Question

Ozone in stratosphere is depleted by (a) \(\mathrm{C}_{7} \mathrm{~F}_{16}\) (b) \(\mathrm{C}_{6} \mathrm{~F}_{6}\) (c) \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{Cl}_{6}\)

Short answer

The correct answer is (c) \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\).

Step-by-step solution

Understanding the Question

The question asks us to identify which chemical compound is responsible for depleting ozone in the stratosphere. The depletion is commonly associated with compounds known as CFCs (Chlorofluorocarbons). By evaluating the given options, we need to determine which is a CFC.

Identifying the Chemical in Question

Examine the chemical formulas provided: 1. \(\mathrm{C}_{7} \mathrm{~F}_{16}\) is a perfluorinated compound (fully fluorinated without chlorine). 2. \(\mathrm{C}_{6} \mathrm{~F}_{6}\) is also fully fluorinated, known as hexafluorobenzene, without any chlorine.3. \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) contains carbon, chlorine, and fluorine, and is known as dichlorodifluoromethane, a type of CFC.4. \(\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{Cl}_{6}\), also known as hexachlorocyclohexane, is a chlorinated hydrocarbon used in pesticides.The compound \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) matches the description of CFCs, which are known to deplete ozone.

Selecting the Correct Answer

Considering the identified properties, \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) (dichlorodifluoromethane) is the compound that is a CFC and known to contribute to stratospheric ozone depletion. Therefore, the correct answer is option (c).

Key concepts

Stratosphere Chemistry

The stratosphere is the second major layer of Earth's atmosphere, lying above the troposphere and beneath the mesosphere. A defining characteristic of the stratosphere is the presence of ozone, a molecule consisting of three oxygen atoms (O₃). This region is critical for life on Earth as it absorbs the majority of the Sun's harmful ultraviolet (UV) radiation. Without it, the surface of our planet would be exposed to increased levels of UV radiation, leading to severe consequences for both human health and the environment.
The chemistry of the stratosphere is unique due to the interactions between various gases and the intense UV radiation. Ozone is naturally created and destroyed in a continuous cycle in the stratosphere, maintaining a balance that protects life on Earth. However, human activities have introduced compounds that disrupt this balance, leading to ozone depletion.
The depletion occurs due to reactions that break down ozone molecules, thinning the ozone layer, and allowing more UV radiation to reach the Earth. Understanding these chemical processes is crucial for developing strategies to protect the ozone layer and, by extension, life on Earth.

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are a class of chemical compounds that include carbon, chlorine, and fluorine. They were once widely used in applications such as refrigerants, propellants in aerosol sprays, and as solvents for cleaning electronic equipment. However, these compounds have been found to have a detrimental effect on the ozone layer.
CFCs are stable in the lower atmosphere but once they reach the stratosphere, they are broken down by UV radiation. This breakdown releases chlorine atoms, which then react with ozone molecules, resulting in their depletion. The reaction can be simplified as follows:

• Chlorine from CFCs reacts with ozone (O₃) to form chlorine monoxide (ClO) and oxygen (O₂).
• The ClO can then react with a free oxygen atom to regenerate a chlorine atom and produce more O₂.

This cycle can repeat thousands of times, allowing a single chlorine atom to destroy a large number of ozone molecules. Because of these harmful effects, the use of CFCs has been largely phased out under international agreements like the Montreal Protocol.

Environmental Chemistry

Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It's an interdisciplinary field that involves the study of the sources, reactions, transport, effects, and fates of chemical species in the air, water, and soil environments. One of its critical areas of study is understanding the impact of human activity on the natural environment.
In the context of ozone depletion, environmental chemistry focuses on the substances introduced by human actions, such as CFCs, and their effects on the stratospheric ozone. Through this lens, scientists have been able to identify the chemical pathways leading to ozone depletion and ascertain the extent of damage caused by these compounds.
This knowledge is vital for creating effective environmental policies and technologies aimed at reducing or eliminating the emission of harmful chemicals. Environmental chemistry serves as a bridge between scientific research and practical solutions, ensuring the sustainability and health of our planet by promoting practices that minimize pollution and preserve critical natural processes like the protection provided by the ozone layer.