JEE MainChemistryRedox Reactions
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Phenolphthalein is the most suitable indicator for the standardisation of NaOH solution using potassium hydrogen phthalate. Reason (R) : At the equivalence point of this titration, the solution is basic due to the anionic hydrolysis of the salt formed. In the light of the above statements, choose
Options
- ABoth (A) and (R) are correct but (R) is not the correct explanation of (A)
- B(A) is correct but (R) is not correct
- CBoth (A) and (R) are correct and (R) is the correct explanation of (A)
- D(A) is not correct but (R) is correct
Correct answer
C. Both (A) and (R) are correct and (R) is the correct explanation of (A)
Step-by-step solution
Potassium hydrogen phthalate (KHP) is a weak monobasic acid, while NaOH is a strong base. During their titration, the salt formed is potassium sodium phthalate. The phthalate anion undergoes anionic hydrolysis, resulting in a basic solution at the equivalence point ( pH > 7 ). Phenolphthalein has a pH transition range of approximately 8.2 to 10.0, which coincides perfectly with the steep pH change at the equivalence point of this weak acid-strong base titration. Therefore, phenolphthalein is the most suitable indic