Acid-Base Indicators
| Indicator | pH Range | pKa | Colors* |
|---|---|---|---|
| Cresol red | 0.2 to 1.8 | 1.0 | R-Y |
| Thymol blue | 1.2 to 2.8 | 1.65 | R-Y |
| Methyl yellow | 2.9 to 4.0 | 3.3 | R-Y |
| Methyl orange | 3.1 to 4.4 | 3.4 | R-O |
| Bromophenol blue | 3.0 to 4.6 | 3.85 | Y-B |
| Bromocresol green | 4.0 to 5.6 | 4.7 | Y-B |
| Methyl red | 4.4 to 6.2 | 4.95 | R-Y |
| p-Nitrophenol | 5.3 to 7.6 | 7.2 | C-Y |
| Phenol red | 6.4 to 8.0 | 7.9 | Y-R |
| Thymol blue | 8.0 to 9.6 | 8.9 | Y-B |
| Phenolphthalein | 8.0 to 10.0 | 9.4 | C-R |
| Alizarin yellow R | 10.0 to 12.0 | 11.2 | Y-V |
* B = blue, C = colorless, O = orange, R = red, V = violet, Y = yellow
Reference: C.A. Streuli, in "Handbook of Analytical Chemistry," L. Meites, Ed., McGraw-Hill, NY, 1963, pps. 3-35 and 3-36.