List of Acid-Base Indicators

Acid-base indicator is a kind of organic weak-acid or organic weak-base with a more complex structure that shows a color change as the concentration of hydrogen (H⁺) or hydroxide (OH^-) ions changes in an aqueous solution. Since the color of the indicator depends on the pH of the solution, acid-base indicators find wide use in applications that involve pH changes, such as acid-base titrations (main application), pH testing, and science demonstrations. When used as a rapid end-point indicator in an acid-base titration, the indicator undergoes a Color change at the equivalence point, allowing the user to visually recognize the endpoint of the titration, and then determining the acid or alkali content of a solution. To facilitate researchers to quickly select the most suitable indicator for their study, the common acid-base indicators and their pH range and color change are listed in below.

Table of Common Acid-Base Indicators

Indicator	pH Range	Color at Acid Condition	Color at Base Condition
Thymol Blue	1.2-2.8	Red	Yellow
Pentamethoxy red	1.2-2.3	Red-violet	Colorless
Tropeolin OO	1.3-3.2	Red	Yellow
2,4-Dinitrophenol	2.4-4.0	Colorless	Yellow
Methyl yellow	2.9-4.0	Red	Yellow
Methyl orange	3.1-4.4	Red	Orange
Bromphenol blue	3.0-4.6	Yellow	Blue-violet
Tetrabromphenol blue	3.0-4.6	Yellow	Blue
Alizarin sodium sulfonate	3.7-5.2	Yellow	Violet
α-Naphthyl red	3.7-5.0	Red	Yellow
p-Ethoxychrysoidine	3.5-5.5	Red	Yellow
Bromcresol green	4.0-5.6	Yellow	Blue
Methyl red	4.4-6.2	Red	Yellow
Bromcresol purple	5.2-6.8	Yellow	Purple
Chlorphenol red	5.4-6.8	Yellow	Red
Bromphenol blue	6.2-7.6	Yellow	Blue
p-Nitrophenol	5.0-7.0	Colorless	Yellow
Azolitmin	5.0-8.0	Red	Blue
Phenol red	6.4-8.0	Yellow	Red
Neutral red	6.8-8.0	Red	Yellow
Rosolic acid	6.8-8.0	Yellow	Red
Cresol red	7.2-8.8	Yellow	Red
α-Naphtholphthalein	7.3-8.7	Rose	Green
Tropeolin OOO	7.6-8.9	Yellow	Rose-red
Thymol blue	8.0-9.6	Yellow	Blue
Phenolphthalein	8.0-10.0	Colorless	Red
α-Naphtholbenzein	9.0-11.0	Yellow	Blue
Thymolphthalein	9.4-10.6	Colorless	Blue
Nile blue	10.1-11.1	Blue	Red
Alizarin yellow	10.0-12.0	Yellow	Lilac
Salicyl yellow	10.0-12.0	Yellow	Orange-brown
Diazo violet	10.1-12.0	Yellow	Violet
Tropeolin O	11.0-13.0	Yellow	Orange-brown
Nitramine	11.0-13.0	Colorless	Orange-brown
Poirrier's blue	11.0-13.0	Blue	Violet-pink
Trinitrobenzoic acid	12.0-13.4	Colorless	Orange-red

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