Question:
All of the following acids dissociate completely in water, except :
All of the following acids dissociate completely in water, except :
Show Hint
Strong mineral acids like HCl, \(\text{HNO}_3\), and \(\text{H}_2\text{SO}_4\) dissociate completely in water.
Organic acids containing the carboxyl group (--COOH), such as acetic acid and citric acid, are always weak acids that dissociate only partially.
Organic acids containing the carboxyl group (--COOH), such as acetic acid and citric acid, are always weak acids that dissociate only partially.
Updated On: Jul 13, 2026
- HCl
- \(\text{H}_2\text{SO}_4\)
- \(\text{CH}_3\text{COOH}\)
- \(\text{HNO}_3\)
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Question:
The question asks to identify which of the given acids does not dissociate completely in water, which is equivalent to identifying the weak acid from the list.
Step 2: Key Formula or Approach:
Acids are categorized based on their degree of ionization in aqueous solution:
- Strong acids: Ionize or dissociate completely into their constituent ions in water (\(\alpha \approx 100\%\)).
- Weak acids: Dissociate only partially in water, establishing a dynamic equilibrium between ionized and unionized molecules (\(\alpha \ll 100\%\)).
Step 3: Detailed Explanation:
• Let us evaluate each option:
- (A) HCl (Hydrochloric acid): A strong mineral acid that dissociates completely in water to release hydrogen ions:
\[ \text{HCl(aq)} \to \text{H}^+\text{(aq)} + \text{Cl}^-\text{(aq)} \] - (B) \(\text{H}_2\text{SO}_4\) (Sulfuric acid): A strong diprotic mineral acid that dissociates completely in dilute solutions.
- (C) \(\text{CH}_3\text{COOH}\) (Acetic acid): A weak organic carboxylic acid. In water, only a small fraction (typically less than \(5\%\)) of its molecules dissociate to form hydronium and acetate ions:
\[ \text{CH}_3\text{COOH(aq)} \rightleftharpoons \text{CH}_3\text{COO}^-\text{(aq)} + \text{H}^+\text{(aq)} \] This partial dissociation makes it a weak electrolyte.
- (D) \(\text{HNO}_3\) (Nitric acid): A strong mineral acid that dissociates completely in water.
• Thus, acetic acid is the only weak acid in the list that does not dissociate completely.
Step 4: Final Answer:
The acid that does not dissociate completely is \(\text{CH}_3\text{COOH}\).
The question asks to identify which of the given acids does not dissociate completely in water, which is equivalent to identifying the weak acid from the list.
Step 2: Key Formula or Approach:
Acids are categorized based on their degree of ionization in aqueous solution:
- Strong acids: Ionize or dissociate completely into their constituent ions in water (\(\alpha \approx 100\%\)).
- Weak acids: Dissociate only partially in water, establishing a dynamic equilibrium between ionized and unionized molecules (\(\alpha \ll 100\%\)).
Step 3: Detailed Explanation:
• Let us evaluate each option:
- (A) HCl (Hydrochloric acid): A strong mineral acid that dissociates completely in water to release hydrogen ions:
\[ \text{HCl(aq)} \to \text{H}^+\text{(aq)} + \text{Cl}^-\text{(aq)} \] - (B) \(\text{H}_2\text{SO}_4\) (Sulfuric acid): A strong diprotic mineral acid that dissociates completely in dilute solutions.
- (C) \(\text{CH}_3\text{COOH}\) (Acetic acid): A weak organic carboxylic acid. In water, only a small fraction (typically less than \(5\%\)) of its molecules dissociate to form hydronium and acetate ions:
\[ \text{CH}_3\text{COOH(aq)} \rightleftharpoons \text{CH}_3\text{COO}^-\text{(aq)} + \text{H}^+\text{(aq)} \] This partial dissociation makes it a weak electrolyte.
- (D) \(\text{HNO}_3\) (Nitric acid): A strong mineral acid that dissociates completely in water.
• Thus, acetic acid is the only weak acid in the list that does not dissociate completely.
Step 4: Final Answer:
The acid that does not dissociate completely is \(\text{CH}_3\text{COOH}\).
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