Methyl Yellow

Methyl yellow, p-dimethylaminoazobenzene, benzeneazodimethylaniline (indicator) dissolve 0.1 g in 200 mL alcohol pH range red 2.9-4.0 yellow. The color change from yellow to orange can be perceived somewhat more sharply than the change of methyl orange from orange to rose, so that methyl yellow seems to deserve preference in many cases. See also under methyl orange. 

Methyl yellow, neutral red, and Congo red. Dissolve 1 g of the indicator in 1 L of 80 per cent ethanol. Congo red may also be dissolved in water. 

By mixing suitable indicators together changes in colour may be obtained over a considerable portion of the pH range. Such mixtures are usually called universal indicators . They are not suitable for quantitative titrations, but may be employed for the determination of the approximate pH of a solution by the colorimetric method. One such universal indicator is prepared by dissolving 0.1 g of phenolphthalein, 0.2 g of methyl red, 0.3 g of methyl yellow, 0.4 g of... 

The pH at the equivalence point is thus approximately 3.7 the secondary ionisation and the loss of carbonic acid, due to any escape of carbon dioxide, have been neglected. Suitable indicators are therefore methyl yellow, methyl orange, Congo red, and bromophenol blue. The experimental titration curve, determined with the hydrogen electrode, for 100 mL of 0.1 M sodium carbonate and 0.1M hydrochloric acid is shown in Fig. 10.7. 

The pH range for bases with Kb> 10 5 is 3-7, and for weaker bases (Kb > 10 6) 3-5. Suitable indicators will be methyl red, methyl orange, methyl yellow, bromocresol green, and bromophenol blue. 

Kato, T.-A., Matsuda, T., Matsui, S., Mizutani, T. and Saeki, K.-I. (2002) Activation of the aryl hydrocarbon receptor by methyl yellow and related congeners structure-activity relationships in halogenated derivatives. Biological e[ Pharmaceutical Bulletin, 25, 466 171. 

Dissolve 60 mg methyl yellow, 40 mg methyl red, 80 mg bromthymol blue, 100 mg thymol blue and 20 mg phenolphthalein in 100 ml of ethanol and add enough 0.1 AT NaOH to produce a yellow color. 

Take the burette reading as R,. Add 5 drops of methyl-yellow indicator and titrate to the first slight indication of change of color from yel to reddish. This occurs when all bicarbonate is converted to sulfate. Take the burette reading as Ra Calculations ... 

It should be noted that if a solid tech Na azide is used as a starting material for the above test it is necessary to remove the carbonates prior to adding NaN02. This can be done by dissolving the sample in distd w and neutralizing the soln with HCl, using methyl-orange, methyl-yellow or equivalent rest paper... 

Methyl yellow indicator 0.1% (w/v) p-dimethylaminoazobenzene in absolute ethanol... 

Add 0.2 ml methyl yellow indicator. Titrate with 0.5 N p-toluenesulfonic acid to an endpoint of pH 3.5. 

Effect of /3-cyclodc trin on cis trans isomerization of azobenzenes was studied by Sanchez and de Rossi [26], It was found that the cis-trans thermal isomerization of / -Mcthvl Red, o-Methyl Red and Methyl Orange is inhibited by fi-CD at constant pH. The isomerization rate decreases 4, 8, and 1.67 times, respectively, in a solution containing 0.01 M /J-CD. This effect was attributed to the formation of inclusion complexes hindering rotation of the -N=N- bond. Isomerization of Methyl Yellow and naphthalene-l-azo-[4 -(dimethylamino)benzene] requiring mixed organic-aqueous... 

N,N-Dimethyl-4-(phenylazo)benzenimine, butter yellow, methyl yellow, solvent yellow 2, Cl 11020. 

These constants determine the titration exponents pH and the best indicators for the successive hydrions. The acid can be titrated as dibasic, using methyl yellow, methyl orange or bromophenol blue, and as tetrabasic using phenolphthalein, thymolphthalein or thymol blue in the presence of a moderate excess of soluble barium salt. The values of pH in the partly neutralised acid were corrected for the salt error, and the constants Kz and jfiT4 which prevail in solutions of low concentration were thus deduced —6... 

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