Problem 99 - A Complete Resource Book in Chemistry for JEE Main

Question

Ferrous ion change to \(X\) ion, on reacting with acidified hydrogen peroxide. The number of d-electrons present in \(\mathrm{X}\) and its magnetic moment (in BM) are respectively (a) 5 and \(4.9\) (b) 4 and \(5.92\) (c) 6 and \(6.95\) (d) 5 and \(5.92\)

Step-by-Step Solution

Answer

The number of d-electrons is 5, and the magnetic moment is 5.92 BM, matching option (d).

Step 1: Determine the Initial Electron Configuration of Fe

The atomic number of Fe is 26. Therefore, its electron configuration is [Ar] 3d\(^6\) 4s\(^2\). The d-electrons are the ones in the 3d subshell, meaning there are initially 6 d-electrons.

Step 2: Determine the Electron Configuration of Fe\(^{2+}\)

When iron loses two electrons to form Fe\(^{2+}\), these electrons are removed from the 4s and 3d subshells. Thus, Fe\(^{2+}\) has the electron configuration [Ar] 3d\(^6\), containing 6 d-electrons.

Step 3: Determine the Change in Oxidation State

In the presence of acidified hydrogen peroxide, Fe\(^{2+}\) is further oxidized to Fe\(^{3+}\). Thus, loses one more electron from the 3d subshell.

Step 4: Write the Electron Configuration of Fe\(^{3+}\)

With Fe\(^{2+}\) oxidized to Fe\(^{3+}\), Fe\(^{3+}\)'s electron configuration becomes [Ar] 3d\(^5\). Therefore, the number of d-electrons in X is 5.

Step 5: Calculate Magnetic Moment

The magnetic moment \(\mu\) in Bohr Magnetons (BM) is calculated using the formula \(\mu = \sqrt{n(n+2)}\), where \(n\) is the number of unpaired electrons. Since Fe\(^{3+}\) has 5 unpaired d-electrons, \(\mu = \sqrt{5(5+2)} = \sqrt{35} = 5.92\) BM.

Key Concepts

Ferrous Ion

The term "ferrous ion" refers to the iron ion in the +2 oxidation state, commonly denoted as Fe\(^{2+}\). Iron, a transition metal, often exists in multiple oxidation states, with Fe\(^{2+}\) being one of the most stable and common forms. This ion is formed when elemental iron loses two electrons, specifically from its outermost 4s subshell. This results in the electron configuration [Ar] 3d\(^6\), showing the presence of six electrons in the 3d subshell.

• Ferrous ions are prominent in various biochemical and industrial processes.
• They can be further oxidized to higher oxidation states under specific conditions, such as the presence of oxidizing agents.

The role of ferrous ions in biological systems is also vital, where they participate in electron transfer reactions and are components of many important enzymes.

Oxidation State

The oxidation state indicates the degree of oxidation or loss of electrons an element exhibits in a particular chemical compound. Specifically for iron, the oxidation state can vary, but common states include Fe\(^{2+}\) and Fe\(^{3+}\). An element's oxidation state is determined by theoretical ionic charges assigned to atoms, reflecting electron transfer.

• For Fe\(^{2+}\), the iron atom has lost two electrons, leading to its +2 oxidation state.
• Upon reaction with oxidizing agents like acidified hydrogen peroxide, Fe\(^{2+}\) becomes Fe\(^{3+}\) by losing an additional electron, modifying its electron configuration to [Ar] 3d\(^5\).

Understanding the oxidation state helps predict the behavior of an element in reactions, including changes in magnetic properties and interactions with ligands or other chemical species.

Magnetic Moment

The magnetic moment is a crucial property that quantifies the magnetic strength and orientation of a system, especially a magnetic material like transition metal ions. For transition metal ions, the magnetic moment arises from unpaired electrons in the d-orbitals. It's calculated using the formula \(\mu = \sqrt{n(n+2)}\) where \(n\) is the number of unpaired electrons.

• For Fe\(^{3+}\), the electron configuration is [Ar] 3d\(^5\), indicating five unpaired electrons.
• Substitute \(n = 5\) into the formula to find \(\mu = \sqrt{5(5+2)} = 5.92\) Bohr Magnetons (BM).

The value of the magnetic moment provides insights into the number of unpaired electrons, assisting in identifying the oxidation state and elemental behavior across different conditions.

Transition Metals

Transition metals are found in the central block of the periodic table, characterized by their ability to form compounds with variable oxidation states, as opposed to more defined states found in other element categories. These metals, including iron, have partially filled d-orbitals which give rise to their unique properties.

• Significant transition metals include iron (Fe), copper (Cu), nickel (Ni), and others.
• They play vital roles in catalysis, metallurgy, and biological systems due to their diverse oxidation states and coordination compounds.

The chemistry of transition metals is primarily defined by their electron configurations. As these elements have various stable d-electron configurations, they can display distinct oxidation states and magnetic moments, depending on the chemical environment.