Acid and Base pH Indicators (original) (raw)
pH range vs. color change for acid and base indicators - together with pKa and structures of the indicators.
The ranges for the color changes are given in the table below the figure, together with the corresponding pKa value of the indicators.
Acid and Base pH Indicators
| Trade name | pH start | pH end | pKa | low pH color | high pH color |
|---|---|---|---|---|---|
| Cresol red - step 1 | 0.2 | 1.8 | 1.0 | red | yellow |
| Malachite green -step 1 | 0.2 | 1.8 | 1.3 | yellow | green |
| Thymol blue - step 1 | 1.2 | 2.8 | 1.7 | red | yellow |
| Methyl yellow | 2.9 | 4.0 | 3.3 | red | yellow |
| Methyl orange | 3.1 | 4.4 | 3.5 | red | yellow |
| Bromophenol blue | 3.0 | 4.6 | 4.1 | yellow | blue |
| Congo red | 3.0 | 5.0 | blue-violet | red | |
| Methyl orange in xylene cyanol (screened) | 3.2 | 4.2 | grey-violet | green | |
| Bromocresol green | 3.8 | 5.4 | 4.7 | yellow | blue |
| Methyl red | 4.4 | 6.2 | 5.1 | red | yellow |
| Methyl purple | 4.8 | 5.4 | purple | green | |
| Bromocresol purple | 5.2 | 6.8 | 6.4 | yellow | purple |
| Azolitmin (litmus) | 4.5 | 8.3 | red | blue | |
| Bromothymol blue | 6.0 | 7.6 | 7.3 | yellow | blue |
| Phenol red | 6.4 | 8.0 | 8.0 | yellow | red |
| Neutral red | 6.8 | 8.0 | red | yellow | |
| Cresol red -step 2 | 7.2 | 8.8 | 8.5 | yellow | reddish-purple |
| Naphtholphthalein | 7.3 | 8.7 | pale red | greenish-blue | |
| Thymol blue - step 2 | 8.0 | 9.6 | 9.2 | yellow | blue |
| Cresolphthalein | 8.2 | 9.8 | colorless | purple | |
| Phenolphthalein | 8.3 | 10.0 | 9.5 | colorless | red-pink |
| Thymolphthalein | 9.0 | 10.5 | 9.2 | colorless | blue |
| Alizarin yellow R | 10.1 | 12.0 | 11.2 | yellow | red |
| Indigo carmine | 11.4 | 13.0 | blue | yellow | |
| Malachite green -step 2 | 11.5 | 13.2 | green | colorless |
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