Indicators acid-base, characteristics

Crystallochemical examination of acid-base characteristics of the borates indicates ways to search for new compounds with desirable composition, structure and properties and facilitates evaluation of preferable flux systems for their crystallization. 

Methylene blue binding does not predict the Lewis acid-base characteristics of the pulp but might be useful as an indicator of other properties in a product derived from the pulp. It does indicate that some change was made in the binding properties of the pulp. 

Gutmann proposed that acid-base characteristics could be represented by a donor number, generally designated as DN (a single symbol, not a product) and an acceptor number AN. DN represents the base properties of the molecule and is essentially a molar heat of reaction with a reference acid, under standardized conditions. AN represents the acid properties of the molecule. The asterisk in AN indicates that the original Gutmann values have been corrected for dispersion force interactions and are expressed as molar enthalpies. Jensen has discussed limitations of the Gutmann DN/AN theory. ... 

A simple, reliable, and fast method of determining the pH of a solution and of monitoring a titration is with a pH meter, which uses a special electrode to measure H 0+ concentration. An automatic titrator monitors the pH of the analyte solution continuously. It detects the stoichiometric point by responding to the characteristic rapid change in pH (Fig. 11.9). Another common technique is to use an indicator to detect the stoichiometric point. An acid-base indicator is a water-soluble organic dye with a color that depends on the pH. The sudden change in pH... 

An acid—base indicator changes color with pH because it is a weak acid that has one color in its acid form (HIn, where In stands for indicator) and another color in its conjugate base form (In-). The color change results because the proton in HIn changes the structure of the molecule in such a way that the light absorption characteristics of HIn are different from those of In. When the concentration of HIn is much greater than that of In, the solution has the color of the acid form of the indicator. When the concentration of In is much greater than that of HIn, the solution has the color of the base form of the indicator. 

The absorption characteristics of solutions of the acid-base indicator methyl red at two wavelengths... 

Observations that the presence of protein affects the colour change of some indicators used in acid-base titrations led to the development of methods for the quantitation of proteins based on these altered absorption characteristics of such dyes. As the presence of protein alters the colour produced by these indicators when measuring pH, so in the quantitation of proteins using dye-binding methods the control of pH is vital. 

The last of these methods has been applied particularly to chemical reaction vessels. It is covered in detail in Chapter 17. In most cases, however, the RTDs have not been correlated with impeller characteristics or other mixing parameters. Largely this also is true of most mixing investigations, but Figure 10.3 is an uncommon example of correlation of blend time in terms of Reynolds number for the popular pitched blade turbine impeller. As expected, the blend time levels off beyond a certain mixing intensity, in this case beyond Reynolds numbers of 30,000 or so. The acid-base indicator technique was used. Other details of the test work and the scatter of the data are not revealed in the published information. Another practical solution of the problem is typified by Table 10.1 which relates blend time to power input to... 

Reactions with indicators. Acids and bases provide characteristic reactions with indicators that change colors during neutralization. 

Certain of the following test solutions are intended for use as acid-base indicators in volumetric analyses. Such solutions should be adjusted so that when 0.15 mL of the indicator solution is added to 25 mL of carbon dioxide-free water, 0.25 mL of 0.02 N acid or alkali, respectively, will produce the characteristic color change. 

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