Problem 63 - A Complete Resource Book in Chemistry for JEE Main

Question

In nitroprusside ion, the iron and NO exist as \(\mathrm{Fe}^{\mathrm{ll}}\) and \(\mathrm{NO}^{+}\)rather than \(\mathrm{Fe}^{\mathrm{lH}}\) and NO. These forms can be differentiated by (a) estimating the concentration of iron (b) measuring the concentration of \(\mathrm{CN}^{-}\) (c) measuring the solid state magnetic moment (d) thermally decomposing the compound

Step-by-Step Solution

Answer

Measuring the solid-state magnetic moment (option c) differentiates the iron and NO forms.

Step 1: Identify the forms of iron and NO

In the nitroprusside ion, we need to differentiate between the forms \( \mathrm{Fe}^{II} \) and \( \mathrm{Fe}^{III} \) as well as \( \mathrm{NO}^+ \) and \( \mathrm{NO} \). The problem states that the correct forms are \( \mathrm{Fe}^{II} \) and \( \mathrm{NO}^+ \).

Step 2: Assess each option given

We have four options to help differentiate between these forms: (a) estimating the concentration of iron, (b) measuring the concentration of \( \mathrm{CN}^- \), (c) measuring the solid-state magnetic moment, and (d) thermally decomposing the compound.

Step 3: Evaluate the magnetic moment

\( \mathrm{Fe}^{II} \) and \( \mathrm{Fe}^{III} \) have different numbers of unpaired electrons, which affect their magnetic properties. \( \mathrm{Fe}^{II} \) (low-spin in nitroprusside) is diamagnetic, meaning it has no unpaired electrons, while \( \mathrm{Fe}^{III} \) would have unpaired electrons, making it paramagnetic. This difference can be detected by measuring the magnetic moment.

Step 4: Choose the most appropriate method

Option (c), measuring the solid-state magnetic moment, allows us to determine the oxidation state of iron by identifying whether the compound is diamagnetic or paramagnetic. This helps differentiate \( \mathrm{Fe}^{II} \) from \( \mathrm{Fe}^{III} \) effectively.

Key Concepts

Oxidation States of Iron

Understanding the oxidation states of iron is crucial in determining its chemical behavior and electronic configuration. Iron (Fe) typically exhibits oxidation states of +2 and +3. This essentially means that iron can lose either two or three electrons to form positive ions:

• Fe^{2+}: Formed by the loss of two electrons, this oxidation state is common in compounds where iron bonds with other elements through ionic or some polar covalent bonds. It's often found in biologically important compounds like hemoglobin.
• Fe^{3+}: Results from the loss of three electrons. This state is highly stable in many compounds due to the full or half-full dre subshell in a complex.

In the nitroprusside ion, Fe is in the +2 state (as Fe^{II}), meaning it has lost two electrons. This distinction is important when differentiating between iron oxidation states because each state has different physical and chemical properties, including magnetic characteristics.
Detecting these properties helps in analyzing and confirming the specific iron form present in a compound.

Magnetic Moment Measurement

Magnetic moment measurements are a pivotal method in identifying the oxidation state of iron in coordination compounds. Because the magnetic properties of a substance are affected by the presence of unpaired electrons, we can learn about the oxidation state by assessing whether the substance is diamagnetic or paramagnetic.

• Diamagnetism: Materials that have all paired electrons. They exhibit no nett magnetic field and are lightly repelled by a magnetic field. For instance, in the nitroprusside ion, Fe{II} exhibits low-spin characteristics, making it diamagnetic.
• Paramagnetism: Occurs in substances where there's at least one unpaired electron. Such materials are attracted to magnetic fields. Fe{III}, which usually has unpaired electrons, is an example of a paramagnetic state.

Measuring the magnetic moment allows chemists to understand the arrangement of electrons in a metal complex, enabling differentiation between states like Fe{II} and Fe{III}. This is crucial in analyses involving coordination compounds like the nitroprusside ion.

Differentiation of NO and NO+

The difference between NO (nitric oxide) and NO+ (nitrosyl cation) can be subtle but significant, especially in coordination chemistry. When it's part of a complex ion, like in nitroprusside, differentiating between these forms is crucial for understanding the compound's properties:

• NO (Nitric Oxide): Neutral molecule consisting of a nitrogen atom bonded to an oxygen atom, shared electrons include one unpaired electron making it a radical. This results in a unique reactivity profile.
• NO+ (Nitrosyl Cation): Formed by the loss of an electron from NO. This cationic form involves a full electron pair bond between nitrogen and oxygen with a linear structure, giving it different reactivity and bonding preferences in coordination environments.

The presence of NO+ instead of NO in the nitroprusside ion affects both the geometry and electron-distribution in the complex, influencing its stability and properties.

Coordination Compounds Chemistry

Coordination chemistry involves the study of complexes where a central metal atom is surrounded by molecules or ions called ligands. These interactions are crucial for the characteristics and reactivity of the coordination compound.

• Ligands: These can be neutral molecules like water or ammonia or ions like chloride or the nitrosyl cation (NO{+}). They donate electron pairs to the central atom, forming coordinate bonds and stabilizing the metal.
• Coordination Number: Refers to the number of ligand donor atoms bonded to the central metal. This determines the geometry of the complex. For example, octahedral geometry forms when there are six ligands, which is common in iron complexes.
• Stability of Complexes: Depends on factors like the charge, type of ligands, and electronic configuration of the metal. Strong field ligands like cyanide can cause low-spin configurations, affecting magnetic properties.

Understanding these fundamental aspects helps chemists predict the behavior and properties of compounds like the nitroprusside ion, where intricate metal-ligand interactions are present.