Iron exhibit + 2 and + 3 oxidation states. Which of the following statements about iron is incorrect?

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Engineering

Chemistry

Fajans Rule and Its Application

d Block Elements and Properties

Periodic Trend of Properties of d Block Elements

Question

Iron exhibit + 2 and + 3 oxidation states. Which of the following statements about iron is incorrect?

A

Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds.

B

Ferrous oxide is more basic in nature than the ferric oxide.

C

Ferrous compounds are less volatile than the corresponding ferric compounds.

D

Ferrous compounds are relatively more ionic than the corresponding ferric compounds.

Iron exhibits +2 (ferrous) and +3 (ferric) oxidation states. The key concept is that a higher positive charge on a cation leads to a smaller ionic radius and higher charge density. This makes Fe³⁺ a smaller, more polarizing ion than Fe²⁺. Therefore, ferric (Fe³⁺) compounds are generally more covalent, more easily hydrolyzed, and less volatile and ionic than their ferrous (Fe²⁺) counterparts. Ferric oxide ( ${Fe}_{2} O_{3}$ ) is also less basic than ferrous oxide ( $FeO$ ).

Final Answer: The incorrect statement is "Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds."

Iron exhibits two common oxidation states: +2 (ferrous) and +3 (ferric). The incorrect statement among the options is: Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds.

Detailed Explanation:

Let's analyze each statement step by step:

Step 1: Hydrolysis Tendency
Hydrolysis in ionic compounds is influenced by the charge density of the cation. Higher charge density leads to greater polarization of water molecules, facilitating hydrolysis. The charge density of Fe³⁺ is higher than that of Fe²⁺ due to its smaller ionic size and higher charge. Therefore, ferric compounds hydrolyze more easily than ferrous compounds. The first statement is incorrect.

Step 2: Basic Nature of Oxides
Basic character of oxides decreases with increasing oxidation state. FeO (ferrous oxide) is basic, while Fe₂O₃ (ferric oxide) is amphoteric. Thus, ferrous oxide is more basic than ferric oxide. This statement is correct.

Step 3: Volatility
Volatility is related to the covalent character of compounds. Ferric compounds, due to higher charge on Fe³⁺, have more covalent character (Fajans' rule) and are more volatile. Ferrous compounds are less volatile. This statement is correct.

Step 4: Ionic Character
According to Fajans' rules, smaller cation size and higher charge increase covalent character. Fe³⁺ has higher charge and smaller size compared to Fe²⁺, so ferric compounds are more covalent. Ferrous compounds are more ionic. This statement is correct.

Related Topics & Formulae:

Fajans' Rules: Covalent character in ionic compounds increases with:
1. Smaller cation size
2. Larger anion size
3. Higher charge on ions

Hydrolysis Reaction Example:
${Fe}^{3 +} + 3 H_{2} O \to Fe (OH) 3_{(s)} + 3 H^{+}$

Key Theory: The higher the oxidation state, the greater the polarizing power of the cation, leading to increased covalent character, volatility, and hydrolysis tendency.