Problem 27 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Extraction of zinc from zinc blende is achieved by. (a) electrolytic reduction (b) roasting followed by reduction with carbon (c) roasting followed by reduction with another metal (d) roasting followed by self-reduction

Step-by-Step Solution

Answer

(b) roasting followed by reduction with carbon

Step 1: Understand the Ore

Zinc blende is primarily composed of zinc sulfide (ZnS). Understanding the composition of the ore helps in identifying the suitable extraction method.

Step 2: Roasting Process

In the roasting process, zinc sulfide reacts with oxygen to form zinc oxide and sulfur dioxide. The chemical reaction is: \[ 2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2 \] This step is essential in converting zinc sulfide to zinc oxide, which can be reduced easily.

Step 3: Reduction Process

After roasting, zinc oxide needs to be reduced to extract pure zinc. This is typically done using carbon, where zinc oxide reacts with carbon to form zinc and carbon monoxide: \[ ZnO + C \rightarrow Zn + CO \] This process is known as carbon reduction and is commonly used for converting zinc oxide to zinc.

Step 4: Conclusion

The extraction of zinc from its ore, zinc blende, involves roasting followed by reduction with carbon. This makes option (b) the correct choice.

Key Concepts

Roasting Process

Zinc extraction begins with the roasting of zinc blende, which is primarily zinc sulfide (ZnS). During the roasting process, zinc sulfide is converted to zinc oxide. This process is crucial for preparing the ore for further reduction. The key reaction taking place is: \[ 2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2 \]Roasting involves heating the ore in the presence of sufficient oxygen. This results in the oxidation of zinc sulfide to zinc oxide, and it also releases sulfur dioxide gas. The transformation of zinc sulfide into zinc oxide is necessary because zinc oxide can be more readily reduced to metallic zinc.

• Roasting helps remove sulfur impurities.
• This step also increases the concentration of zinc in the ore.
• The process takes place at temperatures that are high enough to cause the desired reactions.

By converting ZnS to ZnO, we create a metal oxide form that is easier to reduce, paving the way for the extraction of pure zinc.

Reduction Process

After the roasting process has successfully converted zinc sulfide into zinc oxide, the next critical phase is the reduction process. The primary objective of this step is to extract metallic zinc by reducing zinc oxide using carbon, commonly in the form of coke. The chemical reaction involved is straightforward:\[ ZnO + C \rightarrow Zn + CO \]Here, carbon acts as a reducing agent. It donates electrons to the zinc oxide, transforming it into metallic zinc and carbon monoxide. This process, commonly known as carbon reduction, is performed at high temperatures to ensure proper conversion.

• Carbon reduction is a widely used method due to its effectiveness with zinc oxide.
• The production of carbon monoxide as a byproduct makes it essential to manage emissions.
• This step results in pure zinc, which can then be further refined if necessary.

With successful reduction, the zinc extracted is ready for industrial use or further purification processes. The efficiency of this step is crucial for obtaining high yields of zinc from the ore.

Zinc Blende

Zinc blende, also known scientifically as sphalerite, is the primary ore from which zinc is extracted. Its chief component is zinc sulfide (ZnS), a compound that provides a significant source of zinc metal through its processing. Understanding the properties of zinc blende is vital for efficient extraction:

• Zinc blende often contains other minerals such as iron, cadmium, and lead sulfide.
• The presence of these impurities can affect the processing and extraction stages.
• Efficient concentration techniques are needed to increase the purity of zinc blende before processing.

The processing begins with physical methods to upgrade the ore concentration, followed by chemical treatment through roasting and reduction to extract the zinc metal effectively. The identification and preparation of zinc blende set the stage for the successful recovery of zinc, ensuring that the subsequent chemical processes yield optimal results.