Problem 4 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Among statements (1) - (4), the correct ones are : [Main Sep. 04, 2020 (I)] (1) Lime stone is decomposed to \(\mathrm{CaO}\) during the extraction of iron from its oxides. (2) In the extraction of silver, silver is extracted as an anionic complex. (3) Nickel is purified by Mond's process. (4) \(\mathrm{Zr}\) and Ti are purified by Van Arkel method. (a) \((1),(2),(3)\) and (4) (b) (1), (3) and (4) only (c) (2), (3) and (4) only (d) (3) and (4) only

Step-by-Step Solution

Answer

All statements are correct. The correct option is (a) \((1),(2),(3)\) and (4).

Step 1: Analyze Statement (1)

Statement (1) discusses the decomposition of limestone to form \(\mathrm{CaO}\) during the extraction of iron from its oxides. Limestone (\(\mathrm{CaCO}_3\)) decomposes into \(\mathrm{CaO}\) and \(\mathrm{CO}_2\) when heated. The \(\mathrm{CaO}\) formed acts as a flux that helps in the removal of impurities. Hence, statement (1) is correct.

Step 2: Analyze Statement (2)

Statement (2) claims that in the extraction of silver, silver is extracted as an anionic complex. During the cyanidation process, silver forms a soluble complex of \(\text{[Ag(CN)}_2\text{]}^{-}\). Thus, statement (2) is correct.

Step 3: Analyze Statement (3)

Statement (3) suggests that nickel is purified by Mond's process. Mond's process involves converting nickel into a volatile complex (nickel tetracarbonyl), which is then decomposed to yield pure nickel. Therefore, statement (3) is correct.

Step 4: Analyze Statement (4)

Statement (4) indicates that \(\mathrm{Zr}\) and \(\mathrm{Ti}\) are purified by the Van Arkel method. This method is used for refining metals like zirconium and titanium through the formation of volatile iodides, which decompose to yield pure metals. Hence, statement (4) is correct.

Step 5: Determine the Correct Option

Now we assess all statements. Each one has been confirmed correct: statement (1), statement (2), statement (3), and statement (4) are all correct. Therefore, the correct option is (a) \((1),(2),(3)\) and (4).

Key Concepts

Limestone Decomposition

Limestone, chemically known as calcium carbonate (\( \mathrm{CaCO}_3 \)), decomposes when exposed to high temperatures. This process, known as calcination, is critical in metallurgical practices, specifically during the extraction of iron from its oxides. When limestone is heated, it breaks down into calcium oxide (\( \mathrm{CaO} \)) and carbon dioxide (\( \mathrm{CO}_2 \)). The resulting calcium oxide acts as a flux in metallurgy.
In iron extraction, the role of calcium oxide is to react with impurities such as silica (\( \mathrm{SiO}_2 \)), forming a slag that is easily removable. Hence, limestone decomposition not only facilitates the physical release of metal by creating space but also ensures metal purity by eliminating undesired compounds.

Cyanidation Process

The cyanidation process is pivotal in the extraction of precious metals like gold and silver. In this process, metals are dissolved using a solution of cyanide, which leads to the formation of soluble complexes.
For silver, the involving equation is:\[ \text{4Ag} + \text{8CN}^- + \text{2H}_2\text{O} + \text{O}_2 \rightarrow [\text{4Ag(CN)}_2]^- + \text{4OH}^- \]This equation illustrates how silver reacts with cyanide ions to produce a \( \text{Ag} \) anionic complex. The process is efficient because it enables the selective extraction of silver even from low-grade ores. The extracted metal complex can be subsequently processed to recover pure silver through precipitation or other means.

Mond's Process

Mond's process is an industrial purification method specifically designed for nickel. It leverages the unique properties of nickel to form a gaseous state under certain conditions.
The process begins by heating impure nickel with carbon monoxide (\( \mathrm{CO} \)) at 50-60 °C, forming nickel tetracarbonyl (\( \mathrm{Ni(CO)}_4 \)), a volatile compound. Once formed, the nickel carbonyl gas is then passed through at higher temperatures, where it decomposes back into pure nickel and carbon monoxide.

• The low temperature ensures only nickel reacts, isolating it from other impurities.
• The decomposition at elevated temperatures ensures the recovery of pure nickel.

This dual-temperature approach makes Mond's process efficient for obtaining high-purity nickel.

Van Arkel Method

The Van Arkel method is known for purifying metals like zirconium (\( \mathrm{Zr} \)) and titanium (\( \mathrm{Ti} \)), which are essential in various high-performance applications. This method is rooted in the formation of volatile iodide compounds.
Firstly, the impure metal is heated with iodine, forming volatile iodides:

• For titanium: \( \mathrm{Ti} + 2\mathrm{I}_2 \rightarrow \mathrm{TiI}_4 \)
• For zirconium: \( \mathrm{Zr} + 2\mathrm{I}_2 \rightarrow \mathrm{ZrI}_4 \)

These iodides are then decomposed on a hot filament (around 1800 °C), where the pure metal is deposited:

• \( \mathrm{TiI}_4 \rightarrow \mathrm{Ti} + 2\mathrm{I}_2 \)
• \( \mathrm{ZrI}_4 \rightarrow \mathrm{Zr} + 2\mathrm{I}_2 \)

This cycle ensures the extraction of high-purity metals by removing other non-volatile impurities, making it a celebrated purification process.