Titration conductometric method

The two variables change their role with respect to their dependent versus independent, intensive versus extensive nature. This is also true of e.g. calorimetric, conductometric and spectrophotometric titrations using UV-, IR- or NMR-spectrosco-py We additionally have to consider that in the titration of the catalytic process only the external dynamics are measured a direct comparison with the actual metal fraction of the related intermediate complexes is generally not possible We call this analysis of homogeneous catalytic systems by a metal-ligand titration the method of inverse titration and for the resulting diagrams we use the term li nd-concentration control maps ([L]-control maps) . 

Polystyrene latexes have been prepared using persulfate initiator for many years, but only recently have methods been developed to determine the number and loci of the sulfate surface groups. To determine these surface groups, the latex is cleaned to remove the adsorbed emulsifier and solute electrolyte, then the surface sulfate groups in the H+ form are titrated conductometrically with base. The latexes can be cleaned effectively by ion exchange (2-5) or serum replacement (6) dialysis is not effective in removing the adsorbed emulsifier and solute electrolyte (3,5,6). +... 

The conductometric titration method has several advantages over the potentiometric titration method. It is applicable in a straight forward manner, without back titration or other modifications, to the determination of TBN for a wide range of petroleum products including fresh and heavily used oils. The conductometric method is quick and easy to perform, with two intersecting lines at the equivalent point, also contamination of electrodes is eliminated. The... 

The TBN values obtained for the fresh, unused, lubricating oil additive package components show results from conductometric and IP 177 (potentiometric) methods being 90% to 98 % and 85% to 90%, respectively, of the corresponding IP 276 (potentiometric) values. The TBN values for some selective products such as zinc dialkyl-dithiophosphate (ZDDP) was observed as an inflection point using the IP 276 (potentiometric) back titration method and also the conductometric method. 

The electromotoric force (emf) of a cell depends on the ionic concentration of the solutions. To locate the equivalence point, the variation in emf is monitored as the concentration of the analyte changes. When the measured emf is plotted against the total volume of titrant added, the curve produced is similar to that of a titration curve Fig. 4. This technique has all the advantages of the conductometric method and gives an experimental curve from which the endpoint can be detected accurately. 

If the titrant is a weak electrolyte (such as ammonia), the curve is essentially horizontal past the equivalence point, which causes less uncertainty to the extrapolation of a curve. In titration of a weak base, such as acetate ion, with a strong acid, a salt and undissociated acetic acid are formed. After the endpoint is passed, a sharp rise in conductance attends the addition of excess hydronium ions. Salts whose acidic or basic character is too weak to give satisfactory endpoints with indicator are conveniently titrated with the conductometric method. The conductometric titration of a mixture of two acids that differ in degree of dissociation is frequently more accurate than a potentiometric titration. 

As mentioned previously, the conductometric method has few apphcations in food analysis. During the last year, CA Selects, Analytical Electrochemistry section, hsted only three papers on conductometric titrations, one of them on a PC-controUed automatic operation. In most cases, the apphcation involves the titration of acids or bases, although some apphcation applies to the determination of the halides, sulphides and mercaptans. 

Conductometric methods are useful in the titration of mixtures of strong and weak acids. Thus an analysis of a mixture of acetic and hydrochloric acids can be carried out with fair accuracy. The result of such a titration is shown in Fig. 7, also due to Kolthoff. The added base first reacts with the strong acid producing a break in the curve at the equivalence point, followed by another break in the curve when the weak acid is neutralized. As shown, the first intersection is far from being sharp. This is due to the commencement of the ionization of the acetic acid before all the hydrochloric acid has disappeared. However, the equivalence point can be established by extending the straight portions of the lines as indicated. 

The conductometric method of titration is of particular service when the reaction is the replacement of the anion of the salt of a weak acid with the anion of a strong acid. Thus, for example, in the titration of sodium acetate with hydrochloric acid the weak acid is liberated and... 

Oxidation-reduction titration using the conductometric method has been studied by Edgar12 and others. One example, the oxidation of ferrous iron by a dichromate, may be represented as follows ... 

The conductometric method may also be used in many titrations involving precipitations. For instance Harned13 has followed the conductance during the titrations of magnesium, nickel and cobalt sulphates with barium hydroxide. The resulting plots of the conductance against volumes of titrating fluid are all of the form shown in Fig. 9, two... 

We must also keep in mind that equivalence points of EDTA titrations can be detected by using several instrumental methods. A first method, potentiometry, was just mentioned. There are also other potentiometric methods, based on other principles than the previous one, that may be used. Amperometric and conductometric methods have been proposed equally (see electrochemical methods of analysis). Finally, we ll mention photometric and spectrophotometric indications. 

Finally, the sulfonate content of lignin is deterrnined by two main methods one typified by conductometric titration in which sulfonate groups are measured direcdy, and the other which measures the sulfur content and assumes that all of the sulfur is present as sulfonate groups. The method of choice for determining the sulfonate content of lignin samples that contain inorganic or nonsulfonate sulfur, however, is conductometric titration (45). 

Many experimental approaches have been appHed to the deterrnination of stabihty constants. Techniques include pH titrations, ion exchange, spectrophotometry, measurement of redox potentials, polarimetry, conductometric titrations, solubiUty deterrninations, and biological assay. Details of these methods can be found in the Hterature (9,10). 

Coulometry can be regarded as an analog of titration where the substance being examined is quantitatively converted to a reaction product not by the addition of titrant, but by a certain amount of electric charge Q. As in titration, the endpoint must be determined. To determine the endpoint during current flow, one combines coulometry with another of the electrochemical methods described, and accordingly is concerned with conductometric, potentiometric, or amperometric coulometry. 

Attention is finally focused on the advantages of conductometric titrations, which include (i) colored solutions where no indicator is found to function satisfactorily can be successfully titrated by this method (ii) the method is useful for titrating weak acids against weak bases, which does not produce a sharp change in color with indications in ordinary volumetric analysis and (iii) more accurate results are obtained because of the graphical determination of the end-point. 

Conductometric titrations offer several advantages compared with potentiometric titration methods, such as better precision and better differentiation of the basic components in polymers, but they are more laborious. ASTM D 4928-96 is an established KF method for the determination of water in crude oils. 

This method is primarily based on measurement of the electrical conductance of a solution from which, by previous calibration, the analyte concentration can be derived. The technique can be used if desired to follow a chemical reaction, e.g., for kinetic analysis or a reaction going to completion (e.g., a titration), as in the latter instance, which is a conductometric titration, the stoichiometry of the reaction forms the basis of the analysis and the conductometry, as a mere sensor, does not need calibration but is only required to be sufficiently selective. 

In fact, any type of titration can be carried out potentiometrically provided that an indicator electrode is applied whose potential changes markedly at the equivalence point. As the potential is a selective property of both reactants (titrand and titrant), notwithstanding an appreciable influence by the titration medium [aqueous or non-aqueous, with or without an ISA (ionic strength adjuster) or pH buffer, etc.] on that property, potentiometric titration is far more important than conductometric titration. Moreover, the potentiometric method has greater applicability because it is used not only for acid-base, precipitation, complex-formation and displacement titrations, but also for redox titrations. 

In general these methods are restricted to titrations, either conductometric or potentiometric. 

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