Question:
An aryl carboxylic acid on treatment with sodium hydrogen carbonate liberates a gaseous molecule. Identify the gas molecule liberated.
An aryl carboxylic acid on treatment with sodium hydrogen carbonate liberates a gaseous molecule. Identify the gas molecule liberated.
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Carboxylic acids react with sodium bicarbonate to release \(CO_2\) gas. This reaction is a standard laboratory test for identifying the \(-COOH\) group.
Updated On: Jun 22, 2026
- \(H_2\)
- \(CO_2\)
- \(CO\)
- \(O_2\)
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The Correct Option is B
Solution and Explanation
Step 1: Understand the reaction of carboxylic acids with sodium hydrogen carbonate.
Aryl carboxylic acids contain the functional group:
\[ -COOH \] Carboxylic acids are acidic in nature and react with sodium hydrogen carbonate \((NaHCO_3)\).
This reaction is commonly used as a test for the presence of carboxylic acid group.
Step 2: Write the general reaction.
The reaction between a carboxylic acid and sodium hydrogen carbonate is:
\[ RCOOH + NaHCO_3 \longrightarrow RCOONa + H_2O + CO_2 \] In this reaction:
\[ RCOOH \rightarrow \text{Carboxylic acid} \] \[ RCOONa \rightarrow \text{Sodium carboxylate} \] The gaseous product evolved is carbon dioxide.
Step 3: Explain the formation of gas.
Hydrogen carbonate ion reacts with the acidic proton of the carboxylic acid to form unstable carbonic acid:
\[ H_2CO_3 \] Carbonic acid immediately decomposes into:
\[ CO_2 + H_2O \] Thus, brisk effervescence is observed due to evolution of carbon dioxide gas.
Step 4: Identify the liberated gas.
Therefore, the gaseous molecule liberated is:
\[ CO_2 \]
Step 5: Match with the given options.
The correct option is:
\[ (2)\; CO_2 \]
Step 6: Final conclusion.
Hence, the gas evolved is:
\[ \boxed{CO_2} \]
Aryl carboxylic acids contain the functional group:
\[ -COOH \] Carboxylic acids are acidic in nature and react with sodium hydrogen carbonate \((NaHCO_3)\).
This reaction is commonly used as a test for the presence of carboxylic acid group.
Step 2: Write the general reaction.
The reaction between a carboxylic acid and sodium hydrogen carbonate is:
\[ RCOOH + NaHCO_3 \longrightarrow RCOONa + H_2O + CO_2 \] In this reaction:
\[ RCOOH \rightarrow \text{Carboxylic acid} \] \[ RCOONa \rightarrow \text{Sodium carboxylate} \] The gaseous product evolved is carbon dioxide.
Step 3: Explain the formation of gas.
Hydrogen carbonate ion reacts with the acidic proton of the carboxylic acid to form unstable carbonic acid:
\[ H_2CO_3 \] Carbonic acid immediately decomposes into:
\[ CO_2 + H_2O \] Thus, brisk effervescence is observed due to evolution of carbon dioxide gas.
Step 4: Identify the liberated gas.
Therefore, the gaseous molecule liberated is:
\[ CO_2 \]
Step 5: Match with the given options.
The correct option is:
\[ (2)\; CO_2 \]
Step 6: Final conclusion.
Hence, the gas evolved is:
\[ \boxed{CO_2} \]
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