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

Question

Which method of purification is represented by the following equation: \(\mathrm{Ti}(\mathrm{s})+2 \mathrm{I}_{2}(\mathrm{~g}) \stackrel{\mathrm{S} 23 \mathrm{~K}}{\longrightarrow} \mathrm{Ti} \mathrm{I}_{4}(\mathrm{~g}) \stackrel{1 \pi 0 \mathrm{~K}}{\longrightarrow} \mathrm{Ti}(\mathrm{s})+2 \mathrm{I}_{2}(\mathrm{~g})\) (a) Poling (b) Cupellation (c) Zone refining (d) Van Arkel

Step-by-Step Solution

Answer

The method of purification is Van Arkel.

Step 1: Determine the process involved

The provided chemical equation represents a process involving the reaction of solid titanium (\(\mathrm{Ti(s)}\)) with iodine gas (\(\mathrm{I_2(g)}\)) to first form titanium(IV) iodide (\(\mathrm{TiI_4(g)}\)). This compound is then decomposed back into titanium and iodine.

Step 2: Identify the specific temperatures mentioned

Notice the temperatures indicated in the equation: the formation of \(\mathrm{TiI_4(g)}\) is done at a higher temperature (indicated as \(\mathrm{S} 23\ \mathrm{K}\)), and the decomposition occurs at a lower temperature (indicated as \(1 \pi 0\ \mathrm{K}\)). This corresponds to a process of heating and then cooling.

Step 3: Relate the process to purification methods

The process described in the equation is known as the Van Arkel method of refining, also called the iodide process, where titanium reacts with iodine to form volatile \(\mathrm{TiI_4}\). When \(\mathrm{TiI_4}\) is decomposed at a lower temperature, pure titanium is deposited.

Step 4: Select the correct method

The Van Arkel method specifically describes the purification of metals by forming a volatile compound and then decomposing it to obtain pure metal. As the process involves heating to form a compound and then decomposing it by cooling, option (d) Van Arkel is the correct choice.

Key Concepts

Metal Purification

The purification of metals is an essential process in material science and industry, ensuring we use high-quality materials in manufacturing. Metal purification involves removing impurities from raw metal to obtain a purer form.
Here are a few reasons why metal purification is important:

• Improved Properties: Pure metals typically have better electrical, thermal, and mechanical properties, which are required for high-performance applications.
• Enhanced Durability: Metals without impurities are less prone to corrosion and wear, leading to longer-lasting products.
• Increased Safety: Certain impurities can make metals brittle or prone to failure under stress, so purification reduces this risk.

Various methods exist for metal purification, including electrolysis, distillation, and the Van Arkel method. Choosing the right method often depends on the specific metal and the nature of the impurities.

Iodide Process

The iodide process, also known as the Van Arkel method, is a sophisticated technique used for purifying metals such as titanium and zirconium. It makes use of the volatility of certain metal iodides to separate the metal from its impurities.
Here's how the iodide process works:

• Initial Reaction: The metal reacts with iodine to form a volatile iodide compound. In the example of titanium, solid titanium (\( \mathrm{Ti(s)} \)) reacts with iodine (\( \mathrm{I_2(g)} \)) to form titanium(IV) iodide (\( \mathrm{TiI_4(g)} \)).
• Transport of Volatile Iodide: This volatile iodide is transported away from the impurity-containing reaction zone.
• Decomposition: The iodide is then decomposed at a lower temperature, usually on a heated filament, resulting in the deposition of pure metal and the release of iodine gas, which can be recycled.

This method is particularly advantageous for metals that have high melting points or require high purity for their applications. The ability to recycle iodine within the process also makes it an environmentally appealing choice.

Titanium Refining

Refining titanium is crucial due to its widespread use in various high-performance fields, including aerospace, medical devices, and marine applications. Titanium's ability to resist corrosion, along with its high strength-to-weight ratio, makes it a sought-after material in demanding environments.
Several methods can be used for refining titanium, but the Van Arkel method is common when high purity is required. Here's why titanium refining is important:

• Removing Impurities: Impurities such as oxygen, nitrogen, and carbon can significantly affect titanium's properties, like its ductility and strength.
• Maximizing Performance: High-purity titanium has superior mechanical properties, which are crucial for applications in aerospace and medical industries.
• Enhancing Compatibility: In medical applications, titanium must be virtually impurity-free to minimize risks of rejection or inflammation when used in implants.

The Van Arkel method ensures the production of extremely pure titanium by eliminating contaminants effectively, making the refined titanium suitable for critical applications where performance cannot be compromised.