Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following gases cause pollution when present in the exhaust fumes of vehicles? (a) water vapours (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{CO}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{6}\)

Step-by-Step Solution

Answer

Carbon monoxide (CO) and ethane (C2H6) are pollutants.

Step 1: Identify Harmful Gases

Review the list of gases and determine which are known to contribute to air pollution. Typically, nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons like ethane (C2H6) are pollutants. Water vapor is not considered a pollutant, and CO2, although a greenhouse gas, is not directly harmful to health like CO.

Step 2: Analyze Each Gas

- **Water vapors ( 4a)**: Generally not harmful as they are natural. - **Carbon dioxide ( 4b)**: While a greenhouse gas, it is not considered a pollutant in the same way volatile organic compounds or CO is. - **Carbon monoxide ( 4c)**: A toxic pollutant that can replace oxygen in the blood. - **Ethane ( 4d)**: Contributes to secondary pollutants like ozone, therefore pollution-causing.

Step 3: Choose the Pollutants

From the analysis, select the gases that are recognized as pollutants in vehicle exhaust: carbon monoxide ( 4c) and ethane ( 4d). These contribute to air pollution and pose health risks.

Key Concepts

Vehicle Exhaust

When vehicles burn fuel, they produce exhaust fumes as a byproduct. These fumes consist of several gases, each with its own impact on the environment and human health. Exhaust is unavoidable in vehicles with combustion engines, but understanding what it contains is key to tackling the pollution problem.

Typically, vehicle exhaust comprises byproducts like

• nitrogen oxides (NOx)
• carbon monoxide (CO)
• hydrocarbons
• carbon dioxide (CO₂)
• water vapor

While some components, like water vapor, are harmless, others are pollutants. Thus, analyzing vehicle exhaust is crucial to reduce air pollution.

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas that is highly toxic. It's mainly produced from the incomplete combustion of carbon-containing fuels, like gasoline in car engines. Because it lacks color and smell, it can be a silent threat, leading to serious health effects.

The danger of carbon monoxide lies in its ability to bind with hemoglobin in human blood, replacing oxygen. This can cause dizziness, confusion, or even suffocation at high levels. Effective measures to lower CO emissions include:

• Improving fuel combustion efficiency
• Using catalytic converters
• Promoting the use of cleaner energy sources

Greenhouse Gases

Greenhouse gases refer to gases that trap heat in the atmosphere, contributing to global warming. Carbon dioxide ( CO₂) is one of the most common greenhouse gases emitted by vehicles. Despite not being directly toxic like CO, it plays a significant role in climate change.

Greenhouse gases from vehicles stem from the burning of fossil fuels, making transportation a significant source of global CO₂ emissions. To mitigate these emissions:

• Enhance fuel efficiency
• Shift to electric or hybrid vehicles
• Implement stricter emissions standards

Recognizing the impact of greenhouse gases is vital for environmental policies and climate change strategies.

Ethane Pollution

Ethane ( C₂H₆) is a hydrocarbon often found in vehicle emissions. It's not as widely known as other pollutants but contributes significantly to secondary pollution. When ethane interacts with sunlight and other chemicals, it forms ground-level ozone, part of the harmful smog we see in urban areas.

Ground-level ozone can cause respiratory problems and damage crops, while also impacting climate patterns. Addressing ethane emissions involves:

• Reducing motor vehicle usage
• Enhancing fuel quality
• Promoting alternative fuels with lower hydrocarbon content

Understanding ethane's role in pollution helps to devise better air quality management strategies.