Compounds that change color when exposed to acidic or basic solutions are known as indicators. Color indicators are widely used to detect pH and can be added to the reaction mixture to determine the titration endpoint or equivalence point.
A variety of indicators are used in different types of titrations, including acid-base, redox, precipitation, and complexometric. Each has its pKa, pH range, and produces a different color at different pH levels.
Table of Contents: 1. Acid base indicators 2. Metal indicators 3. Non aqueous indicators 4. Redox indicators 5. Adsorption and miscellaneous indicators |
In chemistry, there are three types of indicators: natural indicators, artificial indicators, and olfactory indicators, while artificial and natural indicators are the two most commonly used forms.
Here are some common indicators are listed in table form along with their pH range, and color change under acidic, basic, and neutral environments.
List of indicators used in acid-base
titration:
Name of Indicator | Useful pH Range | Color Change |
---|---|---|
Bromocresol Green | 3.6 to 5.2 | Yellow to blue |
Bromocresol Purple | 5.2 to 6.8 | Yellow to bluish-violet |
Bromophenol Blue | 2.8 to 4.6 | Yellow to bluish-violet |
Bromothymol Blue | 6.0 to 7.6 | Yellow to blue |
m-Cresol | 1.2 to 2.8 and 7.6 to 9.2 | Red to yellow and yellow to violet |
Cresol Red | 0.2 to 1.8 and 7.2 to 8.8 | Red to yellow and yellow to violet-red |
Dimethyl Yellow | 2.8 to 4.6 | Red to yellow |
2-4 Dinitrophenol | 2.8 to 4.4 | Colorless to yellow |
Methyl Orange | 2.9 to 4.6 | Red to yellow |
Methyl Red | 4.2 to 6.3 | Red to yellow |
1-Naphtholphthalein | 7.3 to 8.7 | Pale red to blue |
3-Nitrophenol | 6.8 to 8.4 | Colorless to yellow |
4-Nitrophenol | 5.0 to 7.0 | Colorless to yellow |
Phenolphthalein | 8.3 to 10.0 | Colorless to red/pink |
Phenol Red | 6.8 to 8.4. | Yellow to red |
Thymol Blue | 1.2 to 2.8 and 8.0 to 9.6 | Red to yellow and to violet-blue |
Thymolphthalein | 8.3 to 10.5 | Colorless to blue |
List of common metal indicators used in complexometric titration:
Name of Indicator | Useful pH Range | Color Change |
---|---|---|
Calcein | - | Orange-yellow to yellowish red |
Calcon | - | Purple red to pure blue |
Catechol Violet | 0.0 to 8.0 | Blue/red to yellow |
Dithizone | - | Pink to green |
Methyl-thymol Blue | 4.0 to 10.0 | Red to yellow to blue |
Mordant Black II | 7.0 to 11.0 | Blue to pink |
Murexide | 6.0 to 13.0 | Yellow to reddish-purple to blue-purple |
Pyridylazonaphthol | - | Yellow to Red |
Sodium Alizarin Sulphonate | 3.7 to 5.2 | Bluish-red to yellow |
Thoron | - | Red to yellow |
Xylenol orange | 6.4 to 10.4 | Yellow to orange-red |
List of common indicators used in non-aqueous titrations:
Name of Indicator | Useful pH Range | Color Change |
---|---|---|
Alkali Blue 6B | 9.4 to 14 | Red to Blue |
Crystal Violet | 0.0 to 2.0 | Violet (basic), to bluish-green (neutral) to yellowish green (acidic) |
1-Naphtholbenzein | 8.2 to 10.0 | Green (basic) to orange (neutral) to yellow (acidic) |
Quinaldine Red | 1.0 to 2.2 | Magenta to colorless. |
List of common indicators used in oxidation and reduction (Redox) titrations:
Name of Indicator | E0, V | Color of oxidized and reduced form |
---|---|---|
Potassium permanganate (KMnO4) | 1.51 V | Purple to colorless |
Crystal Violet | 0.0 to 2.0 | Violet (basic), to bluish-green (neutral) to yellowish green (acidic) |
1,10-Phenanthroline iron(II) sulfate complex (Ferroin) | +1.08 V | Red to blue |
Ceric ammonium sulphate | - | Pink to very pale blue |
Phenanthroline blue | +1.06 V | Deep red to light-blue |
Methylene blue | +0.53 | Blue to colorless |
Safranin T | +0.24 | Red-violet to colorless |
Barium Diphenylamine-4-Sulphonate | +0.84 V | Colorless to violet |
Indigo carmine | +0.29 | Blue to colorless |
List of common indicators used in adsorption and miscellaneous:
Name of Indicator | Useful pH Range | Color Change |
---|---|---|
Amaranth | - | Orange-red to yellow |
Dicblorofluorescein | 5 to 8 | Precipitate orange to pink |
Starch | - | Colorless to blue |
Potassium chromate | 6.5 to 10.5 | Yellow to reddish brown |
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