Indicators transition range

Indicator Transition range (pH) Acid color Base color Preparation... 

For ferroin, with E° = 1.147 V (Table 16-2), we expect the color change to occur in the approximate range 1.088 V to 1.206 V with respect to the standard hydrogen electrode. With a saturated calomel reference electrode, the indicator transition range will be... 

The indicator transition range should overlap the steep part of the titration curve. 

Figure 16-3 Titration curves and indicator transition ranges for the analysis of mixtures containing hydroxide, carbonate, and hydrogen carbonate ions.

Used as redox indicator (transition range 1.08-1.12 V). Blue cryst. powder. Sol. H2O, EtOH, Me2CO insol. CCI4. E° + 1.10 V. 

A selected list of redox indicators will be found in Table 8.26. A redox indicator should be selected so that its if" is approximately equal to the electrode potential at the equivalent point, or so that the color change will occur at an appropriate part of the titration curve. If n is the number of electrons involved in the transition from the reduced to the oxidized form of the indicator, the range in which the color change occurs is approximately given by if" 0.06/n volt (V) for a two-color indicator whose forms are equally intensely colored. Since hydrogen ions are involved in the redox equilibria of many indicators, it must be recognized that the color change interval of such an indicator will vary with pH. 

Dilute solutions of nominally 0.001 M NaOH and HGl are used to demonstrate the effect of an indicator s color transition range on titration error. Potentiometric titration curves are measured, and the indicator s color transition range is noted. Titration errors are calculated using the volume of titrant needed to effect the first color change and for a complete color change. 

In this experiment the effect of a mixed aqueous-organic solvent on the color transition range of common indicators is investigated. One goal of the experiment is to design an appropriate titrimetric method for analyzing sparingly soluble acids and bases. 

The examples of ArF (193 nm), KrF (248 nm), XeF (351 nm), KrCl (222 nm), XeCl (308 nm) and XeBr (282 nm) indicate the range of wavelengths from excimer lasers. Because the ground states of these molecules are not totally repulsive but very weakly bound, there is a very shallow minimum in the potential curve, as illustrated in Figure 9.15. In the case of XeF the potential energy minimum is relatively deep, about 1150 cm and supports a few vibrational levels. As a result the laser may be tuned over several transitions. 

Continuous transitions are characterized by a critical behavior of a physical observable, which is the order parameter y of the transition. Above the transition temperature the thermodynamic average of the order parameter is zero, indicative of complete loss of long-range order. Below Tc the value of is nonzero indicating long-range order, and follows a power law when approaching the critical temperature ... 

Indicator Concentration, % Solvent Colour change Transition range, pH... 

In general, we seek an indicator whose transition range overlaps the steepest part of Choose an indicator whose transition range... 

Hammett acidity function indicator error transition range... 

Choosing an indicator Color transition range should match pH at Ve. Preferably the color change should occur entirely within the steep portion of the titration curve. 

Would the indicator bromocresol green, with a transition range of pH 3.8—5.4, ever be useful in the titration of a weak acid with a strong base ... 

Fig. 18. (a) The temperature dependence of the free energy change for the RNase transition at different pH values. The points represent AF° values calculated from the data. The solid curves are the best fit to a quadratic equation by least squares analysis. The dashed lines indicate the range of relatively high experimental accuracy, (b) The values of AH°, AS", and ACP for the RNase transition from data at pH 2.50. Reproduced from Brandts and Hunt (336). 

Transition range, pH Indicator CAS no. Color change Composition of indicator solution, %... 

Individual pH Indicators. The most commonly used pH indicators include azo dyes, nitrophenols, phthaleins, and sulfophthaleins. Varying the substituents on the chromophores yields pH indicators with different transition ranges, and the complete pH range between 0 and 14 can thus be covered, as shown in Table 5.17 and Figure 5.2. Introducing acid groups (sulfo or carboxyl) leads to water-soluble indicator dyes. 

Indicator Mixtures (Two-Component). An important criterion for the selection of an indicator is an transition interval which is clear, visually well detectable, and as sharp as possible. Ideally, the acidic and the alkaline forms should possess complementary colors, for example, red and green. Unfortunately, no individual indicator fulfills all these requirements. Furthermore, the mixture of colors in the transition range often deteriorates the quality of color change. 

Second, indicators with similar transition ranges can be combined to form a mixed indicator (Table 5.19). 

Indicator Mixtu res (Multic omponent). Mixing several indicators of different transition ranges leads to universal indicators which can be used over a wide pH range. Table 5.20 lists examples of such indicators. 

The key point in this method is the determination of the critical load where first irreversible cracks or fractures are generated and which therefore indicates the transition from plastic deformation to significant/lasting damages. For that, the normal load is constantly increased and indentation depth and tangential load are simultaneously recorded. The transition from plastic deformation to the fracture range is indicated e.g. by unsteadiness or fluctuations in the detected load flow and the indentation depth. This transition range can also be evaluated by additional... 

Orthophosphoric Acid may be titrated with sodium or potassium hydroxide free from carbonate. The equivalent point indicating NaH2P04 occurs at pH = ca. 4-2, which is within the transition range of methyl yellow, methyl orange and bromophenol blue. The endpoint tint should be matched against that of a comparison solution containing about the same concentration of NaH2P04. 

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