Conductometric titrations applications

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. 

The aforementioned application of conductometry in Lewis titrations was an incentive, in addition to our potentiometric studies, to investigate also conductometric titration in non-aqueous media more thoroughly. Figs. 4.10 and 4.11 show two selected examples of the study. 

Conductometric titrations. Van Meurs and Dahmen25-30,31 showed that these titrations are theoretically of great value in understanding the ionics in non-aqueous solutions (see pp. 250-251) in practice they are of limited application compared with the more selective potentiometric titrations, as a consequence of the low mobilities and the mutually less different equivalent conductivities of the ions in the media concerned. The latter statement is illustrated by Table 4.7108, giving the equivalent conductivities at infinite dilution at 25° C of the H ion and of the other ions (see also Table 2.2 for aqueous solutions). However, in practice conductometric titrations can still be useful, e.g., (i) when a Lewis acid-base titration does not foresee a well defined potential jump at an indicator electrode, or (ii) when precipitations on the indicator electrode hamper its potentiometric functioning. 

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. 

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... 

Potentlometrlc titration has also been widely applied to polyelectrol des and proteins conductometric titration to a lesser extent. For colloids with a variety of different groups (proteins), application of the Henderson-Hasselbalch equation (3.6.52 or 531 or Its semi-emplrlcal variant [3.6.54] Is viable only when the pK s of the various groups are sufficiently far apart. 

Conductance measurements are useful as aids in the solution of many physico-chemical problems. A few of the more important of these applications are (a) determination of the solubilities of certain substances, (b) estimation of the degree of hydrolysis of salts, (c) determination of speeds of reaction, (d) investigation of molecular complexes and (e) conductometric titrations. These will be considered in the order given. The discussions will be brief since the chief purpose of this chapter is to illustrate the use of conductance measurement as an analytical method in other than electrochemical fields of investigation. 

Advantages and Limitations of Radiometric Titrations. Radiometric detection of the equivalence point is a general method that does not depend on the chemical reaction employed. This contrasts with other methods of detection, which depend on specific chemical or physical transitions at the equivalence point. Amperometric titrations are applicable only to electrochemically active systems conductometric titrations apply only to ionic solutions, and so on. In principle, any titration system in which a phase separation can be effected is amenable to radiometric detection, provided there exist suitable radioactive labels. The major limitation of the method is the requirement for phase separation. In precipitation titrations, the phase separation is automatic and the method is well suited to this class of titrations. For other classes of titrations, special phase-separation methods, such as solvent extraction, need to be applied. At the present time, the method suffers from a lack of phase-separation techniques suitable for continuous monitoring of the titration curves. 

A discussion of the chemical drive of solvation and hydration processes, respectively, leads to the introduction of the basic concept of electrolytic dissociation, the disintegration of a substance in solution into mobile ions. Subsequently, we learn about the migration of these ions along an electric potential gradient as a special case of spreading of substances in space. The ionic mobilities provide a link to conductance and the related quantities conductivity as well as molar and ionic conductivity. For determining the conductivity of ions experimentally, the introduction of the term transport number which indicates the different contribution of ions to the electric current in electrolytes is very useful. In the last section, the technique for measuring conductivities is presented as well as its application in analytical chemistry where conductometric titration is a routine method. 

Nearly all chemical sensors useful for liquid samples can be utiUzed to indicate titrations. Besides the preferred potentiometric, other electrochemical probes are also used, mainly amperometric and conductometric sensors. The so-called biamperometric titration works with simple wire pairs. Photometric and thermometric indication techniques are less common than electrochemical methods. Miniaturization does not play an important role for titration probes. Classical arrangements predominate to this day. Commercial titration instruments are only slowly starting to make use of the achievements of modern sensor technology. As an example, optodes have achieved a certain popularity in recent years for titration applications. 

The first procedure is only applicable with confidence to fresh hops or hop extracts. The second procedure can be improved as explained above and further on, by simply changing the pH of the buffer. The third procedure is needlessly complex and furthermore suffers from a few basic drawbacks as discussed extensively earlier (10). A procedure which can be recommended and which in fact is based on the second one of Analytica-EBC, is presented below. It is very close to the procedure described in Analytica-EBC Fourth Edition, where further details on safety precautions, instrumentation for conductometric titration and standardization of the lead(ll) acetate solution can be found. fat For hop extracts. 

As with amperometric titrations, to have straight-line portions of the titration curve dilution corrections must be made because the response is directly dependent on the concentration of the ionic species. Also, the important data are taken before and after the equivalence point rather than precisely at the equivalence point. The general conditions for effective conductometric measurements of solutions are discussed in Chapter 5 and are directly applicable when the system is used as the endpoint detection method. A particularly complete review of the subject has been presented.8... 

This last group of solvents includes substances as diverse as acetone and benzene. Acid-base reactions in such solvents are complicated by extensive ion-pairing and by formation of other ionic and molecular aggregates. In acetone, which has a dielectric constant of 20.7 at 25°C, sodium perchlorate at O.OIM concentration is 80% associated to ion-pairs whereas the degree of association is only 31 % in nitromethane, 22% in acetonitrile, and 4% in sulpholane. In other respects acetone behaves like the dipolar aprotic solvents discussed in sect. 3.6. Jasiiiski and Pawlak, for example, showed that conductance titrations in acetone could be treated quantitatively in the same way as those in acetonitrile. The familiar potentiometric, conductometric, and spectrophotometric methods are applicable to the ionisation of anilines in acetone and acetone-water mixtures/ ... 

Conductometric titrimetry is widely applicable for titration reactions involving ions. Figure 14... 

Electrolytic cells and temperature-responsive devices, such as thernristors and bolometers, are common examples of transducers whose electrical resistance or conductance varies in response to an analytical signal. These devices are used for conductometric and thcr-momctric titrations, for infrared absorption and emission measurements, and for temperature control in a variety of analytical applications. 

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