Problem 22 - A Complete Resource Book in Chemistry for JEE Main

Question

In the extraction of zinc, the formation of blue flame is due to the burning of (a) \(\mathrm{C}\) (b) \(\mathrm{CO}\) (c) \(\mathrm{Zn}\) (d) \(\mathrm{ZnO}\)

Step-by-Step Solution

Answer

The blue flame is due to the burning of CO.

Step 1: Understanding the Reaction

In the extraction of zinc from its ore, zinc oxide is reduced using carbon monoxide. During this process, different chemical reactions occur that involve carbon-based substances and zinc compounds. We must identify the reaction responsible for a blue flame.

Step 2: Examining Reaction Products

The main reaction involves the reduction of zinc oxide ( ZnO) with carbon monoxide ( CO) to produce zinc ( Zn) and carbon dioxide ( CO_2). However, when determining the cause of the blue flame, we need to consider any additional reactions or burning processes.

Step 3: Identifying the Source of Flame Color

Blue flames are typically associated with the burning of carbon monoxide (CO). When carbon monoxide burns in the presence of oxygen, it produces carbon dioxide and emits a blue flame: \[2 \, ext{CO} + ext{O}_2 ightarrow 2 \, ext{CO}_2\] Thus, the burning of CO is responsible for the blue flame observed during the zinc extraction process.

Key Concepts

Chemical Reactions in Metallurgy

In the field of metallurgy, chemical reactions play a crucial role in extracting metals from their ores. For zinc extraction, these reactions help convert zinc oxide (ZnO) into pure zinc metal. This conversion involves a series of steps that modify the compound’s chemical structure. Most metal extraction processes begin with creating a "concentrate" from the ore, which then undergoes reduction reactions to obtain the metal.

During these reactions, reducing agents such as carbon or carbon-based compounds are introduced to remove oxygen or other impurities. Reactions may include combinations of oxidation and reduction, which are essential for breaking down the metal compounds into elemental forms. Through systematic chemical transformations, the desired metal is separated from other components, achieving a high level of purity.

Zinc Oxide Reduction

The reduction of zinc oxide is a critical step in zinc extraction. Zinc oxide reduction involves removing oxygen from ZnO to form elemental zinc. This is typically achieved by using carbon monoxide (CO) as a reducing agent. The chemistry here is clear:

• A redox reaction takes place where CO acts as the reducer and ZnO undergoes reduction.
• The chemical equation involved is: \[ ext{ZnO} + ext{CO} \rightarrow ext{Zn} + ext{CO}_2\]
• This reaction effectively removes the oxygen from zinc oxide and produces zinc metal.

The reduction reaction takes place in a furnace at elevated temperatures to drive the reaction forward. The end product, zinc, is then collected, while carbon dioxide, a byproduct, is released into the atmosphere.

Temperature control is essential since higher temperatures increase the reaction rate and improve zinc yield. Consequently, this process is optimized to ensure efficient zinc recovery.

Combustion Reactions

During metal extraction processes like zinc extraction, combustion reactions play a vital role. These reactions are chemical processes where a fuel, such as carbon monoxide ( ext{CO}), reacts with oxygen to release energy. One observable result of this reaction type is flame production.

• Combustion reactions are exothermic, meaning they release energy in the form of heat and light.
• The combustion of carbon monoxide in the presence of oxygen is described by:\[2 \, ext{CO} + ext{O}_2 \rightarrow 2 \, ext{CO}_2\]
• This particular reaction results in the characteristic blue flame noticed during the zinc extraction process.

Metallurgical processes often rely on the heat from combustion reactions. Not only does this heat facilitate reduction reactions, but it also helps maintain the necessary operational temperatures within industrial furnaces.

Combustion reactions thereby support both the practical elements of extracting metals and contribute visually, often indicating that a specific reaction is occurring successfully.