Problem 19 - A Complete Resource Book in Chemistry for JEE Main

Question

Ferrous ion changes to X ion, on reacting with acidified hydrogen peroxide. The number of d-electrons present in \(\mathrm{X}\) and its magnetic moment (in B.M.) 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 in \(\mathrm{X}\) is 5, and its magnetic moment is 5.92 B.M.

Step 1: Identify the Initial and Final States

The ferrous ion is denoted as \(\mathrm{Fe^{2+}}\), meaning it has 2 electrons removed from its neutral state. The ion \(\mathrm{X}\) represents the final state after the reaction.

Step 2: Determine the Resulting Ion

In reacting with acidified hydrogen peroxide, \(\mathrm{Fe^{2+}}\) is often oxidized to ferrous ion \(\mathrm{Fe^{3+}}\). This is because hydrogen peroxide is an oxidizing agent.

Step 3: Count the d-Electrons in \(\mathrm{Fe^{3+}}\)

The electron configuration of iron is \([\mathrm{Ar}] 3d^6 4s^2\). For \(\mathrm{Fe^{2+}}\), it has lost 2 electrons and becomes \([\mathrm{Ar}] 3d^6\). When oxidized to \(\mathrm{Fe^{3+}}\), it loses another electron, resulting in \([\mathrm{Ar}] 3d^5\). Thus, \(\mathrm{Fe^{3+}}\) has 5 d-electrons.

Step 4: Calculate the Magnetic Moment

The formula for the magnetic moment is \(\mu = \sqrt{n(n+2)}\) B.M., where \(n\) is the number of unpaired electrons.\(\mathrm{Fe^{3+}}\) has 5 unpaired electrons, so \(\mu = \sqrt{5(5+2)} = \sqrt{35} \approx 5.92\) B.M.

Key Concepts

Transition Metals Overview

Transition metals are elements found in the d-block of the periodic table. They include elements like iron, copper, and nickel. One of their defining characteristics is their ability to form ions with different oxidation states. This is due to their unique electron configuration, where their d-subshells are partially filled.

A key feature of transition metals is their colorful compounds. These colors arise from electron transitions between different d-orbitals, prompted by light absorption. Additionally, transition metals are often good catalysts. This is because they can lend or borrow electrons from reactants, facilitating chemical reactions.

• They have high melting and boiling points.
• They exhibit magnetic properties.
• They can form complex ions with multiple ligands.

Electron Configuration Explained

Electron configuration is a description of how electrons are distributed in an atom’s orbitals. It follows a specific order based on the increasing energy levels. This order is commonly known as the Aufbau principle.

The electron configuration generally follows the pattern of filling from lower to higher energy levels, starting with the 1s orbital. For transition metals, the d-orbital plays a significant role. When writing the configuration of iron (4; 26 protons and 30 electrons in its neutral state), it reads as 1]3d^{6} 4s^{2}].

With ionization, electrons are typically removed from the outermost shell first. For example, in 1], losing two electrons forms 1] 3d^{6}]. Upon further ionization to 1], an additional electron is removed, resulting in 1] 3d^{5}].

• Electrons fill the lowest energy orbitals first.
• d-electrons in transition metals affect their chemical behavior.
• Pauli's Exclusion Principle states no two electrons in an atom can have the same set of four quantum numbers.

Role of Oxidizing Agents

Oxidizing agents are substances that gain electrons during a chemical reaction, causing another substance to be oxidized. Think of them as electron acceptors. In redox reactions, oxidizing agents play a pivotal role.

Hydrogen peroxide (1]) exemplifies a common oxidizing agent. It's capable of taking an electron from 1], transforming it to 1]. This occurs because oxidizing agents are typically very electronegative, meaning they have a strong pull on electrons.

The presence of oxidizing agents is crucial for redox reactions. Such reactions are central to many chemical processes, including combustion, respiration, and cellular metabolism.

• Reduces its own oxidation state by gaining electrons.
• Often contains oxygen or halogen molecules.
• Essential for various energy production processes in organisms.