Problem 85 - 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) is correct: heating metallic iron in a stream of dry chlorine gas.

Step 1: Interpret the options

We need to find how anhydrous ferric chloride ( FeCl_3 ) can be prepared from the given methods. We have four methods (a) to (d) to evaluate.

Step 2: Evaluate option (a)

Heating hydrated ferric chloride ( FeCl_3 ullet 6H_2O ) at a high temperature would typically result in the loss of water but may lead to decomposition into other products in the presence of air, rather than yielding anhydrous FeCl_3 .

Step 3: Evaluate option (b)

Heating metallic iron ( Fe ) in a stream of dry chlorine gas ( Cl_2 ) results in a direct chemical reaction that forms anhydrous ferric chloride ( FeCl_3 ): Fe + 3Cl_2 ightarrow 2FeCl_3.

Step 4: Evaluate option (c)

The reaction of ferric oxide ( Fe_2O_3 ) with hydrochloric acid ( HCl ) would produce hydrated ferric chloride due to water from the acid. Thus, this method would not yield anhydrous FeCl_3 .

Step 5: Evaluate option (d)

Reacting metallic iron ( Fe ) with hydrochloric acid ( HCl ) gives ferrous chloride ( FeCl_2 ) and hydrogen gas ( H_2 ), which does not produce ferric chloride directly.

Step 6: Determine the best method

Based on the analysis, option (b), heating metallic iron in a stream of dry chlorine gas, is the only method that effectively produces anhydrous ferric chloride ( FeCl_3 ).

Key Concepts

Understanding Chemical Reactions

Chemical reactions play a crucial role in the transformation of substances. They occur when substances, called reactants, undergo a rearrangement of their atoms to form new substances, known as products.
In the context of this exercise, we focus on the preparation of anhydrous ferric chloride (\(FeCl_3\)). This process is a classic example of a synthesis reaction, where simpler substances combine to form a more complex product.

• Reacting substances: metallic iron (\(Fe\)) and chlorine gas (\(Cl_2\)).
• Product formed: anhydrous ferric chloride (\(FeCl_3\)).

During the reaction, iron atoms lose electrons to become positively charged iron ions, bonding with chlorine ions. The balanced chemical equation for the reaction is:\[Fe + 3Cl_2 \rightarrow 2FeCl_3\]The reaction requires sufficient contact between the reactants, typically provided by heating, which helps in breaking and forming new chemical bonds, completing the synthesis of \(FeCl_3\).

Role of Metallic Iron in the Reaction

Metallic iron plays a vital role as a reactant in the formation of anhydrous ferric chloride. Iron is a transition metal, known for its ductility, malleability, and electrical conductivity. These properties are advantageous in various industrial applications. When iron is heated in the presence of dry chlorine gas, it provides the necessary electrons for the chemical reaction, transforming into iron ions.

• Iron's electron configuration allows it to lose electrons and participate actively in redox reactions.
• In this process, each iron atom loses three electrons and joins with three chlorine molecules to form ferric chloride.

The change in oxidation state as iron transitions from metallic form to ionic form is central to the oxidation process. This characteristic makes metallic iron a suitable candidate for creating compounds like \(FeCl_3\) through direct synthesis.

Chlorine Gas in Synthesis

Chlorine gas, a greenish-yellow diatomic molecule, is an essential element in chemical manufacturing. It is highly reactive, which makes it particularly useful in synthesizing numerous compounds.

• As a halogen, chlorine gas (\(Cl_2\)) accepts electrons to complete its electron shell and forms chloride ions (\(Cl^-\)).
• During the reaction with iron, it acts as an oxidizing agent, facilitating the conversion of iron to its ionic form.

The dry state of chlorine is critical for forming anhydrous ferric chloride. The presence of moisture can lead to the formation of hydrated forms instead. Ensuring the chlorine is dry helps to prevent unwanted side reactions and facilitates the creation of the desired anhydrous product.
The efficiency of this reaction also relies on the controlled exposure of iron to chlorine gas, maximizing yield and purity.