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) \(\bar{C}\) (b) \(\mathrm{CO}\) (c) \(\mathrm{Zn}\) (d) \(\mathrm{ZnO}\)

Step-by-Step Solution

Answer

The formation of blue flame is due to the burning of carbon monoxide (\(\mathrm{CO}\)).

Step 1: Analyze the Question

The question asks for the cause of the blue flame during zinc extraction. Various substances in the process, such as carbon (\(\bar{C}\)), carbon monoxide (\(\mathrm{CO}\)), zinc (\(\mathrm{Zn}\)), and zinc oxide (\(\mathrm{ZnO}\)), can potentially cause a flame.

Step 2: Identify Relevant Chemical Reactions

In the extraction of zinc, particularly by the reduction of zinc oxide (\(\mathrm{ZnO}\)) using carbon, carbon monoxide (\(\mathrm{CO}\)) is produced as a byproduct. \(\mathrm{CO}\) is known to burn with a blue flame.

Step 3: Evaluate the Options

Among the given options, zinc (\(\mathrm{Zn}\)), zinc oxide (\(\mathrm{ZnO}\)), carbon (\(\bar{C}\)), and carbon monoxide (\(\mathrm{CO}\)), the substance known to produce a blue flame when it burns is carbon monoxide (\(\mathrm{CO}\)).

Step 4: Choose the Correct Answer

Based on the analysis in previous steps, carbon monoxide (\(\mathrm{CO}\)) is the substance responsible for the blue flame observed during the extraction of zinc.

Key Concepts

Blue Flame

A blue flame is an important visual indicator in many chemical processes, including the extraction of zinc. The color of a flame can tell us a lot about the chemical reactions taking place. Flame Color Characteristics
- Blue flames are often associated with the combustion of gases. - This color indicates a complete combustion process, meaning there is enough oxygen available to allow for the efficient burning of the fuel. - In a blue flame, most of the energy is in the form of heat rather than light, due to the complete combustion. Relevance in Zinc Extraction
During zinc extraction, the appearance of a blue flame is particularly related to the burning of carbon monoxide ()CO). This indicates that the carbon monoxide is reacting with oxygen to form carbon dioxide, releasing energy in the form of heat and light, which results in the blue coloration of the flame.

Carbon Monoxide

Carbon monoxide (CO) plays a significant role in the extractive metallurgy of zinc. It is a byproduct of the reduction processes and an essential indicator of complete combustion. Formation and Properties
- Carbon monoxide is produced when carbon is used to reduce zinc oxide (ZnO). - It is a colorless, odorless gas that is less dense than air and burns with a characteristic blue flame. Function in Zinc Extraction
- In the zinc extraction process, carbon monoxide aids in reducing zinc oxide, facilitating the release of zinc metal. - The combustion of CO to form carbon dioxide is an exothermic reaction. This means it releases heat, which is crucial in maintaining the high temperatures needed for the extraction process. Carbon monoxide's ability to produce a blue flame is directly utilized in metallurgical procedures by indicating complete combustion and efficient heat production.

Zinc Oxide Reduction

The reduction of zinc oxide (ZnO) is a key reaction in zinc metal production. It involves transforming zinc oxide into zinc through a series of chemical reactions.Reduction Process
- Zinc oxide has to be reduced to zinc metal, a process typically achieved using carbon as the reducing agent.- The carbon combines with the oxygen in zinc oxide, forming carbon monoxide and liberating pure zinc.The reaction can be simplified as:\[ \text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO} \]Importance of This Reaction
- The zinc oxide reduction is crucial because it changes the zinc from its oxide form to a metallic form, which is commercially valuable. - The generation of carbon monoxide during this process also plays a secondary role as it combusts in the presence of oxygen, producing additional heat (and the characteristic blue flame) required for the process to be sustainable at high temperatures.