Indicators are substances whose solutions change color due to changes in pH. These are called acid-base indicators.
They are usually weak acids or bases, but their conjugate base or acid forms have different colors due to differences in their absorption spectra.
Name | Acid Color | pH Range of Color Change | Base Color |
---|---|---|---|
Methyl violet | Yellow | 0.0 - 1.6 | Blue |
Thymol blue | Red | 1.2 - 2.8 | Yellow |
Methyl orange | Red | 3.2 - 4.4 | Yellow |
Bromocresol green | Yellow | 3.8 - 5.4 | Blue |
Methyl red | Red | 4.8 - 6.0 | Yellow |
Litmus | Red | 5.0 - 8.0 | Blue |
Bromothymol blue | Yellow | 6.0 - 7.6 | Blue |
Thymol blue | Yellow | 8.0 - 9.6 | Blue |
Phenolphthalein | Colorless | 8.2 - 10.0 | Pink |
Thymolphthalein | Colorless | 9.4 - 10.6 | Blue |
Alizarin yellow R | Yellow | 10.1 - 12.0 | Red |