Problem 5 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is formed when ferrous oxalate is heated in the absence of air? (a) \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{Fe}_{3} \mathrm{O}_{4}\) (c) \(\mathrm{Fe}_{2} \mathrm{O}_{4}\) (d) \(\mathrm{FeO}\)

Step-by-Step Solution

Answer

(d) \(\mathrm{FeO}\)

Step 1: Understanding Ferrous Oxalate

Ferrous oxalate, known chemically as FeC2O4, is a compound containing iron in a +2 oxidation state and oxalate ions (C2O4)^2-. When heated in the absence of air, it decomposes. It is important to know the chemical reaction that describes this process.

Step 2: Understanding Decomposition Reaction

When ferrous oxalate is heated, it decomposes to form iron (II) oxide (FeO) and carbon dioxide (CO2). The reaction is: \( \mathrm{FeC}_{2}\mathrm{O}_{4} \rightarrow \mathrm{FeO} + \mathrm{CO}_{2} + \mathrm{CO} \)

Step 3: Analyze Formation of Products

The decomposition reaction shows the formation of iron (II) oxide (FeO) as the solid product present after heating. The gases, CO2 and CO, escape, leaving FeO behind.

Step 4: Select the Correct Answer Choice

The compound formed upon heating ferrous oxalate is iron (II) oxide (FeO). Given the options: (a) \(\mathrm{Fe}_{2}\mathrm{O}_{3}\) (b) \(\mathrm{Fe}_{3}\mathrm{O}_{4}\) (c) \(\mathrm{Fe}_{2}\mathrm{O}_{4}\) (d) \(\mathrm{FeO}\), the correct answer is (d) \(\mathrm{FeO}\).

Key Concepts

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into different substances. In the case of ferrous oxalate, when heated, it undergoes a chemical reaction known as decomposition. This transformation results in the breakdown of ferrous oxalate into simpler components.
During this reaction, ferrous oxalate is converted into iron (II) oxide and gases, specifically carbon dioxide (CO₂) and carbon monoxide (CO). Here's the chemical equation showcasing this change:
\[ ext{FeC}_{2} ext{O}_{4} ightarrow ext{FeO} + ext{CO}_{2} + ext{CO} \]
Through this equation, we can observe the roles each molecule plays.

• The molecule FeC₂O₄ is the reactant, the starting substance.
• FeO, CO₂, and CO are the products, indicating what forms after the reaction.

Understanding this basic concept of chemical reactions helps in comprehending how ferrous oxalate transforms during thermal decomposition.

Iron (II) Oxide Formation

Iron (II) oxide, commonly referred to as FeO, is the main product formed when ferrous oxalate decomposes. This particular reaction occurs under conditions without air.
When ferrous oxalate is subjected to heat, it breaks down, and one of the substances that emerges is this iron-based compound. Iron (II) oxide is a black powdery substance characterized by iron in the +2 oxidation state.
It's crucial to grasp that during this transformation, the removal of oxalate ions leads to the formation of both FeO and gaseous byproducts, CO₂ and CO.
Being aware of FeO’s properties, particularly its formation through decomposition, is vital for understanding the entire process.

Oxidation States

Understanding oxidation states, or oxidation numbers, is key in the study of chemical reactions. These numbers depict the degree of oxidation of an atom within a compound. In ferrous oxalate, iron originally exists in the +2 oxidation state, indicating it has lost two electrons relative to its elemental state.
During the decomposition of FeC₂O₄, iron retains this +2 oxidation state when it forms FeO. Therefore, this transformation is considered straightforward in terms of oxidation states, as the iron does not undergo any change in this respect.
In contrast, the other elements in the reaction, primarily the oxalate, undergo changes in oxidation states when breaking down into CO₂ and CO gases.
Understanding the stability of iron in its +2 state during this particular reaction can be insightful for students studying redox processes.

Thermal Decomposition

Thermal decomposition is a type of chemical reaction where heat breaks down a complex substance into simpler substances. Ferrous oxalate's decomposition is a prime example of this process.
When ferrous oxalate is heated without the presence of air, it undergoes thermal decomposition. The heat energy acts as a catalyst, breaking the bonds within the oxalate ions and leading to the creation of iron (II) oxide and gases such as carbon dioxide and carbon monoxide.
In this specific context, the reaction is unassisted by oxygen, differentiating it from oxidative processes.

• This ensures that any oxidation change comes internally, within the structure of ferrous oxalate itself.
• The absence of external reactants like O₂ is critical, as this would otherwise influence the substances formed.

Understanding thermal decomposition will enhance comprehension of how heat influences chemical bonds and the structure of materials, leading learners to appreciate the concept of decomposition reactions without external reactants.