Problem 22 - A Complete Resource Book in Chemistry for JEE Main

Question

Sodium is heated in air at \(300^{\circ} \mathrm{C}\) to form X.X absorbs \(\mathrm{CO}_{2}\) and forms \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{Y}\). Which of the following is Y? (a) \(\mathrm{O}_{2}\) (b) \(\mathrm{O}_{3}\) (c) \(\mathrm{H}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{O}_{2}\)

Step-by-Step Solution

Answer

Compound Y is \( \mathrm{O}_2 \).

Step 1: Determine the Compound X

When sodium (Na) is heated in air, it reacts with oxygen to form sodium oxide, which is \( \mathrm{Na}_2 \mathrm{O} \). Thus, compound X is \( \mathrm{Na}_2 \mathrm{O} \).

Step 2: Reaction of X with CO2

Sodium oxide (X) reacts with carbon dioxide (\( \mathrm{CO}_2 \)) to form sodium carbonate (\( \mathrm{Na}_2 \mathrm{CO}_3 \)) and another compound Y. The reaction can be given by: \( \mathrm{Na}_2 \mathrm{O} + \mathrm{CO}_2 \rightarrow \mathrm{Na}_2 \mathrm{CO}_3 + \mathrm{Y} \).

Step 3: Identify Compound Y

To balance the reaction \( \mathrm{Na}_2 \mathrm{O} + \mathrm{CO}_2 \rightarrow \mathrm{Na}_2 \mathrm{CO}_3 + \mathrm{Y} \), notice that sodium carbonate \( \mathrm{Na}_2 \mathrm{CO}_3 \) is formed without additional oxygen or hydrogen atoms, indicating that no extra O atoms are needed. Therefore, Y must be \( \mathrm{O}_2 \).

Key Concepts

Formation of sodium oxide

Sodium oxide, chemically represented as \( \text{Na}_2\text{O} \), is created when sodium (\( \text{Na} \)) is heated in the presence of oxygen at a high temperature, such as \(300^{\circ} \text{C}\). This process is an example of a synthesis reaction where two substances combine to form a new compound.
The equation for this chemical reaction is:

• 4\( \text{Na} \) + \( \text{O}_2 \) \( \rightarrow \) 2\( \text{Na}_2\text{O} \)

In this reaction, four sodium atoms react with one molecule of oxygen to yield two molecules of sodium oxide.
This demonstrates sodium's high reactivity, especially with non-metals like oxygen, and highlights the formation of a basic oxide.

Sodium reaction with carbon dioxide

When sodium oxide (\( \text{Na}_2\text{O} \)) comes into contact with carbon dioxide (\( \text{CO}_2 \)), it reacts to form sodium carbonate (\( \text{Na}_2\text{CO}_3 \)). This is an example of a basic oxide reacting with an acidic oxide to form a salt, demonstrating an acid-base reaction.
The chemical equation for this reaction is:

• \( \text{Na}_2\text{O} + \text{CO}_2 \rightarrow \text{Na}_2\text{CO}_3 \)

Through this process, sodium oxide acts as a base that neutralizes the acidic carbon dioxide to form the salt sodium carbonate.
Additionally, one of the products, and the compound referred to as "Y" in the problem, is oxygen (\( \text{O}_2 \)), indicating that the oxygen atom in \( \text{Na}_2\text{O} \) is effectively being transferred into the \( \text{CO}_2 \), thus creating \( \text{Na}_2\text{CO}_3 \) while liberating molecular oxygen.

Balancing chemical equations

Balancing chemical equations is crucial for accurately representing the conservation of mass in a chemical reaction. This concept ensures the same number of each type of atom appears on both sides of an equation.
To balance the equation \( \text{Na}_2\text{O} + \text{CO}_2 \rightarrow \text{Na}_2\text{CO}_3 + \text{Y} \), we observe the following:

• Sodium (\( \text{Na} \)) atoms: There are already two on each side.
• Carbon (\( \text{C} \)) atoms: Present in one molecule of \( \text{CO}_2 \) and transferred fully into \( \text{Na}_2\text{CO}_3 \).
• Oxygen (\( \text{O} \)) atoms: Start with three in total (from \( \text{Na}_2\text{O} \) and \( \text{CO}_2 \)) and must balance to three on the product side, thus \( \text{Y} \) is \( \text{O}_2 \).

Through these observations, we confirm \( \text{Y} = \text{O}_2 \) balances the chemical equation. This demonstrates that even though not all species change, a balanced equation respects the principle that mass and atoms are neither created nor destroyed in the reaction process.