Acid–base Equilibria
Given Ka values: HF (6.8×10⁻⁴), HCN (6.2×10⁻¹⁰), HCOOH (1.8×10⁻⁴), Phenol (1.1×10⁻⁻⁰). Increasing order of conjugate base strength is:
Select the correct option:
Solution
F− < HCOO− < CN− < C6H5O−
- Brønsted-Lowry Rule: A strong acid has a weak conjugate base, and a weak acid has a strong conjugate base.
- Acid Strength (Ka): Larger Ka⟹ Stronger Acid.
- Ranking Acids (by Ka):
- HF (6.8×10−4) — Strongest acid
- HCOOH (1.8×10−4)
- HCN (6.2×10−10)
- Phenol (1.1×10−10) — Weakest acid
- Reversing for Conjugate Bases: The order of base strength is inversely proportional to Ka.
- Base Strength Order: F−<HCOO−<CN−<C6H5O−.
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About This Question
- Subject
- chemistry
- Chapter
- equilibrium
- Topic
- acid–base equilibria
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
F− < HCOO− < CN− < C6H5O−
- Brønsted-Lowry Rule: A strong acid has a weak conjugate base, and a weak acid has a strong conjugate base.
- Acid Strength (Ka): Larger Ka⟹ Stronger Acid.
- Ranking Acids (by Ka):
- HF (6.8×10−4) — Strongest acid
- HCOOH (1.8×10−4)
- HCN (6.2×10−10)
- Phenol (1.1×10−10) — Weakest acid
- Reversing for Conjugate Bases: The order of base strength is inversely proportional to Ka.
- Base Strength Order: F−<HCOO−<CN−<C6H5O−.
This hard difficulty chemistry question is from the chapter equilibrium, covering the topic of acid–base equilibria. It appeared in the 2025 exam.
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