Problem 176 - A Complete Resource Book in Chemistry for JEE Main

Question

Iron exhibits \(+2\) and \(+3\) oxidation states. Which of the following statements about iron is incorrect? (a) Ferrous compounds are less volatile than the corresponding ferric compounds (b) Ferrous compounds are relatively more ionic than the corresponding ferric compounds. (c) Ferrous oxide is more basic in nature than the ferric oxide (d) Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds

Step-by-Step Solution

Answer

Statement (d) is incorrect.

Step 1: Identify Key Concepts

Identify the critical concepts related to the question: Iron can exist in two common oxidation states: +2 (ferrous) and +3 (ferric). The question involves comparing characteristics of ferrous compounds and ferric compounds.

Step 2: Analyze Each Statement

Review each statement provided in the question one by one to verify its correctness based on the chemistry of iron in its ferrous and ferric states.

Step 3: Statement (a) Analysis

Analyze the statement (a): "Ferrous compounds are less volatile than the corresponding ferric compounds." Generally, volatility is not a primary distinction between ferrous and ferric, and ferric compounds tend to be less volatile due to their higher oxidation state leading to stronger crystal lattice energy.

Step 4: Statement (b) Analysis

Analyze the statement (b): "Ferrous compounds are relatively more ionic than the corresponding ferric compounds." Ferrous compounds, being in the +2 oxidation state, are typically more ionic because the lower oxidation state usually indicates less covalent character.

Step 5: Statement (c) Analysis

Analyze the statement (c): "Ferrous oxide is more basic in nature than the ferric oxide." Ferrous oxide, being in a lower oxidation state, is generally more basic than ferric oxide, which is more acidic due to its +3 oxidation state.

Step 6: Statement (d) Analysis

Analyze the statement (d): "Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds." Hydrolysis is more prone in compounds with higher oxidation states which forms correspondingly stronger metallic-anion bonds; hence, ferrous compounds should be less easily hydrolyzed.

Step 7: Identify Incorrect Statement

Based on the analysis of each statement, statement (d) is incorrect. Ferrous compounds are not more easily hydrolysed than ferric compounds. Hydrolysis is more extensive in ferric compounds.

Key Concepts

Ferrous vs Ferric

Iron exists in two primary oxidation states, which are referred to as ferrous (Fe²⁺) and ferric (Fe³⁺). Understanding the difference is important because these states share some similarities, but they also have significant distinctions that affect their chemical properties. Ferrous compounds contain iron in the +2 oxidation state. They often exhibit a high degree of ionic character due to the lower effective nuclear charge attracting surrounding ions less strongly compared to ferric compounds. This can make ferrous compounds more reactive or soluble.
In contrast, ferric compounds involve iron in the +3 oxidation state. Iron in the ferric state has lost one more electron than in the ferrous state. This results in a higher effective nuclear charge, which enhances covalent character due to stronger attraction for nearby electrons. Ferric compounds generally show greater stability but are often less ionic in nature compared to their ferrous counterparts. This distinction is crucial when examining their behavior in different chemical reactions and environmental conditions.

Volatility of Iron Compounds

Volatility refers to a compound's tendency to vaporize. While evaluating iron compounds, it is important to note how the oxidation state can impact their volatility. Generally, volatility is less of a factor when distinguishing between ferrous and ferric compounds. However, it is often true that ferric compounds, being in a higher oxidation state, exhibit reduced volatility in comparison to ferrous compounds.
Higher oxidation states in ferric compounds lead to stronger bonding within the crystalline structure. This results in stronger lattice energies, making these compounds more stable and less likely to vaporize easily. Therefore, ferric compounds tend to have higher melting and boiling points, which is inversely related to their volatility. Understanding this principle helps to explain why ferric compounds might appear less volatile under standard laboratory conditions than their ferrous counterparts.

Basicity of Oxides

The basicity of an oxide can be linked with the oxidation state of the metal involved. Oxides can be categorized as more acidic, basic, or amphoteric, depending in part on the oxidation state of the metal.
For iron oxides, ferrous oxide (9O) is generally more basic than ferric oxide (9O₃), due to the lower oxidation state of iron in the ferrous form. The lower oxidation state implies a lesser ability to attract proton donors, making it relatively more basic. In contrast, ferric oxide, with iron in the +3 oxidation state, tends to be more acidic due to the higher effective nuclear charge, which can attract and stabilize electrons more effectively.

• Ferrous oxide (9O) is basic because of the lower charge density on 9.
• Ferric oxide (9O₃) is more acidic, influenced by a higher oxidation state which stabilizes electrons.

This concept helps to understand the reactivity and solubility of these oxides in water and their behavior towards acids and bases.

Hydrolysis of Compounds

Hydrolysis is the process where a compound reacts with water, resulting in the breakdown of that compound. In the context of iron compounds, hydrolysis behavior varies depending on the oxidation state of the iron. Typically, compounds with higher oxidation states are more susceptible to hydrolysis because increased charge density results in more polar and reactive bonds.
Ferric compounds, containing Fe³⁺, are more likely to undergo hydrolysis than ferrous compounds, as the higher positive charge attracts water molecules more strongly, facilitating the hydrolysis process. This leads to the formation of more developed and smaller species such as hydroxides that are often precipitated from solution. - Ferric compounds are more readily hydrolyzed due to strong interaction with water. - Ferrous compounds, with lower oxidation states, are less prone to hydrolysis. Understanding this difference is essential for predicting the stability of iron compounds in aqueous solutions and their behavior in environmental processes.