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) \(2 \mathrm{Cu}_{2} \mathrm{~S}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{Cu}_{2} \mathrm{O}+2 \mathrm{SO}_{2}\)

Copper smelting involves a series of chemical reactions that are essential to separate pure copper from its ore. The central part of the smelting process is the reduction reaction, where copper oxide is transformed into copper sulfide. As students explore the intricacies of these reactions, they should focus on understanding the transformation of copper from one compound to another under the influence of heat and a reducing agent.

For instance, the reaction involving the reduction of copper(I) oxide by iron(II) sulfide (\textbf{Cu}\(_2\)O + FeS) results in the formation of copper(I) sulfide and iron(II) oxide. This step is crucial as it leads towards the isolation of copper from its natural impurities. To fully grasp this concept, students are encouraged to visualize the electron exchange taking place in the reduction reaction, where copper loses oxygen and gains sulfide ions.

The smelting of copper requires a reducing agent, which is a substance that donates electrons to another compound in a chemical reaction. In metallurgy, the role of a reducing agent is pivotal for removing oxygen atoms from metal oxides to yield pure metals. In copper smelting specifically, substances like iron(II) sulfide (FeS) act as the reducing agent.

Through the process of reduction, the reducing agent effectively strips oxygen away from copper oxide to help refine copper to a purer state. Students should note that the reducing agent itself gets oxidized in this process, illustrating the fundamental redox principle where for one species to be reduced, another must be oxidized. This concept underscores the interplay of elements in the smeltery and highlights the importance of selecting an appropriate reducing agent for the desired outcome.

Slag is a byproduct of smelting that serves to remove impurities from metal ores. The chemistry behind slag formation involves the reaction between fluxes and non-metallic impurities to form an easily separable layer. One of the common fluxes is silica (SiO\(_2\)), which reacts with impurities like iron(II) oxide (FeO) to create iron silicate (FeSiO\(_3\)) — a type of slag.

Students should understand that this chemical process serves a cleaning purpose. By combining the impurities with the flux, a differentiation occurs between the metal of interest and the undesired components, with the slag floating on top due to its lighter density. This phenomenon emphasizes the significance of slag chemistry in producing pure metals and encourages students to recognize slag as more than just waste but as a crucial player in the refining process.

The reduction of copper compounds during smelting is an essential step towards obtaining elemental copper. It involves the decrease in oxidation state of copper by removing oxygen or sulfur through various chemical reactions, such as the decrease of copper(II) oxide to copper(I) sulfide.

It's vital for students to grasp the concept of oxidation states and their role in metallurgy. Copper's transition through different compounds, each with varying oxidation states, is the pathway to achieving a pure form of this versatile metal. The progression from copper oxides and sulfides down to metal involves a series of carefully controlled reactions, and this understanding of copper's chemical journey forms the backbone of metallurgical science.