Problem 102 - A Complete Resource Book in Chemistry for JEE Main

Question

When washing soda is heated (a) \(\mathrm{CO}_{2}\) is released (b) water vapour is released (c) \(\mathrm{CO}_{2}\) is released (d) \(\mathrm{CO}+\mathrm{CO}_{2}\) is released

Step-by-Step Solution

Answer

Water vapor is released.

Step 1: Identify the Compound

Washing soda is chemically known as sodium carbonate decahydrate and is represented by the formula \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \). This compound contains water molecules in its crystalline structure.

Step 2: Understand the Heating Process

When washing soda is heated, it loses its water of crystallization. This means the water molecules are released as water vapor. The reaction can be depicted as: \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \rightarrow \text{Na}_2\text{CO}_3 + 10\text{H}_2\text{O}\uparrow \), showing the release of water vapor.

Step 3: Evaluate Gas Release Possibilities

Sodium carbonate, \( \text{Na}_2\text{CO}_3 \), is stable and does not decompose to release \( \text{CO}_2 \) or \( \text{CO} \) upon simple heating. Hence, there is no release of \( \text{CO}_2 \) or \( \text{CO} \) when washing soda is heated. This confirms that only water vapor is released.

Key Concepts

Sodium Carbonate Decahydrate

Sodium carbonate decahydrate is commonly known as washing soda. It is an essential compound used in various cleaning applications due to its strong alkaline properties. This compound is defined by its chemical formula \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \). The formula indicates that each molecule of sodium carbonate decahydrate is associated with 10 molecules of water. These water molecules are integral to the crystalline structure of the compound. This characteristic crystalline nature makes sodium carbonate decahydrate efficient at absorbing moisture from the environments it is used in. Understanding this structure is crucial as it forms the basis for how the compound behaves when it undergoes different processes, such as heating.

Water of Crystallization

Water of crystallization refers to the water molecules that are part of the crystalline framework of a compound. In the case of washing soda, the water of crystallization is represented by the 10 molecules of water in its chemical formula \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \). These water molecules can be removed through heating. When washing soda is heated, the crystal structure breaks down and water molecules are released as water vapour.
This process is known as dehydration. Importantly, the loss of water of crystallization doesn't alter the chemical nature of the remaining sodium carbonate. It simply shifts from a hydrated to an anhydrous form, \( \text{Na}_2\text{CO}_3 \), which means without water. This is why heating washing soda results in water vapor without changing the nature of the sodium carbonate itself.

Gas Release in Chemical Reactions

Understanding the gas release in chemical reactions is fundamental in chemistry. When heating washing soda, only water vapour is released. This happens because the action involves losing water of crystallization.
However, it's important to note the stability of sodium carbonate in this reaction. Unlike some other chemical compounds, sodium carbonate doesn't break down further to release \( \text{CO}_2 \) or any other gases when it is heated.
Knowing this stability helps in predicting and understanding other reactions involving sodium carbonate. In many industrial and laboratory processes, this property is beneficial, as the compound can retain its functionality without decomposing into other components unless specific conditions induce such changes. This makes sodium carbonate a useful component in controlled chemical applications where precise reactions are essential.