The Useful pH Ranges for Several Common Indicators
The useful pH ranges for several common indicators are shown including their observed colors. The pH ranges shown are approximate and vary with solvent composition. Note that most indicators have a useful range of about two pH units, as predicted by the expression pKa ± 1. Data are available in the adjacent table.
| Indicator Name | Primary Range | Secondary Range | ||||||
|---|---|---|---|---|---|---|---|---|
| low-end pH | low-end color | high-end pH | high-end color | low-end pH | low-end color | high-end pH | high-end color | |
| Crystal Violet | 0 | yellow | 1.8 | blue | ||||
| Cresol Red | 1.0 | red | 2.0 | yellow | 7.0 | yellow | 8.8 | orange |
| Thymol Blue | 1.2 | red | 2.7 | yellow | 8.0 | yellow | 9.1 | blue |
| Erythrosin B | 2.2 | orange | 3.6 | red | ||||
| 2,4-Dinitrophenol | 2.6 | pale yellow | 4.0 | bright yellow | ||||
| Bromphenol Blue | 3.0 | yellow | 4.6 | blue | ||||
| Methyl Orange | 3.3 | orange | 4.5 | yellow | ||||
| Bromcresol Green | 3.8 | yellow | 5.3 | blue | ||||
| Methyl Red | 4.2 | pale pink | 6.3 | bright yellow | ||||
| Eriochrome Black T | 5.0 | red | 6.5 | bluish purple | ||||
| Bromcresol Purple | 5.2 | yellow | 6.7 | purple | ||||
| Alizarin | 5.6 | yellow | 7.2 | orange | 11.0 | red | 12.3 | deep blue |
| Bromthymol Blue | 6.0 | yellow | 8.0 | blue | ||||
| Phenol Red | 6.8 | yellow | 8.2 | red | ||||
| m-Nitrophenol | 6.8 | pale yellow | 8.4 | bright yellow | ||||
| o-Cresolphthalein | 8.2 | pale pink | 9.8 | bright pink | ||||
| Phenolphthalein | 8.1 | pale pink | 10.0 | bright pink | ||||
| Thymolphthalein | 9.5 | pale blue | 10.5 | blue | ||||
| Alizarin Yellow R | 10.0 | yellow | 11.9 | red | ||||