Visualization method color change

In a titrimetric method of analysis the volume of titrant reacting stoichiometrically with the analyte provides quantitative information about the amount of analyte in a sample. The volume of titrant required to achieve this stoichiometric reaction is called the equivalence point. Experimentally we determine the titration s end point using a visual indicator that changes color near the equivalence point. Alternatively, we can locate the end point by recording a titration curve showing the titration reaction s progress as a function of the titrant s volume. In either case, the end point must closely match the equivalence point if a titration is to be accurate. Knowing the shape of a titration... 

By this method the weighed dry product is dissolved in methanol and titrated with the Karl Fischer solution until the color changes from brown to yellow. The visual observation can be replaced by an ammeter, which shows an steep increase in current, when the titration is terminated (dead-stop-titration). The samples can be two to four times smaller than for the gravimetric method. To avoid the visual observation completely, iodine can be produced by electrolyzation and the water content is calculated by Coulomb s law. Such an apparatus (e. g. Fig. 1.97.1 and 1.97.2) is available commercially. The smallest amount of water to be detected by such instruments is 10 pg. Wekx and De Kleijn [1.84) showed, how the Karl Fischer method can be used directly in the vial with the dried product. The Karl... 

By this method the weighed dry product is dissolved in methanol and titrated with Karl Fischer solution until the color changes from brown to yellow. The visual observation can be replaced by an ammeter, which shows a steep increase in current when the end-point of the titration is reached (dead-stop titration). The samples can be two to four times smaller than for the gravimetric method. To avoid the visual observa-... 

Absorption spectrometry is a traditional method used for the measurement of various chemical substances and makes it possible to carry out visual colorimetry allowing easy measurements. Conventional absorption spectrophotometry is the measurement of numerical values such as that of absorbance to carry out qualitative and quantitative analysis. In such cases, if the spectra obtained are complicated, the determination often becomes difficult. However, even if the spectral changes are quite complicated, our eyes recognize them simply as color changes. Determination utilizing the colors themselves is a perceptual method instead of simple absorption spectrophotometry. 

TheNafion-H given above exhibits acidic character comparable to 100% H2S04. The physical and chemical properties of the resins as reported by the manufactures are summarized in Table IV (55). It has been suggested that Nafion-H has an acidity between -11 and - 13 (8, 9), and we also determined it to be -12 by the visual color change method of the... 

Acid strength of the Hf02 catalysts could not be measured by the visual color change method of Hammett indicators because the materials change color (to yellow) after calcination. The maximum activity was observed with calcination at 700°C, and its catalytic activity for the reaction of butane was close to that of the Zr02-I (650°C) catalyst. Thus, the catalyst treated at 700°C is considered to hold the acid strength close to Ho = - 16 on the surface (138). The superacid of Fe203 is also colored (brown) it is... 

Methods in which the escaping nitrous gases can be recognized visually or by noting the color change of a strip of dyed filter paper. The former methods include the qualitative tests at 132, 100, 75, and 65.5 °C (270, 212, 167, and 150 °F). These tests include the U.S. supervision test, the methyl violet test, the Abel test, and the Vieille test. 

In order to determine the equivalence point (the point at which exactly stoichiometric quantities of sample and titrant have been brought together), it is necessary to find a chemical or physical property that changes very rapidly at this point. Many properties have been used successfully, but the most common method is the visual observation of a color change in a chemical indicator present in very small concentration. This observable change takes place at the end point, which must lie very close to the equivalence point. The technique of titration is concerned principally with approaching the end point with reasonable speed without running over it is best learned by practice, but there are descriptions in the literature that may be helpful. 

The acid strengths shown in Table 17.3 were examined by the visual color change method using the Hammett indicators shown in Table 17.1 [43, 48]. The indicator dissolved in solvent was added to the sample in powder form in a nonpolar solvent, sulfuryl chloride [38] or cyclohexane [40]. The strength of colored materials such as S04/Fe203 and Mo03/Zr02 was estimated from their catalytic activities in comparison with those of the catalysts determined by the Hammett-indicator method. 

Color Charts. The colors of pigments can be routinely measured by visual comparison with color charts like the one issued by the Munsell Color Company. This method may achieve a high precision because of the eye s sensitivity to small (relative) color changes. Of paramount importance for reliable application is a uniform light source. The major drawback of the method is that the resolution of color assignments is limited by the resolution of the color chips (see 3.2.3). Interpolation between chips is possible in principle, but difficult in practice as it has to be done in a three-dimensional space. 

Spectrophotometric Methods Measurement of UV/visible absorption can also be used to detennine the end points of titrations (see Section 26A-4). In these cases, an instrument responds to the color change in the titration rather than relying on a visual detennination of the end point. 

Free water in jet fuels can be detected by the use of the Karl Fischer titration method (ASTM D-1744) or by observing color changes when chemicals go into aqueous solution (ASTM D-3240). The standard water reaction test for jet fuel (ASTM D-1094, IP 289) is the same as for aviation gasoline, but the interface and separation ratings are more critically defined. Test assessment is by subjective visual observation and, although quite precise when made by an experienced operator, the test can cause rating difficulties under borderline conditions. As a consequence, a more objective test, known as the water separometer test, is now included in many specifications (ASTM D-2550). 

Titrimetric luminescence methods record changes in the indicator emission of radiation during titration. This change is noted visually or by instruments normally used in luminescence analysis. Most luminescence indicators are complex organic compounds which are classified into fluorescent and chemiluminescent, compounds according to the type of emission of radiation. As in titrimetry with adsorption of colored indicators, luminescence titration makes use of acid-base, precipitation, redox, and complexation reactions. Unlike color reactions, luminescence indicators enable the determination of ions in turbid or colored media and permit the detection limit to be lowered by a factor of nearly one thousand. In comparison with direct luminescence determination, the luminescence titrimetric method is more precise. 

All the methods described are invasive techniques that are time consuming and often expensive. To reduce sampling and analytical costs, and to speed up the analyses, noninvasive analytical procedures have been developed with the aims to characterize the pigment content of samples and, in the case of food products, to estimate the impact of a color change on the visual perception of the product. 

Photoelectric colorimeters and spectrophotometers are in general use for the determination of decolorizing properties, especially when many samples are to be evaluated. Although direct visual methods are less convenient and subject to considerable personal equation, they have a virtue in that they immediately reveal changes in the hue and shade of color—features that can disclose significant aspects. Visual observation is helpful to ensure that the filtrates are completely free of carbon particles or other turbidity. 

The blue dye-was less adsorbable than the red dye consequently the filtrate from a treatment with activated carbon had a bluish color that did not match any dilution of the original solution. The change in hue was disclosed in visual methods of testing, for example, in Nessler tubes, but it was difficult to assign a definite numerical value to the change by such visual methods of observation. 

A coulometric titration, like a more conventional volumetric procedure, requires some means of detecting the point of chemical equivalence. Most of the end-point detection methods applicable to volumetric analysis are equally saiisfactory here. Visual observations of color changes of indicators, as well as poicn-tionieiric, amperometric, and photometric measurements have all been used successfully. 

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