Conductometric analysis titration

Vol 2 (1951), 51-104 (Conductometry) 3)J.J. Lingane, "Electroanalytical Chemistry , Interscience, NY (1958), Chap EX (Conductometric Analysis) 4)A.Weissberger, Edit, Physical Methods of Organic Chemistry , VolL, Pt 4, Interscience, NY (I960), Chap 45 (Conductometry) 5)Vogel (1961), 969-87 (Conductometric titrations)... 

Conductometric analysis using a 2-propanol/toluene/water solvent mixture in the titration of fresh and used oil samples (Armitage et al., 1987, Pawlak, 1980) and benzene/alcohol solvent mixture for the titration of phenolates and sulfonates (Labre and Briant, 1960) have been found to give satisfactory results however, benzene is a class A carcinogen and is no longer used in most laboratories. 

Table 15.4 shows some typical limiting ionic equivalent conductivities. From this we can deduce that the limiting equivalent conductivity of potassium nitrate is (K ) + (NOJ) = 74 + 71 = 145, and that of nitric acid is (H" ") + (NOJ) = 350 + 71 =421, assuming 100% dissociation into ions. The change in conductivity of a solution upon dilution or replacement of one ion by another by titration is the basis of conductometric analysis. 

A modified method for Wollmer analysis of hop extracts is given by the EBC [25]. This method gives values for total resins and soft resins (and hard resins by difference). The a-acid content can be determined by conductometric lead titration of the soft resin which, when deducted from the soft resin figure, gives a value for the -fraction. 

Conductometric analysis of some latexes leads to the conclusion that most of the polymerized acid ends up on the surface of the particles while in other systems a majority of the acid is not titratable and is assumed to be buried within the particles. For instance, conductometric titrations of the three latexes described in Figure 12 showed that greater than 90% of the acrylic acid added in the polymerization was associated with the particles and titratable. On the other hand, polystyrene and poly(methyl methacrylate) latexes generally yielded conductometric results showing a considerable fraction of the acid buried (31). Since, at the levels of incorporated acid studied, the PST and PMMA latexes did not expand upon raising the pH, it could be argued that in the acrylic case (Fig. 12) all the acid was detected because the particles expanded to bare previously buried groups. But poly(butyl acrylate) latexes were found to exhibit no expansion when neutralized with base, and conductometric titrations showed that most of the acid added in the polymerization was detected on the particles (39). 

Conductometric titration of alpha acids was in the not so distant past the most common procedure in the brewery laboratories. In this method, a suitable solution of an extracted hop or of the dissolved hop extract is titrated with a solution of lead(ll) acetate and the conductivity plot allows deduction of the results. Many contributions on the conductometry of alpha acids have appeared in the literature. The titration curve can be influenced substantially by changing the titration medium, as we found out for a number of mixed solvents (10), Current methods add either a base or dimethylsulfoxide to improve the determination of the titration endpoint. The Analysis Committee of the European Brewery Convention repeatedly organized collaborative trials to evaluate hop conductometric analysis. The efforts of a Working Group on Hop... 

Three conductometric analysis techniques are mentioned in Analytica-EBC Fourth Edition (1987). The first is a very simple procedure. The hop or hop extract is extracted-dissolved in toluene and the alpha acids are titrated in the same toluene solution. The second is a Verzele procedure which uses a two phase system consisting of toluene and a buffer pH 7, to extract the hops or to dissolve the hop extract. Titration follows in toluene with DMSO added. The third method or Ganziin procedure uses a complex mixture of methanol, diethylether and hydrogen chloride to obtain a suitable solution of the alpha acids. Titration follows in ethanol DMSO solution. 

End Point Determination Adding a mediator solves the problem of maintaining 100% current efficiency, but does not solve the problem of determining when the analyte s electrolysis is complete. Using the same example, once all the Fe + has been oxidized current continues to flow as a result of the oxidation of Ce + and, eventually, the oxidation of 1T20. What is needed is a means of indicating when the oxidation of Fe + is complete. In this respect it is convenient to treat a controlled-current coulometric analysis as if electrolysis of the analyte occurs only as a result of its reaction with the mediator. A reaction between an analyte and a mediator, such as that shown in reaction 11.31, is identical to that encountered in a redox titration. Thus, the same end points that are used in redox titrimetry (see Chapter 9), such as visual indicators, and potentiometric and conductometric measurements, may be used to signal the end point of a controlled-current coulometric analysis. For example, ferroin may be used to provide a visual end point for the Ce -mediated coulometric analysis for Fe +. 

The first comprehensive investigation of the TaF5 - HF - H2O system was performed by Buslaev and Nikolaev [292]. Based on the analysis of solubility isotherms, and on conductometric and potentiometric titrations, the authors concluded that in this solution, tantalum forms oxyfluorotantalic acid, H2TaOF5, similar to the formation of H NbOFs in solutions containing NbF5. 

The quantitative analysis procedure involves gravimetric detn of the HMX on a moisture-free basis after benzene extraction of, and differential detn of TNT. Moisture content is detd by conductometric titration of sample in an acetic-sulfuric acid suspension. Acetone insoluble matter is determined gravimetrically... 

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. 

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. 

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) . 

Conductometric titration of ZrCl4 with KOPh in nitrobenzene indicates the formation of Zr(OPh)4, ZrCl3(OPh) and ZrCl2(OPh)2, which have been isolated and characterized by chemical analysis. The Lewis acidity of Zr(OPh)4 and ZrCl2(OPh)2 has been demonstrated by isolation of adducts with py, bipy, phen and their N-oxides.216... 

Electrochemistry finds wide application. In addition to industrial electrolytic processes, electroplating, and the manufacture and use of batteries already mentioned, the principles of electrochemistry are used in chemical analysis, e.g.. polarography, and electrometric or conductometric titrations in chemical synthesis, e.g., dyestuffs, fertilizers, plastics, insecticides in biolugy and medicine, e g., electrophoretic separation of proteins, membrane potentials in metallurgy, e.g.. corrosion prevention, eleclrorefining and in electricity, e.g., electrolytic rectifiers, electrolytic capacitors. 

For serum replacement (6), the latex is confined in a cell with a uniform-pore-size Nuclepore filtration membrane. Distilled, deionized water is pumped through the latex until the conductance of the effluent stream is about the same as that of the distilled, deionized water. This serum replacement removes the adsorbed emulsifier and solute electrolyte quantitatively and allows recovery of the serum in a form suitable for further analysis however, it does not+replace the Na+ and K counterions of the surface groups with Vl ions. To do this, dilute hydrochloric acid (ca. 10 N) is pumped through the latex, followed by distilled, deionized water to remove the excess acid. The latex is then titrated conductometrically to determine the surface charge. 

A polyvinyl acetate latex prepared by semi-continuous polymerization at 55° using a polymethacrylic acid-nonylphenol-poly-ethoxylate phosphate ester emulsifier and sodium persulfate-sodium formaldehyde sulfoxylate initiator (23). The latex was cleaned by ion exchange and serum replacement using both Nuclepore and Pellicon membranes, and the cleaned latex and serum fractions were analyzed by conductometric titration. In addition, the dried films were extracted with water and organic solvents, and the extracts were analyzed by infrared spectroscopy and thermo-gravimetric analysis. 

V Surface Characterisation, A quantitative analysis of the amounts of PAA associated with the latices was obtained by conductometric titration and a qualitative analysis of its behaviour by potentiometric titration. Titrations were performed under a nitrogen atmosphere using a Radiometer Autoburette system and a M64 pH meter together with a Wayne Kerr B642 Bridge. 

Table III Analysis of some conductometric titration data for the latices...

In order to compare the PMMA results with those obtained with the carboxylic acrylic latex, the concentration of surface carboxyls must be determined. Acid location analysis (5 was carried out for this purpose. Briefly, the latexes were titrated conductometrically with 0.1N NaOH followed by a titration of the aqueous phase from which the particles had been removed by centrifugation. The difference in the two titrations provided the distribution between surface and soluble acid. The deficit between the total acid thus determined and the concentration of acrylic acid used in the polymerization was termed "buried". Although some drift occurred in the conductance with time, an equilibration time of approximately 10 minutes per addition of sodium hydroxide was generally sufficient to yield stable readings. 

Analysis of the imine polymer can be performed by a colorimetric method which is based on the complexation reaction with copper [2], Elemental analysis serves for the determination of the nitrogen content. Potentiometric and conductometric titration is also used in analysis [3]. For quantitative routine determination, preferably in the form of the hydrochloride, refractometry is recommended. 

Conductivity, Electrical Conductometry and Conductometric Titrations. Electrical conductivity is thequality or ability of a substance to transmit electrical energy. If it deals with the conductivity of an electrolyte in solution, it is then called electrolytic conductivity. Conductometry deals with analyses by measuring electrolytic conductivity, based on the fact that ionic substances in many solvents conduct electricity. Conductometric titrations are quantative analysis based on the fact that with the addn of the titrating agent to a soln being titrated, the specific conductivity (reciprocal of specific resistance in mhos) changes at a different rate before and after the end point (Comp with Potentiometric Analysis) Refs 1 )Kirk Othmer 4 (L 949), 325-33 (Conductometry) 2)W.G.Berl, Edit, "Physical Methods... 

Important evidence of the ionic structure of many silane-uncharged nucleophile complexes in solution is their high electrical conductance, characteristic of strong electrolytes (239,252,254-256,263). The 1 1 stoichiometry of certain complexes in solution was proved by conductometric titration (Fig. 1). The stoichiometry in solids was, in many cases, confirmed by elemental analysis (239,260). 

The most convenient method of obtaining a direct measure of the sulfonate content of lignin in pulp has proven to be conductometric titration (Katz et al. 1984). The preferred method for analysis of total sulfur in lignin in pulp is combustion followed by ion chromatography (Douek and Ing 1989). 

Provided the described experimental procedure is followed, there seems to be little restriction in the use of the analysis. Typical data obtained by conductometric titration for the sulfonate contents of a variety of pulps and lignin are shown in Table 7.7.1 along with data obtained by other methods. 

Kojima Y, Hayashi A, Tachi I (1960) Studies on lignosulphonic acid (VI) Conductometric titration with weak base 7pn Tappi 14 831-834 Kolthoff IM, Sandell EB (1952) Textbook of quantitative inorganic analysis Macmillan, New York, 759pp... 

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