Referring to the table below, select an indicator for use in the titration of C6H5NH2 (pKb=9.41) with a strong acid. Which indicator would be most appropriate?

• A. Bromothymol blue (pH range: 6.0 - 7.6)
• B. Litmus (pH range: 4.5 - 8.3)
• C. Phenolphthalein (pH range: 8.2 - 10.0)
• D. Methyl orange (pH range: 3.1 - 4.4)

Answer: (C)

Verified step by step guidance

1. Identify the type of titration: In this problem, we are titrating aniline (C6H5NH2), a weak base, with a strong acid.
2. Determine the pH at the equivalence point: For a weak base-strong acid titration, the pH at the equivalence point is less than 7. Calculate the pH using the formula: \( \text{pH} = 14 - \frac{1}{2}(\text{pKb} + \text{pKw}) \), where \( \text{pKw} = 14 \).
3. Calculate the pH at the equivalence point: Substitute the given \( \text{pKb} = 9.41 \) into the formula to find the pH at the equivalence point.
4. Select an appropriate indicator: Choose an indicator whose pH range includes the calculated pH at the equivalence point. Compare the calculated pH with the pH ranges of the given indicators.
5. Determine the most suitable indicator: Based on the comparison, select the indicator whose range best matches the calculated pH at the equivalence point. In this case, Phenolphthalein is appropriate as its range (8.2 - 10.0) includes the expected pH.