Problem 50 - A Complete Resource Book in Chemistry for JEE Main

Question

Perssian blue is formed when (a) ammonium sulphate reacts with \(\mathrm{FeCl}_{3}\) (b) ferrous sulphate reacts with \(\mathrm{FeCl}_{3}\) (c) ferrous ammonium sulphate reacts with \(\mathrm{FeCl}_{3}\) (d) ferric sulphate reacts with \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\)

Step-by-Step Solution

Answer

Persian blue is formed by (d) ferric sulphate reacting with \( \mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \).

Step 1: Understanding the Problem

We need to determine which reaction produces Persian blue. Persian blue is another name for Prussian blue, which is a dark blue pigment.

Step 2: Review Chemical Reactions

Prussian blue is a dark blue pigment formed by the reaction of ferric ions with ferrocyanide ions. This occurs commonly when \( ext{Fe}^{3+} \) ions from ferric salts react with \( ext{Fe(CN)}_6^{4-} \).

Step 3: Match with Given Options

Option (d) involves the reaction of ferric sulphate with \( ext{K}_4[ ext{Fe(CN)}_6] \). In this reaction, \( ext{Fe}^{3+} \) from ferric sulphate reactive with ferrocyanide ions \( ext{Fe(CN)}_6^{4-} \) from potassium ferrocyanide, which forms Prussian blue.

Step 4: Verification with Knowledge

The formation of Prussian blue involves the creation of a complex iron cyanide compound from ferric ions and ferrocyanide ions, which aligns perfectly with option (d). Thus, option (d) is the correct selection.

Key Concepts

Ferric Ions

Ferric ions, denoted as \( \text{Fe}^{3+} \), are a key component in the formation of Prussian blue. These ions are derived from ferric salts, such as ferric chloride (\( \text{FeCl}_3 \)) or ferric sulfate. They are trivalent, meaning they carry a three positive charge. This allows them to easily interact with negatively charged ions like ferrocyanide.

• Originates from ferric salts
• Carries a +3 charge
• Reacts with negative ions

When ferric ions come into contact with ferrocyanide ions, an ionic bond forms. This is a key step in creating the vibrant color of Prussian blue. The ability of ferric ions to form such stable complexes makes them integral in the synthesis of various complex compounds in chemistry.

Ferrocyanide Ions

Ferrocyanide ions, expressed as \( \text{Fe(CN)}_6^{4-} \), serve a pivotal role in the creation of Prussian blue. These ions are the counterparts to ferric ions in the formation process of this striking blue pigment. They carry a -4 charge, which allows them to easily pair with positively charged ions.

• Have a -4 charge
• Work in tandem with \( \text{Fe}^{3+} \) ions
• Originate from potassium ferrocyanide \( \text{K}_4[\text{Fe(CN)}_6] \)

Ferrocyanide ions stem from compounds like potassium ferrocyanide, where they're typically bound with potassium ions. When these ions combine with ferric ions, they form a highly stable complex, which is central to the production of Prussian blue. This interaction highlights the importance of ferrocyanide ions in both industrial and artistic contexts, given their role in producing various pigments and dyes.

Complex Iron Cyanide Compound

The formation of Prussian blue involves the creation of a complex iron cyanide compound. This compound results from the interaction between ferric ions and ferrocyanide ions. As these ions combine, they create a lattice structure characterized by the deep blue color known as Prussian blue.

• Combines \( \text{Fe}^{3+} \) and \( \text{Fe(CN)}_6^{4-} \) ions
• Results in a stable lattice structure
• Known for its vivid blue hue

The ability of these ions to form such a stable compound stems from strong ionic interactions and bonding within the lattice. This process is not only of significance chemically but also historically and culturally, as Prussian blue was one of the first synthetic pigments, widely used in arts and industry. Understanding the formation of this complex provides insight into diverse applications ranging from artistic expression to scientific innovation.