Problem 22 - A Complete Resource Book in Chemistry for JEE Main

Question

The brown ring complex compound is formulated as \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{NO}\right] \mathrm{SO}_{4} .\) The oxidation state of iron in the compound is (a) 1 (b) 2 (c) 3 (d) 0

Step-by-Step Solution

Answer

The oxidation state of iron is +1 (option a).

Step 1: Identify the Known Components

The given compound is \( [\mathrm{Fe(H_2O)_5NO}]\mathrm{SO_4} \). We need to determine the oxidation state of Fe in this complex. \( \mathrm{H_2O} \) is a neutral ligand and does not contribute to the charge. \( \mathrm{SO_4}^{2-} \) has a known charge of \(-2\). The charge of NO in complexes is typically \(+1\).

Step 2: Set Up the Equation for Charge Balance

Let the oxidation state of Fe be \( x \). Considering the charges from the components, the equation for the total charge of the complex is \[x + 5(0) + 1 = 0 \]This equation results from the fact that the sum of the oxidation states for the entire complex must be zero because the complex itself is neutral.

Step 3: Solve for the Oxidation State of Iron

From the equation \[ x + 1 = 0 \], solve for \( x \). Subtract 1 from both sides to isolate \( x \):\[x = -1\]Hence, the oxidation state of iron in the compound is \(+1\).

Step 4: Confirm the Answer Matches Multiple Choice Options

The calculated oxidation state of \( +1 \) is the first option in the list provided (a) 1. Therefore, the oxidation state of iron in the given complex compound is indeed 1.

Key Concepts

Complex Compounds

Complex compounds, also known as coordination compounds, involve a central metal atom surrounded by molecules or ions known as ligands. These ligands can be anions like chloride or neutral molecules like water.
In the brown ring complex \([\mathrm{Fe(H_2O)_5NO})]\mathrm{SO_4}\), iron is the central metal atom. It is surrounded by five water molecules and one nitrosyl group (NO), forming a coordination sphere. This entire coordination sphere behaves like a single ion.

• The coordination sphere is not affected by the external ions, like \(\mathrm{SO_4}^{2-}\), which lie outside the brackets.
• Ligands within the coordination sphere determine the complex's properties, including color, magnetism, and reactivity.

Understanding these compounds is crucial in fields like medicinal chemistry where complexes are used as contrast agents and drugs.

Iron Chemistry

Iron is a highly versatile metal, playing a pivotal role not only in material science but also in biological systems. In complex compounds, iron can adopt various oxidation states, typically ranging from \(+2\) to \(+3\), but sometimes it can be other states as well.
In the brown ring complex, iron adopts an unusual oxidation state of \(+1\).

• Finding the oxidation state of iron requires considering its interaction with ligands.
• In biological systems, iron is crucial for oxygen transport and electron transfer processes.

This versatility makes iron a key component in catalysis and other industrial processes, showcasing its adaptability beyond common compounds.

Charge Balance Equation

The charge balance equation is central to understanding the net charge of complex compounds. Calculating the oxidation state involves setting up an equation considering all charges of ligands and ionized parts. For the complex compound \([\mathrm{Fe(H_2O)_5NO}])\mathrm{SO_4}\):

• The sulfate ion \(\mathrm{SO_4}^{2-}\) has a charge of \(-2\).
• The nitrosyl ligand contributes a charge, often \(+1\).
• Water restores no charge as it is neutral.

You set up the equation by representing the oxidation state of iron as \(x\), leading to the equation \[x + 5(0) + 1 = 0\]. Solving this provides \(x = -1\), highlighting the net charge of the complex as zero, ensuring electrical neutrality in coordination chemistry.