Acid-base Indicator

Question

Phenolphthalein is suitable indicator for titration of:

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1. **Indicator Range**: Phenolphthalein is a basic indicator with a $pH$ transition range of approximately $8.2\u201310.0$.
2. **Equivalence Point**: In a titration of a **weak acid** ($e.g.,$ Acetic acid) with a **strong base** ($e.g.,$ $NaOH$), the resulting salt undergoes anionic hydrolysis.
3. **Resulting pH**: This hydrolysis makes the solution slightly basic ($pH > 7$) at the equivalence point.
4. **Selection**: Since the equivalence point $pH$ (typically around $8\u20139$) falls within the color-change range of phenolphthalein, it is the ideal indicator.
5. **Contrast**: For a strong acid vs weak base titration, the equivalence point is acidic ($pH < 7$), making Methyl Orange (range $3.1\u20134.4$) a better choice.

Acid-base Indicator

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