Question:
Which of the following acids is not a polyprotic acid?
Which of the following acids is not a polyprotic acid?
Show Hint
To identify polyprotic organic acids, look for multiple carboxylic groups ($-\text{COOH}$).
Monocarboxylic acids like formic acid ($\text{HCOOH}$) and acetic acid ($\text{CH}_3\text{COOH}$) are always monoprotic, as only the carboxylic proton can dissociate.
Monocarboxylic acids like formic acid ($\text{HCOOH}$) and acetic acid ($\text{CH}_3\text{COOH}$) are always monoprotic, as only the carboxylic proton can dissociate.
Updated On: Aug 7, 2026
- Chromic acid
- Malonic acid
- Carbonic acid
- Formic acid
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Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Acids are classified based on the number of ionizable hydrogen atoms (protons) they can donate per molecule in an aqueous solution.
A monoprotic acid can donate only one proton, whereas a polyprotic (including diprotic and triprotic) acid can donate two or more protons in successive ionization steps.
Step 2: Detailed Explanation:
Let us analyze the chemical structure and ionization behavior of each of the listed acids:
1. Chromic acid ($\text{H}_2\text{CrO}_4$): A diprotic mineral acid that dissociates in two steps, releasing two protons per molecule.
2. Malonic acid ($\text{CH}_2(\text{COOH})_2$): A dicarboxylic organic acid containing two carboxylic acid functional groups, allowing it to release two protons.
3. Carbonic acid ($\text{H}_2\text{CO}_3$): A weak diprotic inorganic acid that undergoes step-wise dissociation to form bicarbonate ($\text{HCO}_3^-$) and carbonate ($\text{CO}_3^{2-}$) ions, releasing two protons.
4. Formic acid ($\text{HCOOH}$): The simplest carboxylic acid. Although it contains two hydrogen atoms in its molecular formula, only the hydrogen atom covalently bonded to the electronegative oxygen atom is ionizable.
The hydrogen atom bonded directly to the carbon atom is non-acidic and cannot dissociate.
Therefore, formic acid is a monoprotic acid.
Step 3: Final Answer:
Formic acid is not a polyprotic acid, which corresponds to Option (D).
Acids are classified based on the number of ionizable hydrogen atoms (protons) they can donate per molecule in an aqueous solution.
A monoprotic acid can donate only one proton, whereas a polyprotic (including diprotic and triprotic) acid can donate two or more protons in successive ionization steps.
Step 2: Detailed Explanation:
Let us analyze the chemical structure and ionization behavior of each of the listed acids:
1. Chromic acid ($\text{H}_2\text{CrO}_4$): A diprotic mineral acid that dissociates in two steps, releasing two protons per molecule.
2. Malonic acid ($\text{CH}_2(\text{COOH})_2$): A dicarboxylic organic acid containing two carboxylic acid functional groups, allowing it to release two protons.
3. Carbonic acid ($\text{H}_2\text{CO}_3$): A weak diprotic inorganic acid that undergoes step-wise dissociation to form bicarbonate ($\text{HCO}_3^-$) and carbonate ($\text{CO}_3^{2-}$) ions, releasing two protons.
4. Formic acid ($\text{HCOOH}$): The simplest carboxylic acid. Although it contains two hydrogen atoms in its molecular formula, only the hydrogen atom covalently bonded to the electronegative oxygen atom is ionizable.
The hydrogen atom bonded directly to the carbon atom is non-acidic and cannot dissociate.
Therefore, formic acid is a monoprotic acid.
Step 3: Final Answer:
Formic acid is not a polyprotic acid, which corresponds to Option (D).
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