An indicator is a substance that changes color when exposed to acidic or basic conditions. To determine the endpoints of acid-base titration, we employ phenolphthalein and methyl orange as indicators.
The selection of a certain indicator for titration is decided based on a plot known as the pH curve, which is typical of a specific reaction. The dissociation of the H+ ion from the indicator causes a pH indicator's colour to change. In the flask, the indicator is always added to the reactant.
What is the color of phenolphthalein and methyl orange in the acidic and basic and neutral medium?
- Methyl orange produces a red color in acidic solutions, whereas yellow color in basic solutions.
- Phenolphthalein is colorless in acidic solutions, whereas process pink color in basic solutions.
| Color of phenolphthalein in acid | Colourless |
| Color of phenolphthalein in base | Pink |
| Color of phenolphthalein in neutral | Colourless |
Color change of methyl orange:
| Colour of methyl orange in acid | Red |
| Colour of methyl orange in base | Yellow |
| Colour of methyl orange in neutral | Yellow |
In an acid-base titration, different types of indicators are used; however, depending on the pH range, phenolphthalein and methyl orange are the most commonly used indicators. Phenolphthalein has a pH range of 8.3 to 10.0, while that of methyl orange is 3.1 to 4.4.
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