Problem 48 - A Complete Resource Book in Chemistry for JEE Main

Question

When benzene sulphonic acid and p-nitrophenol are treated with \(\mathrm{NaHCO}_{3}\), the gases released respectively are: (a) \(\mathrm{SO}_{2}, \mathrm{NO}_{2}\) (b) \(\mathrm{SO}_{2}, \mathrm{NO}\) (c) \(\mathrm{SO}_{2}, \mathrm{CO}_{2}^{2}\) (d) \(\mathrm{CO}_{2}^{2}, \mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

(d) CO2, CO2

Step 1: Understanding the Compounds

First, let's understand the structure of the given compounds: benzene sulphonic acid is an aromatic sulfonyl compound ( ext{R-SO}_{3} ext{H}) and p-nitrophenol has both a hydroxy group ( ext{OH}) and a nitro group ( ext{NO}_{2}) attached to a benzene ring.

Step 2: Reactions with Sodium Bicarbonate

Next, examine how each of these compounds react with  ext{NaHCO}_3. Sodium bicarbonate reacts with acids to release carbon dioxide ( ext{CO}_{2}). Benzene sulphonic acid, being acidic due to the  ext{SO}_{3} ext{H} group, will react by releasing  ext{CO}_{2}. p-nitrophenol is acidic as well, although less acidic, and will also release  ext{CO}_{2} when reacted.

Step 3: Gases Released

Determine the gases released from the reactions with  ext{NaHCO}_3: Both benzene sulphonic acid and p-nitrophenol release  ext{CO}_{2} gas upon reaction with  ext{NaHCO}_3 due to the acidic nature of the hydrogen linked to functional groups that react to produce carbon dioxide gas.

Step 4: Matching with Options

Compare the conclusions from the chemical reactions with the given options. Since both reactions mainly lead to the release of  ext{CO}_{2}, option (d), " ext{CO}_{2}, ext{CO}_{2}," correctly represents the gases released.

Key Concepts

Benzene Sulphonic Acid

Benzene sulphonic acid is a key compound in various chemical processes. It is formed when benzene, a simple aromatic compound, is treated with sulfuric acid under certain conditions. This transformation introduces a sulfonyl functional group, represented as \(\text{SO}_3\text{H}\), into the benzene ring.
The sulfonyl group is highly electronegative, which makes benzene sulphonic acid quite acidic. In reactions, it readily donates a hydrogen ion (\(\text{H}^+\)).

• This acid's reactivity is pivotal in electrophilic aromatic substitution reactions.
• It also finds application in the production of detergents, dyes, and even medications.

When benzene sulphonic acid reacts with sodium bicarbonate \((\text{NaHCO}_3)\), it releases carbon dioxide \((\text{CO}_2)\) as a product of the neutralization reaction. This is because the sulfonic acid donates a proton to the bicarbonate ion, forming water and carbon dioxide gas. This reaction highlights the acidic nature of benzene sulphonic acid.

p-Nitrophenol

p-Nitrophenol is a common organic compound known for having a phenolic structure with a nitro group \((\text{NO}_2)\) attached at the para position (opposite to the hydroxyl \((\text{OH})\) group). This compound is characterized by its yellow color and is often utilized as a pH indicator or in the manufacture of various other chemical products.
The phenolic \((\text{OH})\) group in p-nitrophenol is acidic, allowing it to engage in reactions typical of weak acids. This stems from the ability of the \(\text{OH}\) group to donate a hydrogen ion \((\text{H}^+)\). However, the presence of the nitro group, which is an electron-withdrawing group, further enhances this acidity by stabilizing the negative charge on the oxygen after it loses the hydrogen ion.
When p-nitrophenol reacts with \(\text{NaHCO}_3\), carbon dioxide \((\text{CO}_2)\) is released, similar to benzene sulphonic acid. The bicarbonate ion reacts with the acidic hydrogen on the \(\text{OH}\) group, producing carbon dioxide. This demonstrates the compound's weakly acidic nature and emphasizes its ability to react in acid-base interactions.

Sodium Bicarbonate Reaction

Sodium bicarbonate, commonly known as baking soda, is a versatile chemical compound with the formula \(\text{NaHCO}_3\). It serves as a mild base and is widely used to neutralize acids across various fields, from baking to chemistry.
The key to sodium bicarbonate's reactivity lies in its ability to undergo acid-base reactions, where it works by neutralizing acids to produce a salt, water, and carbon dioxide gas. This is represented by the general reaction:

• \(\text{Acid} + \text{NaHCO}_3 \rightarrow \text{Salt} + \text{H}_2\text{O} + \text{CO}_2\)

In the context of benzene sulphonic acid and p-nitrophenol, both compounds are acidic enough to react with sodium bicarbonate to yield carbon dioxide. This release of \(\text{CO}_2\) is characterized by effervescence or bubbling, a physical sign of the reaction.
This type of reaction is not only important for understanding acid-base interactions but also provides practical insight into how substances like sodium bicarbonate can neutralize and influence the behavior of acidic compounds in a variety of chemical processes.