Two ores of the same metal \((\mathrm{M})\) are \(\left(\mathrm{A}_{1}\right)\) and \(\left(\mathrm{A}_{2}\right.\) ). (1) \(\mathrm{A}_{1} \stackrel{\text { calcination }}{\rightarrow}\) Black residue \(\mathrm{C}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\) (2) \(\mathrm{A}_{1} \stackrel{\mathrm{HCl}_{2} \mathrm{Kl}}{\longrightarrow} \mathrm{I}_{2}+\mathrm{D}\) precipitate (3) \(\mathrm{A}_{2} \stackrel{\text { roasting }}{\longrightarrow}\) Gas (G) \(+\) Metal \((\mathrm{M})\) (4) \(\mathrm{G} \frac{+\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} \text { acidified }}{\longrightarrow}\) Green solution Identify \(\mathrm{A}_{1}\) and \(\mathrm{A}_{2}\) here? (a) \(\mathrm{A}_{1}=\mathrm{CuCO}_{3} \cdot \mathrm{Cu}(\mathrm{OH})_{2}, \mathrm{~A}_{2}=\mathrm{Cu}_{2} \mathrm{~S}\) (b) \(\mathrm{A}_{1}=\mathrm{Cu}_{2} \mathrm{~S}, \mathrm{~A}_{2}=\mathrm{CuCO}_{3} \cdot \mathrm{Cu}(\mathrm{OH})_{2}\) (c) \(\mathrm{A}_{1}=\mathrm{CuFeS}_{2}, \mathrm{~A}_{2}=\mathrm{Cu}_{2} \mathrm{~S}\) (d) None of these

Metallurgy is the branch of science and technology that focuses on the extraction and processing of metals from their ores. The field encompasses a series of steps which include mining the ore, followed by separation of the metal from its impurities and altering its physical and chemical properties to suit desired applications. It fundamentally includes processes such as calcination, roasting, smelting, refining, and alloying.

In the production of metals, metallurgy involves chemical reactions which are vital in isolating the metal in a usable form. The two processes, calcination and roasting, are essential in extracting metals from their ores. Calcination typically refers to the heating of carbonate and hydroxide ores in the absence of air to remove volatile substances and convert the ore into its oxide. Roasting involves heating sulfide ores in the presence of an excess of air which leads to the formation of oxides and the release of sulfur dioxide gas.

These processes are critical initial steps in the chain of metallurgical procedures needed to convert a raw mineral deposit into a purer metallic form for industrial use.

Sulfide ores are one of the most common types of ores mined for the extraction of various metals. These ores contain metal sulfides where a metal is bonded to sulfur atoms. In the context of the textbook exercise, we analyze an ore labeled A2, which is identified as a sulfide ore based on its chemical behavior during roasting. Roasting this type of ore typically releases sulfur dioxide, a gas with a characteristic burning smell.

For example, in extracting copper from its sulfide ore, heat and air are applied in a process called roasting, where the copper sulfide is converted into liquid copper and sulfur dioxide gas. This conversion is critical, as it facilitates the separation of copper from sulfur and prepares the metal for further refinement and purification processes. Understanding the properties of sulfide ores and their reaction patterns during roasting is a fundamental aspect of metallurgical chemistry.

Carbonate ores contain metal ions in combination with the carbonate ion (CO3^2-). Metallurgists usually process these types of ores through calcination, which involves heating the ore at high temperatures in the absence of oxygen. This causes the carbonate to decompose into an oxide and carbon dioxide gas. For instance, in the exercise, A1 is suspected to be a carbonate ore because of its decomposition into CO2 and H2O, indicating the presence of both carbonate and hydroxide groups.

The decomposition reaction for a basic copper carbonate like CuCO3.Cu(OH)2, when subjected to calcination, provides vital clues to its identity: the evolution of water suggests the loss of hydroxide as water vapor, while the release of carbon dioxide points to the breakdown of the carbonate group. This thermal decomposition is an important step as it simplifies the ore to a more reactive form, which is easier to further process in the extraction of the metal.

Chemical reactions are the backbone of metallurgical processes, and they must be thoroughly understood to ensure the successful extraction and refinement of metals from their ores. Both calcination and roasting involve thermal decomposition reactions, which can be visually monitored through the change in color or state of the ore, and chemically confirmed by the products they release, such as gases like CO2 and SO2.

In the given exercise, copper carbonate hydroxide (CuCO3.Cu(OH)2) undergoes calcination, resulting in a black residue, carbon dioxide, and water. This indicates the chemical reaction of a carbonate ore decomposing into oxide and releasing CO2 and H2O. The sulfide ore Cu2S, when roasted, turns into copper (the metal) and sulfur dioxide. The greenhouse gas G, upon reaction with an oxidizing agent like potassium dichromate (K2Cr2O7), forms a green solution due to the reduction of Cr6+ to Cr3+, further confirming SO2 as the resulting gas. These reactions illustrate the reliance of metallurgy on chemical principles to derive metals from their natural state within the Earth's crust.