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Thymol blue (thymolsulfonephthalein) is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali solutions.
Thymolphthalein is a phthalein dye used as an acid–base indicator. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. The molar extinction coefficient for the blue thymolphthalein dianion is 38,000 M −1 cm −1 at 595 nm. [2]
Universal indicator components Indicator Low pH colour Transition pH range High pH colour Thymol blue (first transition) Red 1.2 – 2.8 Yellow Methyl orange: Red 3.2 – 4.4 Yellow Methyl red: Red 4.8 – 6.0 Yellow Bromothymol blue: Yellow 6.0 – 7.6 Blue Thymol blue (second transition) Yellow 8.0 – 9.6 Blue Phenolphthalein: Colourless
Hence, a pH indicator is a chemical detector for hydronium ions (H 3 O +) or hydrogen ions (H +) in the Arrhenius model. Normally, the indicator causes the color of the solution to change depending on the pH. Indicators can also show change in other physical properties; for example, olfactory indicators show change in their odor.
Bromothymol blue is synthesized by addition of elemental bromine to thymol blue in a solution in glacial acetic acid. [ 6 ] To prepare a solution for use as pH indicator, dissolve 0.10 g in 8.0 cm 3 N/50 (a.k.a. 0.02 Normal ) NaOH and dilute with water to 250 cm 3 .
Titration indicator table [11] Indicator name Indicator colour Transition interval (pH range) Color after high pH conditions Methyl Orange Orange/red 3.1 - 4.4 Yellow Methyl Red Red 4.4 - 6.3 Yellow Congo Red Blue 3.0 - 5.2 Red Phenolphthalein Colourless 8.3 - 10.0 Pink Thymolphthalein Colourless 9.3 - 10.5 Blue Bromophenol Blue Yellow 3.0 - 4.6
Phenolphthalein's common use is as an indicator in acid-base titrations. It also serves as a component of universal indicator, together with methyl red, bromothymol blue, and thymol blue. [3] Phenolphthalein adopts different forms in aqueous solution depending on the pH of the solution.
Phthalein dyes are a class of dyes mainly used as pH indicators, due to their ability to change colors depending on pH. [1] They are formed by the reaction of phthalic anhydride with various phenols. They are a subclass of triarylmethane dyes. Common phthalein dyes include: Bromothymol blue; Bromocresol green; Bromocresol purple; Cresol Red; o ...