Problem 89 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is produced when concentrated cinnabar is roasted in the excess of air? (a) \(\mathrm{Hg}\) (b) \(\mathrm{Fe}\) (c) \(\mathrm{Zn}\) (d) \(\mathrm{Al}\)

Step-by-Step Solution

Answer

When cinnabar is roasted, it produces Hg (mercury).

Step 1: Understanding Cinnabar

Cinnabar is a mineral that consists of mercury sulfide, with the chemical formula \( \text{HgS} \). It is the primary ore from which mercury is extracted.

Step 2: The Roasting Process

Roasting is a metallurgical process involving the heating of ore in the presence of excess air or oxygen. For cinnabar, the primary chemical reaction during roasting is \( \text{HgS} + \text{O}_2 \rightarrow \text{Hg} + \text{SO}_2 \). This means cinnabar is converted into mercury (\( \text{Hg} \)) and sulfur dioxide (\( \text{SO}_2 \)).

Step 3: Identifying the Product

From the roasting reaction of cinnabar, we can see that mercury (\( \text{Hg} \)) is the main product. The sulfur from \( \text{HgS} \) combines with oxygen to form \( \text{SO}_2 \).

Key Concepts

Cinnabar

Cinnabar is a fascinating mineral and is the most significant ore of mercury. Its composition is primarily mercury sulfide (\( \text{HgS} \)). This rich red mineral has been used since ancient times, not just for mercury extraction, but also as a pigment due to its vibrant color.
As the chief source of mercury, cinnabar's presence in a region often signifies the mining and industrial use of this element. Mercury itself is a heavy, silver metal that is liquid at room temperature, making it unique compared to other metals found in ores.

• The chemical formula for cinnabar is \( \text{HgS} \).
• It predominantly appears in a bright red crystalline form.
• Cinnabar deposits are often found around volcanic regions and hot springs.

Understanding cinnabar is key to discussions about mercury in metallurgy and various industries.

Mercury Extraction

The main method to extract mercury from cinnabar is through a process called roasting. Roasting involves heating the ore in the presence of air. This is a crucial step in separating mercury from its sulfide ore. The reaction that occurs during this process is:
\[ \text{HgS} + \text{O}_2 \rightarrow \text{Hg} + \text{SO}_2 \]
This reaction highlights that the heating of cinnabar leads to the release of mercury (\( \text{Hg} \)) and the conversion of sulfur (\( \text{S} \)) into sulfur dioxide (\( \text{SO}_2 \)). This is not just a simple heating process; it involves careful control of heat and air supply.

• Roasting is usually performed at temperatures around 500-600°C.
• The process is conducted in a controlled environment to capture mercury vapor.
• Mercury is distilled in this process, ensuring high purity of the output.

Understanding this extraction process is essential for the production of mercury and emphasizes the caution needed due to the toxicity of mercury.

Chemical Reactions in Metallurgy

In metallurgy, chemical reactions are pivotal in extracting and refining metals from their ores. The roasting of cinnabar is an excellent example of these chemical transformations. Roasting involves turning sulfide ores into oxides, which are easier to reduce to pure metal. In the case of cinnabar, the reaction is an oxidation-reduction process where mercury sulfide reacts with oxygen.
Key aspects of such reactions in metallurgy include:

• Heat is often used to drive these reactions forward.
• The presence of oxygen is critical for the success of processes like roasting.
• The products of these reactions often include gaseous byproducts like \( \text{SO}_2 \), which need proper handling due to environmental concerns.

These reactions are crucial for the purification of metals and often involve intricate setups to ensure safety and efficiency. Recognizing the balance between extracting valuable metals and minimizing environmental impact is a core concern in modern metallurgy.