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

Question

Which of the following is produced when conce trated 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

(a) Hg is produced when cinnabar is roasted in excess air.

Step 1: Understanding the Chemical Process

Roasting cinnabar (HgS) in excess air involves heating it in the presence of oxygen. Cinnabar is primarily composed of mercury(II) sulfide (HgS), and when it is roasted, a chemical reaction occurs where mercury sulfide reacts with oxygen to produce mercury metal (Hg) and sulfur dioxide (SO2). The reaction for this process is:\[\text{HgS} + \text{O}_2 \rightarrow \text{Hg} + \text{SO}_2\]

Step 2: Identifying the Final Product

The chemical reaction from the roasting of cinnabar in excess air shows that mercury metal (Hg) is produced as one of the products. Sulfur dioxide (SO2) is the other product, but since we're interested in the elemental final products when cinnabar is roasted, we focus on Hg.

Step 3: Selecting the Correct Answer

From the given options, we need to select the element that is produced when cinnabar is roasted. Based on the chemical reaction, mercury (Hg) is the element produced. The correct option from the choices provided (a, b, c, d) is (a) Hg.

Key Concepts

Chemical Reaction of Roasting Cinnabar

When we talk about roasting cinnabar, we're diving into the world of chemical reactions. A chemical reaction is a process where substances, known as reactants, are transformed into different substances, or products. In the case of cinnabar (HgS), it consists primarily of mercury sulfide. When cinnabar is roasted, it is heated in the presence of oxygen (O₂). This is a critical part as oxygen is needed to facilitate the transformation.- **Reactants in this process:** - Mercury sulfide (HgS) - Oxygen (O₂) - **Products of this reaction:** - Mercury (Hg) - Sulfur dioxide (SO₂)The chemical equation for this reaction is:\[ \text{HgS} + \text{O}_2 \rightarrow \text{Hg} + \text{SO}_2 \]This equation shows us that mercury sulfide reacts with oxygen gas to produce mercury and sulfur dioxide. Understanding chemical reactions like this one helps us predict the outcome of roasting cinnabar, such as the formation of mercury and sulfur dioxide.

Mercury Production During Roasting

Mercury production through roasting cinnabar is a fascinating process. By heating cinnabar with air, we isolate mercury, an element known for its unique properties and historical significance. - **Physical Properties of Mercury:** - It is the only metal that is liquid at room temperature. - Has a shiny, silver appearance. - **Production Process:** - Begins with heating cinnabar (HgS) in the presence of oxygen. - During this process, mercury sulfide decomposes into mercury vapor and sulfur dioxide gas. As the reaction proceeds, mercury vapor is released and subsequently condensed to form liquid mercury. This process has been historically significant in various applications, from thermometers to dental amalgams, although its use has declined over health concerns.

Role and Impact of Sulfur Dioxide

Sulfur dioxide (SO₂) is the other product of roasting cinnabar, and it serves a crucial role in the chemical reaction. - **Formation of Sulfur Dioxide:** - Arises from the oxidation of sulfide ions (S²⁻) in cinnabar when they react with oxygen. - Result of the same chemical reaction that produces mercury. - **Environmental and Health Impact:** - Sulfur dioxide is a pungent gas that can affect human health. - It is a significant air pollutant contributing to acid rain. This makes handling and disposal a concern in industrial practices, urging us towards more eco-friendly technologies and regulations. Despite its nuisance as a pollutant, sulfur dioxide is used in the food and wine industry as a preservative, showcasing its versatility.