Problem 7 - A Complete Resource Book in Chemistry for JEE Main

Question

Ferric iron forms a prussian blue coloured precipitate with \(\mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})]\), due to the formation of (a) \(\left.\mathrm{Fe}_{4}[\mathrm{Fe}(\mathrm{CN})]_{6}\right]_{3}\) (b) \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) (c) \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) (d) \(\mathrm{Fe}(\mathrm{CNS})_{3}\)

Step-by-Step Solution

Answer

Option (a) ext{Fe}_{4}[ ext{Fe}( ext{CN})_{6}]_{3} n forms the prussian blue precipitate.

Step 1: Understanding the Reaction

Ferric iron ( ext{Fe}^{3+} n) reacts with potassium ferrocyanide ( ext{K}_{4}[ ext{Fe}( ext{CN})_{6}] n) to form a prussian blue colored compound. The ferric ion acts as an oxidizing agent, converting ferrocyanide to ferricyanide.

Step 2: Identifying the Product

In the reaction, ext{Fe}^{3+} n combines with ext{Fe}( ext{CN})_{6}^{4-} n from ext{K}_{4}[ ext{Fe}( ext{CN})_{6}] n to form a complex compound, ext{Fe}_{4}[ ext{Fe}( ext{CN})_{6}]_{3} n, which is responsible for the prussian blue color.

Step 3: Analyzing the Options

Review each given option: a) ext{Fe}_{4}[ ext{Fe}( ext{CN})_{6}]_{3} n is indeed the prussian blue precipitate. b) ext{K}_{4}[ ext{Fe}( ext{CN})_{6}] n is the starting material, not the product. c) ext{K}_{3}[ ext{Fe}( ext{CN})_{6}] n is unrelated to this reaction. d) ext{Fe}( ext{CNS})_{3} n is not a product of this reaction.

Step 4: Selecting the Correct Answer

Based on the analysis, option (a), ext{Fe}_{4}[ ext{Fe}( ext{CN})_{6}]_{3} n, is the correct answer as it indicates the prussian blue precipitate formed in the reaction.

Key Concepts

Ferric Iron

Ferric iron, represented as \( \mathrm{Fe}^{3+} \), plays a pivotal role in various chemical reactions. It is an oxidized form of iron and is known for its ability to attract negatively charged components due to its positive charge. In the context of Prussian Blue formation, ferric iron is crucial as it participates actively in creating this intensely colored compound.

The process begins when ferric iron encounters potassium ferrocyanide. The ferric ion acts as an oxidizing agent. This means it aids in transferring electrons, which facilitates the conversion of ferrocyanide into ferricyanide. The combination of these elements is what leads to the distinctive blue shade of the Prussian Blue compound.

In addition to acting as a key participant in color formation, ferric iron's properties are significant in various industrial and laboratory processes. Whether it be in water purification or as a catalyst in chemical synthesis, understanding ferric iron's behavior is essential for chemists.

Potassium Ferrocyanide

Potassium ferrocyanide is represented by the chemical formula \( \mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}] \). This compound is crucial to understand when learning about Prussian Blue. This is because it serves as the starting material and reacts with ferric ions to form the complex end product.

Unlike what its name might suggest, potassium ferrocyanide is not highly toxic. It is quite stable and is used in a range of processes, such as in the sensitive detection of iron and in photographic processing. Its chemistry involves a central iron(II) ion surrounded by six cyanide groups in an octahedral structure, making it a strong complexing agent.

When ferric ions are introduced, the interaction with potassium ferrocyanide results in the formation of ferricyanide ions. This is a necessary step in producing the dazzling Prussian Blue, highlighting potassium ferrocyanide's important role as both a reagent and participant in iron chemistry.

Complex Compound Formation

Complex compound formation is a fascinating aspect of inorganic chemistry. A complex is formed when metal ions bond with ligands, which are ions or molecules that donate electron pairs to the metal. In the case of Prussian Blue, such intricate bonding leads to its unique properties and color.

The specific reaction between ferric ions and potassium ferrocyanide results in the formation of \( \mathrm{Fe}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}]_{3} \), a complex compound that showcases Prussian Blue's characteristic deep color. This compound is an example of how metal-ligand interactions can produce a new substance with distinct physical and chemical properties.

For students and enthusiasts, delving into complex compound formation offers insights into the molecular mechanics that dictate how substances interact and behave. These concepts are foundational for understanding not only Prussian Blue but also the formation of various other coordination compounds critical in industry and research.