Problem 17 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

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 is : [1987-1 Mark] (a) 1 (b) 2 (c) 3 (d) 0

Step-by-Step Solution

Answer

The oxidation state of iron is 2.

Step 1: Identify Ligands and Charge Contribution

First, identify the ligands present in the complex. The given compound is \( [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_5(\mathrm{NO})] \mathrm{SO}_4 \), which includes water (\(\mathrm{H}_2\mathrm{O}\)) and nitric oxide (\(\mathrm{NO}\)) as ligands. Water (\(\mathrm{H}_2\mathrm{O}\)) is a neutral ligand, contributing a net charge of zero. Nitric oxide (\(\mathrm{NO}\)) is also considered a neutral ligand in this context, contributing zero charge.

Step 2: Analyze the Balance of Charges

Now, consider the overall charge of the complex. The sulfate ion (\(\mathrm{SO}_4^{2-}\)) indicates a charge balance because it typically carries a 2- charge. The entire complex must also balance this charge, implying the rest of the compound \([\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_5(\mathrm{NO})]\) should have an overall charge of 2+ to balance the sulfate ion's 2-.

Step 3: Determine the Oxidation State of Iron

To find the oxidation state of iron (\(\mathrm{Fe}\)), assume it is \(x\). Since the ligands contribute zero charge, the iron must contribute enough charge to make the complex \([\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_5(\mathrm{NO})]\) yield an overall 2+ charge. Hence we have: \[ x + 0 = +2 \] Thus, the oxidation state of \(\mathrm{Fe}\) is \(+2\).

Key Concepts

Understanding Complex Compounds

Complex compounds, also known as coordination compounds, are fascinating entities in chemistry. They consist of a central metal atom or ion bonded to a set of surrounding molecules or ions, known as ligands. These compounds exhibit diverse structures and properties. The central metal, like iron in our exercise, coordinates with ligands to form a complex. This central atom's role in the chemical behavior of the compound is crucial.

In the brown ring complex compound \([\mathrm{Fe}(\mathrm{H}_{2}\mathrm{O})_{5}(\mathrm{NO})] \mathrm{SO}_{4}\), iron acts as the central metal. This iron atom strongly interacts with water and nitric oxide molecules. These ligands surround and stabilize the iron, forming a robust and distinct molecular structure.

Role of Ligands in Coordination Chemistry

Ligands are vital components in coordination chemistry. They are molecules or ions that donate at least one pair of electrons to a central atom or ion to form a coordination bond. This interaction between ligands and the central metal atom significantly impacts the properties and stability of the complex compound. The nature of the ligands affects many facets like color, reactivity, and magnetic properties.

In the context of our brown ring complex, we have water (\(\mathrm{H}_2\mathrm{O}\)) and nitric oxide (\(\mathrm{NO}\)) acting as ligands. Both these ligands are neutral, meaning they do not change the charge of the complex directly. However, they play a crucial role in stabilizing the structure by surrounding the iron ion through coordination bonds. Understanding that these ligands provide stability but do not affect the charge simplifies determining the oxidation states of the complex's components.

Charge Balancing in Coordination Compounds

Charge balancing is a key concept in the chemistry of complex compounds. The charges of all components within a coordination compound must sum to zero or reflect the charge of the compound if it’s an ion. In our example, \([\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_5(\mathrm{NO})] \mathrm{SO}_4 \), proper charge balancing is essential to determining the oxidation state of iron (\(\mathrm{Fe}\)).

Sulfate (\(\mathrm{SO}_4^{2-}\)) acts as a counterion carrying a 2- charge. To balance this, the entire complex must have an overall charge of 2+. Water and nitric oxide as ligands contribute a net charge of zero. Thus, the iron's oxidation state must account for this charge, which in this case is +2. By carefully setting up the charge balance equation: \( x + 0 = +2 \), you can solve for the oxidation state, ensuring comprehensive understanding and application of charge balancing in coordination chemistry.