Titration conductance

Directions are provided for the quantitative analyses of Ck and P04 , and for conducting titrations of strong acids and strong bases. 

Scheme 13.3 Di-iodine - thione interactions detected by conductivity titrations...

Change in conductance as Au scanning tunneling microscope tip immersed in dithiol solution is withdrawn from Au substrate. [From x. Xiao, B. Xu, and N. Tao, Conductance Titration of Single-Peptide Molecules. J. Am. Chem. 

The basicity of the acid has also been determined by conductivity titrations.1... 

If the strong acid is titrated with a weak base, e.g., an aqueous solution of ammonia, the fii st part of the conductance-titration curve, representing the neutralization of the acid and its replacement by a salt, will be very similar to the first part of Fig. 24, since both salts are strong electrolytes. When. the equivalence-point is passed, however, the conductance will remain almost constant since the free base is a weak electrolyte and consequently has d very small conductance compared with that of the acid or salt. 

One of the valuable features of the conductance method of analysis is that it permits the analysis of a mixture of a strong and a weak acid in one titration. The type of conductance-titration curve using a weak base is shown in Fig. 26 the initial decrease is due to the neutralization of the strong acid, and this is followed by an increase as the weak acid is replaced by its salt. When the neutralization is complete there is little further change of conductance due to the excess weak ba.se. The first point of intersection gives the amount of strong acid in the mixture and the difference between the first and second is equivalent to the amount of weak acid. 

Fio. 26. Conductance titration of mixture of strong and weak acid... 

A desoxyribonucleo-depolymerase is present in ox pancreas and calf thymus, and in extracts of the germs of Lima bean, sunflower, maize, wheat, and pumpkin. It is not the same as the crystalline ribonucleo-depolymerase, which is devoid of action on desoxyribosenucleic acid. Action of this depolymerase on desoxyribosenucleic acid causes an increase of acidity and conductivity titration of the extra acidity liberated indicates that the final product is a pentabasic tetranucleotide. Greenstein and Jenrette found that the depolymerase also destroys the structural or anomalous viscosity. 

Neutralization reactions can also be looked at through conductivity tests. If a conductivity titration is performed with diluted hydrochloric acid and diluted sodium hydroxide solution (see E7.14), one would attain a certain minimum of electrical conductivity at the equivalence point, but it is not zero (see left diagram of Fig. 7.15) Na + (aq) ions and CF(aq) ions are left behind in the solution and are responsible for the minimal conductivity. The decrease in conductivity is often explained by the misconception that the absolute number of ions decreases and that by the usual ionic equation from an initial number of four ions, only two remain ... 

Fig. 7.15 Diagrams of conductivity titrations of hydrochloric acid and acetic acid [15]...

The conductivity can go down to zero if an insoluble salt is produced by the neutralization reaction. If one carries out a conductivity titration of barium hydroxide solution with diluted sulfuric acid, it is possible to observe a decrease in electrical conductivity (see E7.15). However, because additional white barium sulfate is precipitating, conductivity goes down to almost zero Ba2 + ions and S042 ions do not remain mobile, but form the ion lattice of barium sulfate crystals. 

E7.15 Conductivity Titration of Baryta Water with Sulfuric Acid Solution... 

The apparatus required for making conductance measurements and performing conductance titrations is generally inexpensive and basically simple in detail. For these reasons, the measurement of conductance finds wide acceptance in industry as an analytical tool, both in the laboratory and in process control. 

Many applications of conductance titrations involve acid-base titrations. 

In general, nonaqueous conductance titration is superior to other electrochemical methods for analyzing difficult systems. The major difficulty is the developmental work needed to establish suitable endpoints for the particular solvents and titrants required. 

Titration Curves. Generally it can be expected that if a low-frequency conductance titration can be performed, a high-frequency one can also. However, the cell size, ionic strength of the solution, and frequency needed to give a good endpoint are variables that must be determined by trial and error. Even after the best conditions are found, the curves obtained may be nonlinear and show little response. However, if an endpoint can be found, there is a definite advantage to a method in which no... 

Jasinski and Pawlak showed that the analysis of conductance titration curves developed by Kolthoff and Chantooni for acetonitrile solutions holds also for nitromethane. 

All the classical experimental methods have been brought to bear on acid-base reactions in these solvents. There is space to cite only a few. The conductance studies of Shedlovsky and his collabora-tors 20i.F204.F206.F207 hydrochlorfc and acetic acids in ethanol and 1-propanol are models of careful work. Less precise but still useful results have been obtained from conductance titrations in such solvents as f-butyl alcohol. ° ... 

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