Problem 73 - A Complete Resource Book in Chemistry for JEE Main

Question

Use of chlorofluoro carbons is not encouraged because (a) they are harmful to the eyes of people that use it (b) they damage the refrigerators and air conditioners (c) they eat away the ozone in the atmosphere (d) they destroy the oxygen layer

Step-by-Step Solution

Answer

CFCs eat away the ozone layer, so option (c) is correct.

Step 1: Understanding Chlorofluorocarbons

Chlorofluorocarbons (CFCs) are compounds made of carbon, chlorine, and fluorine. They were commonly used in refrigeration, air conditioning, and aerosol propellants.

Step 2: Investigating Environmental Impact

The main concern with chlorofluorocarbons is their ability to rise into the stratosphere after being released. Once in the atmosphere, CFCs break down under ultraviolet radiation, releasing chlorine atoms.

Step 3: Linking CFCs to the Ozone Layer

Chlorine atoms released from the breakdown of CFCs react with ozone (O_3), causing depletion of the ozone layer. This thins the protective ozone layer, allowing more harmful ultraviolet radiation to reach Earth's surface.

Step 4: Evaluating Provided Options

Analyzing each option: (a) CFCs are not directly harmful to human eyesight. (b) CFCs do not damage refrigerators and air conditioners but were used as refrigerants. (c) CFCs have a known impact on the ozone layer by contributing to its depletion. (d) There is no 'oxygen layer' as such to protect; oxygen exists as a part of the atmosphere but is not destroyed by CFCs.

Step 5: Selecting the Correct Answer

Based on the investigation, the correct reason for not encouraging CFC use is because they cause damage to the ozone layer. Therefore, the answer is (c) they eat away the ozone in the atmosphere.

Key Concepts

Chlorofluorocarbons

Chlorofluorocarbons, often abbreviated to CFCs, are synthetic compounds composed primarily of chlorine, fluorine, and carbon. In the past, these compounds were widely used in everyday products, due to their stable, non-flammable, and non-toxic characteristics, which made them ideal for applications such as:

• Refrigeration and air conditioning as coolants.
• Aerosol propellants in spray cans.
• Foaming agents in insulation and packaging.

Despite these beneficial uses, CFCs have a dark side. One of their most significant drawbacks is their long lifespan. This allows them to eventually reach the upper levels of the atmosphere, where they begin to cause problems for the environment.

Ultraviolet Radiation

Ultraviolet (UV) radiation is a form of electromagnetic radiation that comes naturally from the sun. Although invisible to the naked eye, it plays an essential role in various earth processes, such as vitamin D synthesis in humans. However, excessive UV exposure can harm living organisms by:

• Damaging skin cells, which can lead to skin cancer.
• Affecting plant growth and photosynthesis.
• Causing eye damage, such as cataracts.

The Earth's ozone layer is a shield that absorbs the majority of harmful UV radiation. This protection is crucial for maintaining safe levels of UV radiation on our planet's surface, preventing widespread biological damage.

Environmental Impact

The environmental impact of chlorofluorocarbons extends primarily to their interaction with the ozone layer. Once CFCs ascend to the stratosphere, they undergo a chemical breakdown resulting in the release of chlorine molecules. These chlorine atoms are highly reactive and engage in a destructive cycle with ozone molecules:

• Chlorine atoms react with ozone ( O_3 ), breaking it down into oxygen ( O_2 ).
• This depletion allows more UV radiation to penetrate through the atmosphere.

The ozone layer acts as Earth's sunscreen by absorbing damaging UV rays, so its depletion poses significant risks, such as increased rates of skin cancer, genetic damage in living cells, and consequently influencing ecosystems adversely. The declining condition of the ozone layer sparked international agreement, such as the Montreal Protocol, to phase out substances that are responsible for ozone depletion, thereby marking a significant stride in global environmental protection efforts.