Problem 175 - A Complete Resource Book in Chemistry for JEE Main

Question

Which method of purification is represented by the following equation: \(\mathrm{Ti}(\mathrm{s})+2 \mathrm{I}_{2}(\mathrm{~g}) \stackrel{\mathrm{s23} \mathrm{K}}{\longrightarrow} \mathrm{Ti} \mathrm{I}_{4}(\mathrm{~g}) \stackrel{170 \mathrm{~K}}{\longrightarrow} \mathrm{Ti}(\mathrm{s})+2 \mathrm{I}_{2}(\mathrm{~g})\) (a) Poling (b) Cupellation (c) Zone refining (d) Van Arkel

Step-by-Step Solution

Answer

The method represented is (d) Van Arkel.

Step 1: Identify the Process Type

In the given equation, we need to recognize the process which involves the conversion and decomposition of a compound to purify an element. This is a clue to identify the type of purification method.

Step 2: Analyze the Chemical Equation

The chemical equation shows titanium (Ti) reacting with iodine (\(\mathrm{I}_2\)) to form titanium tetraiodide (\(\mathrm{TiI}_4\)) which is a gaseous compound. This gaseous compound decomposes back to pure titanium and iodine upon heating.

Step 3: Connect the Process to Known Purification Methods

The formation of a volatile compound (\(\mathrm{TiI}_4\)) and subsequent decomposition are key aspects of the Van Arkel method. This method is specifically used to purify titanium and zirconium by first converting them into their volatile iodides and then decomposing these iodides to obtain pure metal.

Step 4: Match the Description with Answer Choices

Review the answer choices provided: (a) Poling, (b) Cupellation, (c) Zone refining, (d) Van Arkel. Based on the analysis, the described purification using volatile iodides matches the description of the Van Arkel method.

Key Concepts

Van Arkel Method

The Van Arkel Method is a fascinating purification technique used primarily for refining metals like titanium and zirconium. In this method, the metal is made to react with iodine or another suitable halogen to form a volatile compound. This compound, often a tetraiodide, is then easily separable due to its volatility. When this compound is subsequently decomposed, it returns to a highly pure form of the original metal.

This process involves two major steps:

• Formation of the volatile iodide: The metal, such as titanium, reacts with iodine to form a compound like titanium tetraiodide (\(\mathrm{TiI}_4\)). The equation for the reaction looks like this: \[\mathrm{Ti(s)} + 2\,\mathrm{I}_2(g) \rightarrow \mathrm{TiI}_4(g)\]
• Decomposition: The volatile iodide is then decomposed back into the pure metal and iodine. This occurs upon heating under specific conditions: \[\mathrm{TiI}_4(g) \rightarrow \mathrm{Ti(s)} + 2\,\mathrm{I}_2(g)\]

The beauty of this method lies in its ability to produce highly pure metal through the reversible transformation, taking advantage of the volatility of the intermediate compound.

Titanium Purification

Purifying titanium is a crucial process, especially in industries requiring high-quality materials like aerospace, due to titanium's strength and corrosion resistance. The Van Arkel Method provides a reliable way to purify titanium to obtain a version almost free from impurities.

The key lies in the method's ability to transform titanium into titanium tetraiodide, a volatile compound. Since this tetraiodide is gaseous, it can be separated easily from solid impurities. Once isolated, the titanium tetraiodide undergoes decomposition back to pure titanium, leaving very little residue of impurities.

This method ensures that the titanium obtained is of a high purity level, which is essential for applications where even small impurities can lead to significant performance issues. By relying on chemical reactions and controlled decomposition, industries can produce highly refined titanium with consistent quality.

Volatile Compounds

Volatile compounds play a central role in a variety of purification methods, especially those involving the metal refinement process like the Van Arkel Method. These substances typically have a high vapor pressure at normal conditions, which means they can transition into a gas phase easily.

In the context of the Van Arkel Method, the formation of a volatile compound such as titanium tetraiodide allows effective separation from impurities. Here's why volatile compounds are crucial:

• Easy separation: Because they are in the gaseous phase, volatile compounds can be separated from non-volatile impurities present in the raw material.
• Reversibility: Once the volatile compound is isolated, it can be decomposed back to its original constituents, allowing recovery of the pure metal.
• High purity yields: As the reaction and decomposition proceed in controlled conditions, the impurities are left behind, resulting in highly pure end products.

The use of volatile compounds in purification processes highlights not just their chemical properties, but also their practical applications in producing materials with a purity suitable for advanced technological applications.