Given below are two statements: Statement (I): Potassium hydrogen phthalate is a primary standard for standardisation…
Redox Reactions · Class 11 · JEE Main Previous Year Question
Given below are two statements:
Statement (I): Potassium hydrogen phthalate is a primary standard for standardisation of sodium hydroxide solution. Statement (II): In this titration phenolphthalein can be used as indicator.
In the light of the above statements, choose the most appropriate answer from the options given below:
- a✓
Both Statement I and Statement II are correct
- b
Statement I is correct but Statement II is incorrect
- c
Statement I is incorrect but Statement II is correct
- d
Both Statement I and Statement II are incorrect
Both Statement I and Statement II are correct
Step 1 — Evaluate Statement I:
Potassium hydrogen phthalate (KHP, , MW = 204.22 g/mol) is an excellent primary standard for NaOH because:
- It is available in high purity
- It is stable in air (not hygroscopic)
- It has a high molar mass (reduces weighing errors)
- It reacts stoichiometrically with NaOH:
Statement I is CORRECT ✓
Step 2 — Evaluate Statement II:
The titration of KHP (weak acid) with NaOH (strong base) produces a basic solution at the equivalence point (pH ≈ 8–9). Phenolphthalein (colour change at pH 8.3–10) is the appropriate indicator for this titration.
Statement II is CORRECT ✓
Answer: Option (1) — Both correct
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