solution of dichlorophenolindophenol (DCPIP), in order to obtain a global indication for the resistance to oxidation of some wines. The steady state intensity-potential curves on a platinum electrode highlight the occurrence of mixed potentials between the oxidation of ethanol or catechin and the reduction of oxygen present at very low concentrations, as well as the irreversibility of the redox system Ti(IV)/Ti(III). The adsorption of various species on the platinum and the slowness of the oxidation reactions by DCPIP exclude use of potentiometric titration theory. The shape of the potential-reagent volume curves depends on the nature of the solution and on the rate of reagent introduction. Generally, due to the slowness of the oxidation reactions with DCPIP it is impossible to find a linear relationship between the volume of titrant solution necessary to reach the inflexion point of the curves and the solution composition.     

Determination of the equivalence point in potentiometric titrations with gran's first method used to test the electrode response

Gran's first method is compared to the standard addition (subtraction) method. It is shown that Gran's first method canbe used to test the electrode response of, for example, a copper-selective electrode.     

Rapid determination of the equivalence volume in potentiometric acid-base titrations to a preset pH-II Standardizing a solution of a strong base, graphic location of equivalence volume, determination of stability constants of acids and titration of a mixture of two weak acids

A newly proposed method of titrating weak acids with strong bases is applied to standardize a solution of a strong base, to graphic determination of equivalence volume of acetic acid with an error of 0.2%, to calculate the stability constants of hydroxylammonium ion, boric acid and hydrogen ascorbate ion and to analyse a mixture of acetic acid and ammonium ion with an error of 0.2-0.7%.     

Conductometric and potentiometric titrations of nitrogen bases in non-aqueous solvents

This paper describes an experimental study of the conductometric and potentiometric titrations of nitrogen bases in non-aqeous media. It is shown that for bivalent bases the factors governing the shape of the titration curve are the same as those previously found for dibasic acids, viz. solvent, acid anion, temperature, and distance between basic groups. With the aid of this knowledge a new indifferent solvent system for potentiometric titrations has been developed, which is very attractive for the analysis of mixtures of bases.     

On the use of the mercury electrode in chelatometric potentiometric titrations

Summary Information is given on the applicability of the mercury electrode in chelatometric potentiometric titrations. The influence of ternary complex formation, the formation of precipitates on the electrode and possible errors, due to the asymmetric shape of the titration curves are discussed.

---

Über die Verwendung der Quecksilberelektrode bei chelatometrisch-potentiometrischen Titrationen

Zusammenfassung Einige Betrachtungen werden angestellt über die Anwendung der Quecksilberelektrode für komplexometrische Titrationen mit potentiometrischer Endpunktsanzeige. Der Einfluß der Bildung ternärer Komplexe, die Bildung von Niederschlägen auf der Elektrode und die Fehler infolge der Asymmetrie der Titrationskurven werden besprochen.

     

Analysis of variance applied to determinations of equilibrium constants

The statistical analysis of variance has been applied to the values of the equilibrium constants of the glycinate-proton and glycinate-nickel systems, determined in different laboratories by pH-titration in aqueous solution. The analysis shows how the main part of the error derives from the variability from one titration to another even in the same laboratory. Therefore the data for a single titration (k) must be processed separately, thus yielding a mean value for the equilibrium constant logbeta (pqr)(k) of the species M(p)H(q)L(r); from these mean values for different titrations in each laboratory l, a within-laboratory grand average, logbeta (pqr)(l), can be calculated; the variance of this grand average measures the experimental error. A further analysis of the data from the different participating laboratories shows that there were no significant differences between laboratories for the constants reported. From these results it can be inferred that all the values of the mean constants logbeta (pqr)(k) for one species, as determined separately for each titration in four laboratories, belong to the same population. A chi(2) analysis of these populations demonstrates that the stability constants of the species HL, H(2)L(+), NiL(+), NiL(2) (with L(-) = glycinate) are normally distributed, but not that for NiL(-)(3). Therefore, general mean values of the first four constants can be calculated and proposed as reliable standard values at 25 degrees and I = 1.0M Na(Cl): protonation of glycinate, log beta(011) = 9.651(12), log beta(021) = 12.071(26); nickel-glycinate complexes, log beta(101) = 5.615(35), log beta(102) = 10.363(62). These values indicate that the standard deviations are rather higher than those often reported in the literature.     

Amperometric and constant-current potentiometric determinations of the Landolt effect

An amperometric method with one platinum indicator electrode as well as the constant-current potentiometric method with one and two indicator electrodes were successfully applied to the Landolt effect determination by means of the hydrogen peroxide-iodideascorbic acid and bromate-bromide-ascorbic acid indicator reactions. The possibilities of application of these methods are illustrated by the determination of small amounts of iron(III), vanadium(V), and molybdenum(VI) with satisfactory accuracy and precision.