Question:
The acid which has the highest ionization constant ($K_a$) at $298,K$ is
The acid which has the highest ionization constant ($K_a$) at $298,K$ is
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Chemistry Tip: Larger $K_a$ means stronger acid, while smaller $pK_a$ means stronger acid.
Updated On: Apr 27, 2026
- HNO$_2$
- C$_6$H$_5$OH
- HClO
- C$_5$H$_4$NCOOH
- HF
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The Correct Option is A
Solution and Explanation
Concept:
Higher ionization constant $K_a$ means stronger acid. Stronger acid $\Rightarrow$ greater tendency to donate $H^+$ ions.
Step 1: Compare given acids qualitatively.
- Phenol (C$_6$H$_5$OH) is very weak acid. - HF is weak acid. - HClO is weak oxyacid. - Pyridine carboxylic acid is moderate weak acid. - HNO$_2$ (nitrous acid) is comparatively stronger among these.
Step 2: Relative strengths.
Approximate order: $$\text{HNO}_2>\text{HF}>\text{carboxylic acid variants}>\text{HClO}>\text{phenol}$$ Thus highest $K_a$ belongs to HNO$_2$.
Step 3: Final answer.
Hence correct option is (A). :contentReference[oaicite:1]{index=1}
Higher ionization constant $K_a$ means stronger acid. Stronger acid $\Rightarrow$ greater tendency to donate $H^+$ ions.
Step 1: Compare given acids qualitatively.
- Phenol (C$_6$H$_5$OH) is very weak acid. - HF is weak acid. - HClO is weak oxyacid. - Pyridine carboxylic acid is moderate weak acid. - HNO$_2$ (nitrous acid) is comparatively stronger among these.
Step 2: Relative strengths.
Approximate order: $$\text{HNO}_2>\text{HF}>\text{carboxylic acid variants}>\text{HClO}>\text{phenol}$$ Thus highest $K_a$ belongs to HNO$_2$.
Step 3: Final answer.
Hence correct option is (A). :contentReference[oaicite:1]{index=1}
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