Bromocresol green, acid-base transitions

The most common acid-base indicators are either azo dyes for example, methyl orange and methyl red nitrophenols phthaleins such as phenol-phthalein or thymolphthalein or sulfonephthaleins like bromophenol blue or bromocresol green. Acid-base indicators are available that cover visual transitions usually expressed in intervals of 2 pH units ranging from pH 0.0 to 2.0 in small increments up to pH 12.0-14.0. 

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 ... 

The indicators were obtained from Kodak Laboratory Chemicals, Aldrich Chemical Company, and J.T. Baker and were used without further purification. The indicators employed in the majority of the titrations were bromocresol green and bromothymol blue each of which exhibits two acid-base transitions at Pka = -3.7, +4.6, and -1.5, +6.8, respectively(20, 22, 26) The medium for the titration and electrophoretic mobility experiments was benzene (Burdick and Jackson Laboratories) having a water content of less than 0.03 percent. The base used as titrant was n-butylamine, Baker analyzed reagent grade. 

Spraying with a 0.01-1% aqueous or aqueous alcohol solution of an acid-base indicator (e.g., bromocresol green, bromothymol blue, bromophenol blue, methyl red, malachite green) can detect acid or basic compounds on the layer based on a change in color at the location of the zones and knowledge of the pH transition range of the indicator. 

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See also in sourсe #XX -- [ ]

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