Problem 78 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the wrong statements in the following: (a) Chlorofluorocarbons are responsible for ozone layer depletion (b) Green house effect is responsible for global warming. (c) Ozone layer does not permit infrared radiation from the sun to react the earth. (d) Acid rains is mostly because of oxides of nitrogen and sulphur.

Step-by-Step Solution

Answer

Statement (c) is incorrect.

Step 1: Analyze Statement (a)

Statement (a) claims that chlorofluorocarbons (CFCs) are responsible for ozone layer depletion. This is true as CFCs release chlorine atoms in the stratosphere which catalyze the breakdown of ozone molecules. Therefore, this statement is correct.

Step 2: Analyze Statement (b)

Statement (b) suggests that the greenhouse effect is responsible for global warming. The greenhouse effect traps heat in the Earth's atmosphere, contributing to an increase in global temperatures. This statement is correct.

Step 3: Analyze Statement (c)

Statement (c) claims that the ozone layer does not permit infrared radiation from the sun to reach the Earth. This is incorrect because the ozone layer primarily absorbs ultraviolet (UV) radiation, not infrared radiation. Thus, this statement is incorrect.

Step 4: Analyze Statement (d)

Statement (d) states that acid rain is mostly due to oxides of nitrogen and sulfur. These pollutants mix with atmospheric moisture to form acidic compounds, leading to acid rain. This statement is correct.

Key Concepts

Ozone Layer Depletion

The depletion of the ozone layer is primarily due to human-made chemicals, especially chlorofluorocarbons (CFCs). These compounds, once released into the atmosphere, rise to the stratosphere where they are broken down by ultraviolet light. This releases chlorine atoms, which catalyze the destruction of ozone molecules in a chain reaction.

• Ozone is composed of three oxygen atoms and exists primarily in the stratosphere.
• It acts as a protective shield, absorbing most of the sun's harmful ultraviolet (UV) radiation.
• Reduction in this layer results in increased UV exposure on Earth, leading to health issues like skin cancer and cataracts, as well as environmental impacts.

To combat ozone depletion, international efforts such as the Montreal Protocol have been implemented to phase out the use of ozone-depleting substances.

Greenhouse Effect

The greenhouse effect is a natural process that warms the Earth's surface. When the sun’s energy reaches the Earth, some of it is absorbed and re-radiated as infrared energy. Greenhouse gases like carbon dioxide ( CO_2 ), methane ( CH_4 ), and water vapor trap some of this heat in the atmosphere, keeping the planet warm enough to support life. However, human activities have intensified this effect, leading to global warming.

• Fossil fuel burning and deforestation increase CO_2 levels in the atmosphere.
• Methane is released from agriculture, landfills, and other industrial activities.
• The enhanced greenhouse effect is contributing to climate change, causing more extreme weather patterns and rising sea levels.

Preventing the detrimental impacts of global warming involves reducing emissions and increasing energy efficiency.

Acid Rain

Acid rain is a type of precipitation with a lower pH than normal, caused by atmospheric pollution. It forms when sulfur dioxide ( SO_2 ) and nitrogen oxides ( NO_x ) are released into the atmosphere through burning fossil fuels and react with water vapor to form sulfuric and nitric acids.

• These acids fall to the ground, impacting soil, water sources, and plant life.
• It leads to the leaching of essential nutrients from the soil and harms aquatic ecosystems by changing the pH of water bodies.
• Structural materials, especially limestone and marble, are also eroded by acid rain.

To mitigate acid rain, reducing emissions of SO_2 and NO_x through cleaner energy sources and improved regulations is essential.

Infrared and Ultraviolet Radiation

Radiation from the sun comes in various forms, two of which are infrared and ultraviolet (UV) radiation. Infrared radiation has longer wavelengths and is primarily felt as heat. It is crucial for the greenhouse effect as it is the type of energy re-radiated by the Earth.

• Infrared is not blocked by the ozone layer and reaches the Earth's surface, playing a key role in warming the atmosphere.
• In contrast, ultraviolet radiation has shorter wavelengths and is mostly absorbed by the ozone layer.
• UV radiation can lead to skin damage, cataracts, and more if not absorbed effectively by the ozone.

Understanding these radiation types is vital for comprehending their impacts on climate and health.