Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

A and B react with Na gives \(\mathrm{H}_{2}\) gas and by reaction of both \(\mathrm{A}\) and \(\mathrm{B}\) ethyl acetate is formed then \(\mathrm{A}\) and \(\mathrm{B}\) are (a) \(\mathrm{CH}_{3} \mathrm{COOH}, \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (b) \(\mathrm{CH}_{3} \mathrm{COOH}, \mathrm{CH}_{3} \mathrm{OH}\) (c) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{COOH}, \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\) (d) \(\mathrm{HCOOH}, \mathrm{CH}_{3} \mathrm{COOH}\)

Step-by-Step Solution

Answer

(a) \( \text{CH}_3\text{COOH}, \text{C}_2\text{H}_5\text{OH} \).

Step 1: Understand the Reaction with Na

Both substances \( A \) and \( B \) react with sodium (Na) to produce \( \text{H}_2 \) gas. Typically, carboxylic acids and alcohols react with \( \text{Na} \) to evolve hydrogen gas. Our options include combinations of these compounds.

Step 2: Consider Formation of Ethyl Acetate

Ethyl acetate (\( \text{CH}_3\text{COOC}_2\text{H}_5 \)) is formed through a reaction known as esterification, where an alcohol reacts with a carboxylic acid. This gives us a clue that substance \( A \) must be \( \text{CH}_3\text{COOH} \) (acetic acid) and substance \( B \) must be \( \text{C}_2\text{H}_5\text{OH} \) (ethanol).

Step 3: Match Options with Reaction Clues

Among the given options, only the pair (a) \( \text{CH}_3\text{COOH} \) and \( \text{C}_2\text{H}_5\text{OH} \) can react together in the presence of a catalyst to form ethyl acetate through esterification. Additionally, each reacts with Na to produce hydrogen gas.

Step 4: Conclusion

Based on the reactions provided, \( A \) is acetic acid (\( \text{CH}_3\text{COOH} \)) and \( B \) is ethanol (\( \text{C}_2\text{H}_5\text{OH} \)). The correct pair for \( A \) and \( B \) in the context of the problem is option (a).

Key Concepts

Ethyl Acetate

To understand ethyl acetate, let's delve into what it is and how it's formed. Ethyl acetate is a colorless liquid with a sweet and fruity smell, and it belongs to a class of compounds known as esters. It is widely used in industries as a solvent and is a component of nail polish removers and glues.⠀
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• It is formed through a reaction known as esterification.
• Esterification is a process where a carboxylic acid reacts with an alcohol, typically with an acid catalyst, to form an ester and water.

⠀For ethyl acetate specifically, the reaction involves acetic acid (ch\( \text{CH}_3\text{COOH} \)) and ethanol (ch\( \text{C}_2\text{H}_5\text{OH} \)).ch The balanced equation for this reaction is:\[\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \rightarrow\u000a \text{CH}_3\text{COOC}_2\text{H}_5 \u000a+ \text{H}_2\text{O}\]This reaction is typically facilitated by the presence of an acid catalyst like sulfuric acid, which speeds up the process without being consumed. Esters like ethyl acetate are known for their pleasant fragrances, making them valuable in perfumes and flavorings.

Sodium Reaction

When certain compounds such as alcohols and carboxylic acids react with sodium (Na), a fascinating chemical process takes place. Upon this reaction, hydrogen gas is evolved, and the sodium takes the place of hydrogen atoms in these compounds, forming sodium salts.

Why does this occur? Let's break it down:

• Alcohols, like ethanol, participate in this reaction by ionizing to form sodium ethoxide and hydrogen gas. For example, with ethanol, the reaction is:\[\text{2 C}_2\text{H}_5\text{OH} + 2\text{Na} \rightarrow 2\text{C}_2\text{H}_5\text{ONa} + \text{H}_2\]
• For acetic acid, a similar process occurs, forming sodium acetate:\[\text{2 CH}_3\text{COOH} + 2\text{Na} \rightarrow \text{2 CH}_3\text{COONa} + \text{H}_2\]

This kind of reaction is a hallmark of active metals with protic solvents, which contain hydrogen atoms that can be released as hydrogen gas. Hydrogen is displaced from the original compound and appears as a gas, a sign of the chemical change.

Hydrogen Gas

Hydrogen gas (\( \text{H}_2 \)) is the simplest and lightest element in the universe. Often, when learning chemistry, it's important to understand how this gas is produced in reactions and its implications.⠀

Hydrogen has the following notable characteristics:

• It is colorless, odorless, and tasteless.
• Hydrogen is flammable, so it can combust to release energy, making it a potential clean fuel.
• In chemical reactions, hydrogen can act both as a reducing agent and is often evolved as a gas when reactive metals come in contact with water or acids.

In the context of our exercise, when alcohols and acid react with sodium (Na), the hydrogen component of these molecules is released as hydrogen gas:\[\text{2C}_2\text{H}_5\text{OH} + 2\text{Na} \rightarrow 2\text{C}_2\text{H}_5\text{ONa} + \text{H}_2 \]This gas evolution not only tells us about the chemical changes occurring but also plays a key role in identifying the substances (ch\( \text{A} \) and \( \text{B} \)) in certain chemical reaction problems. Understanding hydrogen's involvement in these reactions helps us better comprehend the nature of chemical processes.