Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

Taj Mahal is threatened due to the effect of (a) hydrogen (b) oxygen (c) chlorine (d) sulphur dioxide

Step-by-Step Solution

Answer

The Taj Mahal is threatened by sulphur dioxide.

Step 1: Identify the Problem Substance

The Taj Mahal, made of white marble, is threatened by substances causing pollution and deterioration. We need to identify which substance from the given options actually affects the structure.

Step 2: Understand Marble Corrosion

The primary cause of damage to marble is acidic substances. When certain gases in the air react with rainwater, they form acids, leading to acid rain. Acid rain dissolves calcium carbonate (the main component of marble) and causes deterioration.

Step 3: Analyze Each Option

- (a) Hydrogen is not an acidifying agent and does not contribute to acid rain. - (b) Oxygen is a natural part of the air and doesn't form dangerous acids with water. - (c) Chlorine is involved in the formation of chlorine-containing compounds but is not the main component of acid rain. - (d) Sulphur dioxide combines with water to form sulfurous acid, which further oxidizes to sulfuric acid. This is a major contributor to acid rain which harms the marble structure.

Step 4: Determine the Correct Answer Based on Options

Given the analysis of each option, sulphur dioxide is the gas that reacts with water to form acids, which leads to the deterioration of marble. Therefore, "sulphur dioxide" is the correct answer.

Key Concepts

Marble Corrosion

Marble, a beautiful and durable natural stone, is often used for sculptures and buildings, like the Taj Mahal. However, marble is vulnerable to corrosion, primarily due to its composition of calcium carbonate. When marble is exposed to acidic substances, it can undergo chemical reactions that deteriorate its surface. This process is known as marble corrosion.

Acid rain is one of the leading causes of marble corrosion. It occurs when rainwater interacts with gases like sulphur dioxide and nitrogen oxides in the atmosphere, forming weak acids. These acids can react with the calcium carbonate in marble, leading to its gradual decay.

Some signs of marble corrosion include pitting, discoloration, and surface roughness. Over time, this damage can lead to a loss of intricate details and overall weakening of the structure. Understanding these effects helps in adopting protective measures, such as using coatings or reducing air pollution sources, to preserve valuable marble structures.

Sulphur Dioxide

Sulphur dioxide (SO2) is a significant pollutant that plays a central role in the formation of acid rain. It is a colorless gas with a pungent smell, and it primarily comes from burning fossil fuels like coal and oil. Industrial processes, such as metal smelting and vehicle emissions, also contribute to the release of sulphur dioxide into the atmosphere.

When sulphur dioxide enters the atmosphere, it can react with water vapor and oxygen, forming sulfurous acid ( SO_2 + H_2O ightarrow H_2SO_3 ). This acid can further oxidize to form sulfuric acid ( H_2SO_3 + 1/2 O_2 ightarrow H_2SO_4 ), a strong acid that contributes to acid rain.

Acid rain, as mentioned, is particularly harmful to marble and other carbonate-bearing materials. It can also damage metals, cause paint to peel, and harm vegetation. The environmental and structural impacts of sulphur dioxide make it an important substance to monitor and manage in efforts to reduce air pollution.

Air Pollution Effects on Structures

Air pollution has far-reaching effects on various materials and structures. Pollutants like sulphur dioxide, nitrogen oxides, and particulate matter can severely impact buildings, monuments, and infrastructure.

Here are some common effects of air pollution on structures:

• Corrosion: Acid rain resulting from air pollutants accelerates the corrosion of metals and stone materials. This can lead to structural vulnerabilities and safety concerns.
• Discoloration: Pollutants cause the surfaces of buildings to become dirty and discolored, often resulting in a need for more frequent cleaning and maintenance.
• Degradation: Materials like limestone and marble lose their finish and details over time, as seen in numerous historic monuments worldwide.
• Increased Maintenance Costs: The damage from air pollutants necessitates regular upkeep, restoration, and protective measures, increasing maintenance expenses.

Reducing air pollution through policy changes, alternative energy sources, and innovative technology can help mitigate these effects and preserve structural integrity for future generations.