Problem 97 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the reaction that does not take place during smelting process of copper extraction. (a) \(\mathrm{FeO}+\mathrm{SiO}_{2} \rightarrow \mathrm{FeSiO}_{3}\) (b) \(\mathrm{Cu}_{2} \mathrm{O}+\mathrm{FeS} \rightarrow \mathrm{Cu}_{2} \mathrm{~S}+\mathrm{FeO}\) (c) \(2 \mathrm{FeS}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{FeO}+2 \mathrm{SO}_{2}\) (d) \(2 \mathrm{Cu}_{2} \mathrm{~S}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{Cu}_{2} \mathrm{O}+2 \mathrm{SO}_{2}\)

Step-by-Step Solution

Answer

Reaction (b) does not take place during copper smelting.

Step 1: Understand Smelting Process

The smelting process of copper involves several chemical reactions that transform copper ore (usually copper sulphide) into pure copper. The key reactions include the roasting of sulphide ores to produce oxides, which are then reduced and smelted with other reacting substances to extract the metal.

Step 2: Analyze Reaction (a)

Reaction (a) is: \(\mathrm{FeO}+\mathrm{SiO}_{2} \rightarrow \mathrm{FeSiO}_{3}\). This reaction describes the formation of a slag component, which is the typical step in the extraction process to remove impurities. It is a valid part of the smelting process.

Step 3: Analyze Reaction (b)

Reaction (b) is: \(\mathrm{Cu}_{2} \mathrm{O}+\mathrm{FeS} \rightarrow \mathrm{Cu}_{2}\mathrm{~S}+\mathrm{FeO}\). This reaction describes an interaction between copper(I) oxide and iron(II) sulfide, forming copper(I) sulfide and iron(II) oxide. This is a reversal or undesirable reaction in smelting since it regenerates sulfide and does not yield pure copper.

Step 4: Analyze Reaction (c)

Reaction (c) is: \(2 \mathrm{FeS}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{FeO}+2 \mathrm{SO}_{2}\). This reaction describes the oxidation of iron (II) sulfide to form iron (II) oxide and sulfur dioxide. It is a typical step for removing iron as part of the process.

Step 5: Analyze Reaction (d)

Reaction (d) is: \(2 \mathrm{Cu}_{2} \mathrm{~S}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{Cu}_{2} \mathrm{O}+2 \mathrm{SO}_{2}\). This reaction represents the oxidation of copper (I) sulfide to form copper (I) oxide and sulfur dioxide, which is a valid step in the extraction process to further oxidize sulfur.

Step 6: Identify the Odd Reaction

Given these analyses, reaction (b) is the one that does not fit with the copper smelting process, as it does not contribute to the extraction of pure copper, but instead generates copper sulfide again.

Key Concepts

Smelting Process

Smelting is a crucial step in the extraction of copper, where the goal is to convert raw ore into pure metal. The process typically begins with treating the ore, which often contains copper sulfide, in a furnace at high temperatures. During smelting, several reactions occur alongside the generation of heat:

• Roasting: This is where the copper sulfide ore is heated in the presence of oxygen to form copper(I) oxide while releasing sulfur dioxide.
• Reduction: After forming the oxide, you reduce it to obtain pure copper while also removing impurities.

In the smelting of copper ore, it must be ensured that all sulfides are converted to oxides and subsequently reduced to yield copper. Sometimes other materials, known as fluxes, are used to aid the process and improve the recovery of the metal from the ore.

Chemical Reactions

Chemical reactions play a pivotal role in the copper extraction process, creating a chain of transformations within the furnace. Each step must happen in a specific sequence to achieve the desired purity of copper. The paramount reactions include:

• Conversion of sulfides to oxides, such as in the case of copper(I) sulfide reacting with oxygen to form copper(I) oxide and sulfur dioxide.
• The ongoing reduction processes that follow the initial reactions, where oxides are reduced to acquire the pure metal.
• Undesirable reactions, like reaction (b) \(\mathrm{Cu}_{2} \mathrm{O}+\mathrm{FeS} \rightarrow \mathrm{Cu}_{2} \mathrm{~S}+\mathrm{FeO}\), which need to be minimized as they revert the system back to the undesired sulfide form, hindering the extraction of pure copper.

The careful management and balance of these reactions are essential for successful copper extraction.

Impurities Removal

During the smelting process, various impurities present in the ore must be removed to achieve a high purity level in the final copper product. Part of the art of smelting is knowing how to get rid of these non-copper components effectively. For example:

• A common impurity in copper ores is iron, which gets oxidized and forms iron(II) oxide. This is then combined with silica to form iron silicate, or slag, which separates from the copper and is removed.
• Another important step is the removal of sulfur, achieved by converting sulfides to sulfur dioxide gas, which escapes into the atmosphere.

Filtering out these impurities ensures that the copper acquired is of a high quality and makes the smelting process more efficient. The management of these byproducts is crucial since they might affect environmental sustainability and the efficiency of extraction.