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

Short answer

The product is ferric-ferrocyanide (b).

Step-by-step solution

Identify Reactants

The reactants are potassium ferrocyanide \( \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \) and iron(III) chloride \( \mathrm{FeCl}_3 \). These will react to form a precipitate.

Determine Reaction Product

When \( \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \) reacts with \( \mathrm{FeCl}_3 \), an insoluble complex precipitate is formed, which is known as Prussian blue. The chemical formula for Prussian blue is \( \mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3 \), representing ferric-ferrocyanide.

Analyze Answer Options

The options given are (a) ferro-ferricyanide, (b) ferric-ferrocyanide, (c) ferri-ferricyanide, and (d) none of these. Since the product is Prussian blue, we are looking for 'ferric-ferrocyanide'.

Key concepts

Potassium Ferrocyanide

Potassium Ferrocyanide, with the chemical formula \( \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \), is a coordination compound that contains potassium ions and ferrocyanide ions. Its structure consists of a central iron atom surrounded by six cyanide ions, forming a stable complex.
It is part of the family of compounds known as ferrocyanides, which are generally cyanide complexes that contain iron. Despite containing cyanide groups, potassium ferrocyanide is considered non-toxic and safe enough to be used in various industries, mainly due to the strong bonding between iron and cyanides.
In chemistry experiments, it is often used to demonstrate complex ion reactions because it forms distinctive color changes when reacting with different metal ions. It is crucial for understanding coordination chemistry and serves as a fundamental example of how ligands can stabilize central metal ions in solution.

Iron(III) Chloride

Iron(III) chloride, also known as ferric chloride, has the chemical formula \( \mathrm{FeCl}_3 \). It is a compound made up of iron and chloride ions. This compound is highly soluble in water and forms acidic solutions, which have a characteristic yellow or brown coloration.
As an important reagent in chemistry, iron(III) chloride is often involved in oxidation reactions and is used in water treatment processes to remove impurities. In the context of chemical reactions, its role is often to provide iron(III) ions, which can then participate in the formation of complex precipitates, such as Prussian blue, when combined with other anions.
Its reactive nature makes it an excellent choice for experiments demonstrating precipitation reactions, allowing students to visually grasp the process of forming solid compounds from a solution.

Prussian Blue Formation

The formation of Prussian blue is a fascinating example of a precipitation reaction. When solutions of potassium ferrocyanide and iron(III) chloride are mixed, they react to produce Prussian blue, a deep blue pigment. The reaction can be represented by the equation:
\[4 \mathrm{FeCl}_3 + 3 \mathrm{K}_4[\mathrm{Fe}(\mathrm{CN})_6] \rightarrow \mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3 + 12\mathrm{KCl} \]
The reaction product, Prussian blue, has the chemical formula \( \mathrm{Fe}_4[\mathrm{Fe}(\mathrm{CN})_6]_3 \). This pigment has historical significance, being used in art and dyeing since the early 18th century.
The deep blue color is due to the complex structure of Prussian blue, where iron atoms in different oxidation states create electron interactions that absorb certain wavelengths of light, resulting in the appearance of blue. Understanding Prussian blue formation not only enriches chemistry knowledge but also illustrates the application of coordination compounds in everyday materials.

Ferric-Ferrocyanide

Ferric-ferrocyanide is the chemical name for Prussian blue, highlighting its composition of iron in different oxidation states. It is an example of a mixed-valence compound, which plays a significant role in its coloring properties.
Within ferric-ferrocyanide, iron exists in two different states: ferrous (\( \mathrm{Fe}^{2+} \)) and ferric (\( \mathrm{Fe}^{3+} \)). These iron ions are bridged by the cyano groups, forming a large network. This structure is responsible for its insolubility in water and its ability to form a precipitate.
Prussian blue, or ferric-ferrocyanide, doesn't dissolve easily in water, so when it forms during the reaction, it precipitates out of the solution, making it easy to identify visually. This property is particularly useful in pigment applications, water treatment, and demonstrating the principles of precipitation in chemical education.