Acid–base Equilibria

Question

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:

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1. **Brønsted-Lowry Rule**: A strong acid has a weak conjugate base, and a weak acid has a strong conjugate base.
2. **Acid Strength ($K_a$)**: Larger $K_a \implies$ Stronger Acid.
3. **Ranking Acids** (by $K_a$):
   - $HF$ ($6.8 	imes 10^{-4}$) — Strongest acid
   - $HCOOH$ ($1.8 	imes 10^{-4}$)
   - $HCN$ ($6.2 	imes 10^{-10}$)
   - $Phenol$ ($1.1 	imes 10^{-10}$) — Weakest acid
4. **Reversing for Conjugate Bases**: The order of base strength is inversely proportional to $K_a$.
5. **Base Strength Order**: **$F^- < HCOO^- < CN^- < C_6H_5O^-$**.

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Acid–base Equilibria

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