Simple instrument for titrimetry without visual indicators. Gasometric titrations: Argentometry

Several argentometric determinations have been worked out to show that the gasometric titration method is applicable not only to acid-base and redox reactions, but also to precipitation and complex-formation reactions. The processes reported allow the direct and indirect determination of iodide and cyanide, as well as the direct titration of silver ion in soluble and slightly soluble silver salts.     

Simple instrument for titrimetry without visual indicators. gasometric titrations: Cerimetry,chlorometry, nitrate,nitrite, hydroxide and carbonate determination

It was shown in previous papers, that many titrimetric problems can be solved by observing the pressure change of a closed system above the solution titrated at the equivalence point. This principle was made the basis of a gasometric titration method in which the end-point is found graphically. The titrant is added to the sample solution in measured increments at fixed intervals of time and the corresponding gas pressure or volume of the system is recorded and then plotted against the volume of added titrant. Half a dozen readings are sufficient to establish the end-point of a titration, which is found at the intersection of two straight lines. This graphical method was applied to cerimetry and chlorometry, as well as to some other analytical reactions (determination of nitrite, nitrate, hydroxide and carbonate) already described in previous papers on the gas pressure end-point technique. The results are comparable in precision and accuracy to the values obtained by the conventional visual end-point titrations. A gasometric titration takes about 10 minutes. The presence of other substances in the sample capable of reacting with the titrant does not necessarily cause interference.     

Simple instrument for titrimetry without indicators gas pressure end-point technique: Acid-base reactions

Visual changes in the liquid titrated cannot always be used for the detection of the end-point in volumetric analysis. To help analysts who do not have at their disposal the more or less complicated and expensive instruments required to solve those cases, the present paper suggests a simple titrimetric technique. The direction of the pressure change (gas evolution or gas absorption) at the equivalence point, in a closed system above the solution titrated, is observed in an easily assembled glass apparatus. Results obtained with this technique in the solution of acidimetric and alkalimetric problems are reported. They are comparable in precision and accuracy to the values obtained by the usual indicator titrations. The appaiatus described is useful for the analysis of 0.01N or more concentrated solutions.     

Simple instrument for titrimetry without indicators gas pressure end-point technique: Iodometry,iodimetry, iodate and periodate titrimetry

The present paper shows, that the gas pressure end-point technique can be applied to several oxidation reduction titrations. lodometry, iodimetry, iodate and periodate titrimetry were studied. Standard arsenite, iodine and hydrazine sulfate solutions òwere used as titrants. The results are comparable in precision and accuracy to values obtained by the standard visual end-point titrations.     

Reversible indicators for use in potassium bromate titrations

A review has been given of reversible indicators for use in bromate titrations. An examination has been made of four reversible indicators, α-naphthoflavone, p-ethoxy-chrysoidine. fuchsin and apomorphine.' All four indicators are satisfactory, but α-naphtho-flavone gives the sharpest end-points. Fuchsin and p-cthoxychrysoidine are gradually destroyed when the end-point is passed and re-passed several times. Apomorphine is only suitable for the titration of trivalent antimony and the end-point is the least sharp of all four indicators.Only α-naphthoflavone is suitable for the titration of 8-hydroxyquinoline solutions. Although it is possible to titrate directly and even back-titrate with standard 8-hydroxyquinoline, the method is not suitable because of the slow reaction between bromine and 8-hydroxyquinoline. The titration can be carried out satisfactorily, however, by adding excess bromate, then excess arsenite and re-titrating with bromate. The other two indicators are not suitable for this purpose; in the direct titration they tend to be destroyed by prolonged contact wth the excess bromine which is always present and, in any case, their colours are obscured by that of the 8-hydroxyquinoline so that the back-titration method is unsatisfactory.Aluminium can be determined satisfactorily after precipitations as the 8-hydroxyquinolate by titration with bromate and arsenite using α-naphthoflavone as indicator.     

Extractive indicators in complex-formation titrations: theory and practice

The use of conditional constants to predict the optimum conditions for titration in several complex-formation titrations, in which the end-point is detected by the formation of a coloured extractable complex, is demonstrated. The predictions have been tested by experiment. 2-(2-Pyridylazo)-1-naphthol is shown to be a useful extractive indicator for the copper-EDTA titration; dimethylglyoxine is not recommended as an extractive indicator for the nickel-EDTA titration; the titration of fluoride with aluminium, using 8-hydroxy-quinoline as an extractive indicator, is shown to be undesirable theoretically and experimentally.     

Colour changes of chemical indicators-VI: metallochromic indicators for direct chelometric titrations of zinc

Eriochrome Blue SE, Eriochrome Red B, Naphthylazoxine 6S, SNAZOXS, and Zincon have been studied in order to find optimum conditions for their use as metallochromic indicators in direct visual chelometric titrations of zinc. The sharpness of the indicator transitions has been investigated by means of photometric titrations and the colour quality has been specified with the aid of the C.I.E. chromaticity systems. Zincon and Eriochrome Blue SE have been found to be the most convenient for visual titrations of zinc.     

Total systematic error in redox titrations with visual indicators--II. Experimental verification

The equations for calculating the transition potential of a redox indicator and the total titration error have been verified experimentally. Good agreement has been obtained for reversible indicators such as Variamine Blue, 4-methyl-4'-aminodiphenylamine and ferroin. In the latter case it was shown that at the usual concentrations the indicator acts as a one-colour indicator, whereas for higher concentrations its behaviour is typical of a two-colour indicator. In the case of a pseudoreversible indicator--diphenylaminosulphonic acid--the calculated values give only the minimum error. In real conditions the error is always more positive.     

Total systematic error in redox titrations with visual indicators--I: basic principles

The following factors contribute to the total error in redox titrations with visual indicators: the end-point error (DeltaV(T)), which arises from the difference between the potential of the equivalence point and that of the actual end-point determined by a given indicator ; the indicator consumption error (DeltaV(T)), which arises from the amount of indicator oxidized (or reduced) by the titrant; the irreversibility error, which is in fact a part of the indicator consumption error, arising from the generally uncontrolled processes connected with the irreversibility of the redox processes, decomposition of the reaction products, etc. The first two factors can be evaluated on the basis of the physicochemical characteristics of all the systems involved. They contribute to the total systematic error. The third, being not strictly controlled, in general increases the positive indicator consumption error, depending on such parameters as rate of titrant addition, stirring, effect of decomposition products on the potential, etc.     

Titrations with piezoelectric monitoring : Part 2. Compleximetric titrations and precipitation titrations

A piezoelectric detector is used to monitor titration reactions involving complex formation or precipitation. Analytes at concentrations down to 10^?4 mol 1^?1 can be determined. The frequency shift in the compleximetric titrations is affected by the composition of the solution, the buffer and competing ligands present in the solution. Factors influencing the frequency shift in the precipitation titration are also investigated.     

Hydrophobic indicators for two-phase titrations and their application to the determination of silver and pentachlorophenol

The hydrophobic dyes tetrabromophenolphthalein ethyl ester and 2,6-dichlorophenolindo-phenol are proposed as visual indicators for two-phase titrations. The aqueous phase is colourless throughout the titration and these indicators make it possible to detect the end-point of the titration by the colour of one or the other phase. The indicators allow the two-phase titration of the silver(I)-1,10-phenanthroline complex with tetraphenylborate and of pentachlorophenol with tetraphenylphosphonium chloride.     

Studies on metallochromic indicators--II. Zincon and its mercury and zinc complexes as indicators in EDTA titrations

Zincon has been found to be an excellent indicator in the titration of mercury(II) with EDTA at pH 5.5-7. Moreover the mercury(II)-Zincon and zinc-Zincon systems have been found to be suitable indicators in the direct EDTA titrations of Pb(2+), Cd(1+) and Ca(2+). Interference studies of a number of cations and anions have been made. Chloride and bromide can be tolerated in the titration of mercury(II), up to equivalent concentrations.     

Potentiometric titrations with ion-exchanging membrane electrodes: Part II. Theoretical aspects of simple precipitation titrations

Titration curves were derived for potentiometric titrations with zero electric current, utilizing a membrane electrode as indicating electrode, the membrane consisting of permselective, ion-exchanging material. As a first example, calculations were made for simple precipitation titrations with only +1 or -1 charged ions present in the solution to be titrated and in the reagent. For the calculations of the membrane potentials the theory of TEORELL and MEYER and SIEVERS was used. The influence of several parameters, such as the diffusion coefficients of the ions, the capacity of the membrane and the concentration of the solutions, was examined.     

Single-point titrations: Part-I. The determination of bases

Equations are derived for the calculation of acid mixtures, which upon titration with base show a linear relation between pH and the amount of base. Three to five weak acids were used and a linearity of better than ±0.02 pH units was obtained. The use of such mixtures for analysis of the base content of samples by means of a single pH measurement is described. A procedure for obtaining conditional pK_a values of the components of the acid mixture is also described. The single-point titration method is advocated for use when better accuracy than that of direct potentiometry is desired but less than that of an ordinary titration can be accepted. It is not necessary to know the pK_b or the number of weak bases.     

Single-point titrations: Part II. Experimental determination of bases

An acid—base mixture is described which has linear pH response when titrated with strong base. The concentrations of the separate components in the mixture are given. Determinations of bases in the tange 0.05 M—0.25 M with a relative standard deviation of less than 0.5 % are reported. The method of preparing the mixture as well as some interferences of high salt concentrations in the sample are discussed.     

Computer-controlled titrations: Part 1. Considerations based on systems theory

Automated titrimetric procedures are considered on the basis of systems theory, with emphasis on the dynamic behaviour of the system. In the case of continuous addition of titrant, conditions are derived for the maximum addition speed and a correction procedure is given. Control algorithms for discontinuous addition of titrant are given, including an algorithm for on-line estimation of the dynamic (overall) effects of the titration system; this is useful for determining the waiting time between two successive additions of titrant. Shannon's theorem is utilized in order to decide on the sampling of the titration curve, both for continuous and discontinuous additions of titrant. Finally, confidence intervals for the end-point determination are derived, based on zero crossing statistics, and applied on the second derivative of a sigmoidal titration curve.     

Potentiometric titrations in non-aqueous solution : Directions for choosing solvent-titrant combinations

This paper contains tables and a number of simplified considerations, which will enable the analytical chemist not specialized in the subject to find suitable media for titration in non-aqueous solution of most of the acids and bases commonly encountered in analytical practice, Tables providing guidance in the titration of mixtures of not too closely similar acids or bases are also given Examples illustrating the application of these tables are included.     

Behaviour of series piezoelectric sensor in electrolyte solution : Part II. Applications in titrimetry

The applications of a series piezoelectric sensor for end-point determination in frequencimetric titrations, including neutralization, precipitation, complexation and redox titrations, are reported. The method is based on the fact that a series piezoelectric sensor shows a sensitive and selective frequency response to changes in conductivity of solution and can be applied to sample solutions containing large amounts of unreacted foreign electrolytes.     

Studies on adsorption indicators : Titration of iodide in presence of chloride. mechanism of the colour changes during argentometric titrations with congo red as adsorption indicator

Congo red is a suitable indicator for the titration of iodide in presence of chloride with silver solution at pH 5–5.5. The behaviour of congo red as an adsorption indicator is described in detail. The silver compound of congo red has been isolated and its properties investigated.