Problem 100 - A Complete Resource Book in Chemistry for JEE Main

Question

What product is formed by mixing the solution of \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) with the solution of \(\mathrm{FeCl}_{3} ?\) (a) ferro-ferricyanide (b) ferric-ferrocyanide (c) ferri-ferricyanide (d) none of these

Step-by-Step Solution

Answer

The product is ferric ferrocyanide.

Step 1: Write the Chemical Equation

We need to identify the reaction between \( \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \) and \( \mathrm{FeCl}_3 \). The reaction typically results in a double displacement reaction: \[ \text{\[\mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6]\]} + 4 \text{\[\mathrm{FeCl}_3\]} \rightarrow \text{\[\mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3\]} + 12 \text{\[\mathrm{KCl}\]} \]

Step 2: Identify the Products Formed

The key product formed is \( \mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3 \), known as Prussian blue, a ferric ferrocyanide. The other product is \( \mathrm{KCl} \), potassium chloride.

Step 3: Relate Products to Given Options

From the given options, option (b) matches \( \mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3 \) as a ferric ferrocyanide, which indicates that the answer to the question is option (b).

Key Concepts

Double Displacement Reactions

Chemical reactions can take various forms, one of which is the double displacement reaction. This occurs when parts of two compounds swap places to form two new compounds. The basic form of a double displacement reaction can be represented as: \[ \text{AB} + \text{CD} \rightarrow \text{AD} + \text{CB} \]In this notation, AB and CD are reactants, while AD and CB are the products. This reaction is also commonly referred to as a metathesis reaction.

• Double displacement reactions are especially common in solution chemistry.
• They often result in the formation of a precipitate, a gas, or water.

In the reaction between \( \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \) and \( \mathrm{FeCl}_3 \), both compounds dissociate into ions in a solution. When they recombine, they form ferric ferrocyanide (Prussian blue) and potassium chloride, showcasing a classic example of a double displacement reaction.

Prussian Blue

Prussian blue is a fascinating compound with historical and practical significance. It is known for its intense blue color and was one of the first synthetic pigments used in painting.

• Prussian blue is chemically known as ferric ferrocyanide.
• It is composed of iron(III) ions bonded to ferrocyanide ions.

Aside from its role as a pigment, Prussian blue has important applications:

• It is used in medical treatments, specifically as an antidote for certain kinds of heavy metal poisoning.
• Its vibrant color finds use in inks and as a dye for textiles.

The formation of Prussian blue in reactions like the one between \( \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \) and \( \mathrm{FeCl}_3 \) is a wonderful example of chemical artistry, where molecular interactions result in striking visual transformations.

Ferric Ferrocyanide

Ferric ferrocyanide, scientifically known as \( \mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3 \), is more commonly referred to as Prussian blue. It is an insoluble compound featuring a complex crystalline structure. The structure consists of iron ions in different oxidation states, creating a robust lattice.

• This compound uniquely bridges organic and inorganic chemistry through its metal-cyanide bonds.
• Its solid structure results not only in its distinct color but also in its low solubility in water.

Ferric ferrocyanide is created through double displacement reactions like the one discussed, demonstrating the power of chemical bonds. Understanding its formation allows us to appreciate how slight changes in chemical structure influence both the physical and chemical properties of a compound. Besides its use as a pigment, ferric ferrocyanide continues to be studied for its potential across various scientific fields.