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 in the compound is 2.

Step 1: Understand the Problem

We need to determine the oxidation state of iron (Fe) in the complex \[\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\mathrm{NO}\right] \mathrm{SO}_{4}. \] The compound comprises an iron complex cation \[\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\mathrm{NO}\right]^{+}\] and a sulfate anion \(\mathrm{SO}_{4}^{2-}\). The overall charge of the compound should be neutral.

Step 2: Determine the Charges of Ligands and Counter Ion

The water molecule (\(\mathrm{H_{2}O}\)) is a neutral ligand, contributing 0 charge each. The nitrosyl ligand (\(\mathrm{NO}\)) can contribute different charges depending on its bonding mode, but here it typically contributes -1. The overall charge of the complex ion is determined by balancing these charges with the sulfate ion. \(\mathrm{SO_4}^{2-}\) has a charge of -2.

Step 3: Apply Charge Balance

The charge on the complex ion \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\mathrm{NO}\right]^{+}\) is +1 because \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\mathrm{NO}\right]^{+}\) \(\mathrm{SO}_{4}^{2-}\) must balance to make the entire compound neutral. Since \(\mathrm{SO}_{4}^{2-}\) has a charge of -2, the cation must have a +1 charge to balance it.

Step 4: Calculate the Oxidation State of Iron

To determine the oxidation state of \(\mathrm{Fe}\), consider the charges: let oxidation state of \(\mathrm{Fe\) be \(x\). The equation becomes: \[x + 0(5) + (-1) = +1\]\(x\) - 1 = +1 implies \(x = 2\). Thus, the oxidation state of \(\mathrm{Fe}\) is +2.

Key Concepts

Complex Compounds

Complex compounds are fascinating entities in chemistry. They are made up of a central metal atom or ion surrounded by molecules or ions known as ligands. The overall structure forms a coordination entity, usually with specific geometric arrangements.
Understanding complex compounds involves recognizing the relationship between the central metal and its surrounding ligands. The bonding involves a coordinate covalent bond, where ligands donate electron pairs to the central metal atom.
Complex compounds exist in diverse forms such as coordination complexes, organometallic compounds, and bioinorganic complexes.

• Coordination complexes typically involve transition metals.
• These compounds can exhibit various oxidation states.
• They have practical applications in catalysis, bioinorganic chemistry, and as industrial catalysts.

By exploring complex compounds, we discover a rich field of chemistry that bridges work in both organic and inorganic areas, leading to innovations in scientific research and industry.

Coordination Chemistry

Coordination chemistry refers to the study of complex compounds, focusing on the interactions between central metal ions and ligands. This area of chemistry helps to understand how these interactions affect the properties and functions of the resulting compounds.
One of the key aspects of coordination chemistry is the **coordination number**. It indicates the number of ligand atoms that are directly bonded to the central atom. For example, in the complex \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\mathrm{NO}\right]\)SO_4, the coordination number for iron is 6.
Coordination compounds come in different shapes, such as octahedral, square planar, and tetrahedral arrangements. These geometries are determined by the number and type of ligands involved.

• Octahedral arrangements often involve six ligands.
• Square planar is common with four ligands.
• Tetrahedral occurs with four ligands, too, but has a different spatial arrangement.

Understanding these concepts is crucial for predicting the structures and reactivity of coordination compounds, which can further aid in designing new compounds with desired properties.

Ligands in Chemistry

Ligands are essential components of complex compounds. They are molecules or ions that can donate one or more pairs of electrons to the central metal atom or ion. This donation forms coordinate covalent bonds, stabilizing the metal center within the complex.
Ligands play a vital role in defining the nature and properties of a coordination complex. Their size, charge, and electron-donating ability can influence the complex's stability, reactivity, and color.
There are several types of ligands based on their ability to donate electrons:

• **Monodentate ligands** are those that donate one pair of electrons. Water (\(H_2O\)) is an example of a monodentate ligand.
• **Bidentate ligands** can donate two pairs of electrons from two donor atoms.
• **Polydentate ligands**, such as EDTA, can form multiple bonds with the central metal.

In the example compound \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\mathrm{NO}\right]\)SO_4, water acts as a neutral monodentate ligand, and nitrosyl (\(NO\)) is known for its ability to bind in different modes, often contributing a negative charge.
Recognizing the influence of ligands on coordination complexes enhances our understanding of their structural and functional diversity, which is fundamental in fields ranging from synthetic chemistry to biological systems.