Problem 124 - A Complete Resource Book in Chemistry for JEE Main

Question

Anhydrous ferric chloride is prepared by (a) heating hydrated ferric chloride at a high temperature in a stream of air (b) heating metallic iron in a stream of dry chlorine gas (c) reaction of ferric oxide with hydrochloric acid (d) reaction of metallic iron with hydrochloric acid

Step-by-Step Solution

Answer

Option (b): heating metallic iron in a stream of dry chlorine gas produces anhydrous ferric chloride.

Step 1: Understanding the Problem

The problem requires us to identify the correct method for preparing anhydrous ferric chloride from the given options. We need to evaluate each method to determine if it results in the formation of anhydrous ferric chloride.

Step 2: Evaluating Option (a)

Option (a) suggests heating hydrated ferric chloride in a stream of air. This method would actually lead to the loss of water from hydrated ferric chloride, but it does not effectively lead to the formation of pure anhydrous ferric chloride due to possible hydrolysis.

Step 3: Evaluating Option (b)

Option (b) involves heating metallic iron in a stream of dry chlorine gas. This method is a known industrial process where chlorine gas reacts with iron to form ferric chloride. The reaction is as follows: \[2Fe + 3Cl_2 ightarrow 2FeCl_3\] This method effectively produces anhydrous ferric chloride.

Step 4: Evaluating Option (c)

Option (c) suggests reacting ferric oxide with hydrochloric acid. This reaction forms hydrated ferric chloride, not the anhydrous form, through the equation: \[Fe_2O_3 + 6HCl ightarrow 2FeCl_3 imes 6H_2O\] Therefore, it does not produce anhydrous ferric chloride.

Step 5: Evaluating Option (d)

Option (d) involves reacting metallic iron with hydrochloric acid. This reaction yields ferrous chloride and hydrogen gas rather than ferric chloride. \[Fe + 2HCl ightarrow FeCl_2 + H_2\] Therefore, this method does not produce anhydrous ferric chloride.

Step 6: Selecting the Correct Answer

After analyzing all options, option (b) is identified as the correct method for preparing anhydrous ferric chloride. It involves the reaction of metallic iron with dry chlorine gas, resulting in the desired compound.

Key Concepts

Ferric Chloride

Ferric chloride, also known as iron(III) chloride, is a versatile chemical compound with the formula \(FeCl_3\). It has significant industrial uses, particularly in water treatment and manufacturing. This dark brown solid is categorized as "anhydrous" when it is free from water molecules, which is crucial for certain applications.

Ferric chloride is highly effective in removing impurities in water treatment due to its ability to form coagulants. These coagulants aggregate small colloidal particles into larger clusters for easier removal. In industry, it is also used as an etchant in the production of printed circuit boards (PCBs). Both of these applications require a specific chemical form, which largely depends on how the ferric chloride is prepared.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into different substances, known as products. These reactions are essential to form compounds like anhydrous ferric chloride.

Understanding chemical equations provides insight into the stoichiometry of a reaction. For ferric chloride, the main reaction involves combining metallic iron and chlorine gas, as shown:

• \(2Fe + 3Cl_2 \rightarrow 2FeCl_3\)

This equation highlights the reactants and the conditions needed to achieve the desired ferric chloride. Each component plays a crucial role, requiring specific conditions such as the presence of dry chlorine gas to ensure the formation of anhydrous ferric chloride.

Industrial Chemistry

Industrial chemistry involves the application of chemical processes on a commercial scale, ensuring efficiency and scalability. It examines how substances like ferric chloride are produced and utilized in bulk.

To produce anhydrous ferric chloride industrially, specific reactions must be carefully controlled. Utilizing dry chlorine gas in an environment devoid of water is crucial to avoid producing hydrated forms. The reactions are typically carried out at high temperatures to facilitate complete conversion. This ensures the purity and effectiveness of the final product used in various industrial applications.

Chlorine Gas

Chlorine gas is a critical component for the synthesis of anhydrous ferric chloride. Chlorine is a greenish-yellow gas with a strong odor, usually used for its reactive ability with metals like iron.

When used in the reaction to produce ferric chloride, chlorine gas must be dry to prevent undue formation of hydrates. This is crucial as even minimal exposure to water can lead to hydrolysis, forming byproducts that complicate the anhydrous compound's preparation. Industrial setups ensure that chlorine is inaccessible to moisture during transportation and reaction stages.

Hydrochloric Acid

Hydrochloric acid (HCl) is a vital industrial chemical commonly encountered in various synthesis and cleaning processes. However, when it comes to anhydrous ferric chloride preparation, its role is indirect.

While hydrochloric acid can react with iron to produce iron(II) chloride (\(FeCl_2\)), this process is not used for the direct production of anhydrous ferric chloride. The reaction of iron with hydrochloric acid yields hydrogen gas and iron(II) chloride, neither of which are desired in the direct production of anhydrous ferric chloride:

• \(Fe + 2HCl \rightarrow FeCl_2 + H_2\)

Thus, while hydrochloric acid is essential for other processes, it does not facilitate the formation of iron(III) chloride in its anhydrous form.

Iron Metal

Iron metal, commonly symbolized as \(Fe\), is a key element in the manufacture of anhydrous ferric chloride. As a ductile and malleable element, its reactive properties make it suitable for various chemical processes.

In preparing ferric chloride, iron reacts with chlorine gas under controlled conditions. The metal needs to be pure and free from contaminants that could interfere with the reaction process. Industrially, fine iron particles or iron filings are often used to increase surface area, thus facilitating a more efficient reaction with chlorine gas. This interaction forms the anhydrous ferric chloride essential for many industrial applications.