Acid-base indicators function

Calmagite. This indicator, l-(l-hydroxyl-4-methyl-2-phenylazo)-2-naphthol-4-sulphonic acid, has the same colour change as solochrome black, but the colour change is somewhat clearer and sharper. An important advantage is that aqueous solutions of the indicator are stable almost indefinitely. It may be substituted for solochrome black without change in the experimental procedures for the titration of calcium plus magnesium (see Sections 10.54 and 10.62). Calmagite functions as an acid-base indicator ... 

The electrochemical oxidation of aromatic aldehydes (1) must be studied in strongly alkaline media. Acidity functions for strongly alkaline aqueous solutions of alkali metal and quaternary ammonium hydroxides, corresponding to dissociation of proton (H ), are well established (2, 3). Substituted anilines and diphenylamines (4,5) and indoles (6) were used as acid-base indicators for establishment of such scales, but whether an acidity scale based on one type of indicator can be rigorously applied to acid-base equilibria involving structurally different acidic groups for reactions in strongly alkaline media remains questionable. For substituted anilines, behavior both parallel (7) and nonparallel (8) to the H scale based on indole derivatives has been reported. The limited solubility of anilines in aqueous solutions of alkali metal hydroxides, the reactions of the aniline derivative with more than one hydroxide ion, irreversible substitution reactions (9), and the possibility of hydroxide ion addition rather than... 

Substituted benzaldehydes have proved useful as acid-base indicators for reactions involving the addition of hydroxide ions n strongly alkaline aqueous media (19). It seemed logical to extend their use to solutions of sodium hydroxide in water-ethanol and water-DMSO mixtures. In ethanol-water, it was of interest whether the competition between addition of hydroxide and ethoxide ions will be reflected in the dependence of the J- function on ethanol concentration. In water-DMSO mixtures, it was important to investigate whether the radical change at higher DMSO concentrations, observed for H values and attributed to changes in solvation of the hydroxide ion, will be observed for the addition reaction as well. 

In a typical acid-base titration (Section 3.10), a solution containing a known concentration of base (or acid) is added slowly from a buret to a second solution containing an unknown concentration of acid (or base). The progress of the titration is monitored, either by using a pH meter (Figure 16.6a) or by observing the color of a suitable acid-base indicator. With a pH meter, you can record data to produce a pH titration curve, a plot of the pH of the solution as a function of the volume of added titrant (Figure 16.6b). 

Cytolysis wasn t the only method used to determine intracellular pH. In another approach, acid-base indicators such as methyl orange were diffused into living cell suspensions, and intracellular color changes corresponding to low pH were observed94,96. All the indicators used also function as irreversible redox indicators, however. Therefore, it is most likely that these indicators measured cell potential, not pH. 

Strongly functional cation and anion e.xchange resins when hydrated (swollen) dis.s K iute (ionize) giving an internal electrolyte which is undetectable externally unless ion exchange occurs. This fundamental property of ion exchange resins is easily demonstrated using coloured acid-base indicators. 

The blue dye lacca, which can be extracted from the lichens Roccella and Leca-nora with alkali and milk of lime, is the basis for the well-known litmus solution, which functions as an acid-base indicator in the pH range 4.4-8.0. The name litmus comes from the Dutch lackmoes (from moes = mush, paste). 

Explain what acid-base indicators are and how they function... 

Those substances, the color of which changes with the hydrogen ion concentration of a solution, have been called, until recently, Color Indicators. Unfortunately, this name is not exact, nor was it logically chosen, since oxidation-reduction, adsorption indicators, etc. are also accompanied by a color change when they function as indicators. Accordingly it is better to designate those substances, the color of which depends upon the acidity or alkalinity of a solution, as Acid-Base Indicators. In this monograph, they will be referred to simply as Indicators. 

Nitrobenzene functions as an acid-base indicator both in sulphuric acid and in hydrofluoric acid. 

Diagnostic aid for renal function determination. Used as a 0.1 % soln. in EtOH as an acid-base indicator (pH range 6.4-8.2 colour change yellow red). Bright-red cryst. Insol. CHCI3, Et20 sol. EtOH, dil. alkalis si. sol. H2O. p, 7.92 (20°). 557 nm. 

The initial goal of the kinetic analysis is to express k as a function of [H ], pH-independent rate constants, and appropriate acid-base dissociation constants. Then numerical estimates of these constants are obtained. The theoretical pH-rate profile can now be calculated and compared with the experimental curve. A quantitative agreement indicates that the proposed rate equation is consistent with experiment. It is advisable to use other information (such as independently measured dissociation constants) to support the kinetic analysis. 

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. 

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