Acid-base Indicator
Mediumchemistry
Phenolphthalein is suitable indicator for titration of:
Select the correct option:
Solution
Incorrect! Answer:
Weak acid vs strong base
- Indicator Range: Phenolphthalein is a basic indicator with a pH transition range of approximately 8.22˘01310.0.
- 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.
- Resulting pH: This hydrolysis makes the solution slightly basic (pH>7) at the equivalence point.
- Selection: Since the equivalence point pH (typically around 82˘0139) falls within the color-change range of phenolphthalein, it is the ideal indicator.
- Contrast: For a strong acid vs weak base titration, the equivalence point is acidic (pH<7), making Methyl Orange (range 3.12˘0134.4) a better choice.
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About This Question
- Subject
- chemistry
- Chapter
- practical chemistry
- Topic
- acid-base indicator
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Weak acid vs strong base
- Indicator Range: Phenolphthalein is a basic indicator with a pH transition range of approximately 8.22˘01310.0.
- 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.
- Resulting pH: This hydrolysis makes the solution slightly basic (pH>7) at the equivalence point.
- Selection: Since the equivalence point pH (typically around 82˘0139) falls within the color-change range of phenolphthalein, it is the ideal indicator.
- Contrast: For a strong acid vs weak base titration, the equivalence point is acidic (pH<7), making Methyl Orange (range 3.12˘0134.4) a better choice.
This medium difficulty chemistry question is from the chapter practical chemistry, covering the topic of acid-base indicator. It appeared in the 2025 exam.
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