Question

Because of increasing evidence of damage to the ozone layer, chloroflu- orocarbon \((\mathrm{CFC})\) production was banned in \(1996 .\) However, there areabout 100 million auto air conditioners in operation that still use CFC-12 \(\left(\mathrm{CF}_{2} \mathrm{Cl}_{2}\right) .\) These air conditioners are recharged from stockpiled supplies of \(\mathrm{CF} \mathrm{C}-12 .\) If each of the 100 million automobiles contains 1.1 \(\mathrm{kg}\) of \(\mathrm{CFC}-12\) and leaks 25\(\%\) of its \(\mathrm{CFC}-12\) into the atmosphere per year, how much chlorine, in \(\mathrm{kg}\) , is added to the atmosphere each year due to auto air conditioners? (Assume two significant figures in your calculations.)

Short answer

Total mass of chlorine released to the atmosphere from auto air conditioners annually is approximately \(2.8 \times 10^7\) kg.

Step-by-step solution

Calculate the annual CFC-12 leakage

First, determine the total amount of CFC-12 that leaks annually from all 100 million auto air conditioners. To do this, multiply the amount of CFC-12 in each air conditioner by the leakage rate and the total number of cars. So, annual leakage per car = 1.1 kg/car * 25% = 0.275 kg/car. Total annual leakage for all cars = 0.275 kg/car * 100,000,000 cars.

Determine the mass of chlorine in CFC-12

CFC-12 has the chemical formula \( \mathrm{CF}_2 \mathrm{Cl}_2 \), with two chlorine atoms per molecule. To find the mass of chlorine in 1 kg of CFC-12, we need to know the molar masses of the elements involved and use them to calculate the proportion of chlorine in CFC-12. Calculate the molar mass of CFC-12: Molar mass of C = 12.01 g/mol,Molar mass of F = 19.00 g/mol,Molar mass of Cl = 35.45 g/mol,Molar mass of \( \mathrm{CF}_2\mathrm{Cl}_2 \) = 2(12.01 g/mol) + 2(19.00 g/mol) + 2(35.45 g/mol). Then, calculate the mass of chlorine in 1 kg of CFC-12: Mass of Cl in CFC-12 = (Molar mass of Cl * 2) / Molar mass of \( \mathrm{CF}_2\mathrm{Cl}_2 \) * 1000 g/kg.

Calculate the total mass of chlorine released

To find the total mass of chlorine released into the atmosphere annually, multiply the total mass of CFC-12 leaked (from Step 1) by the proportion of chlorine in CFC-12 (from Step 2). Total mass of chlorine released annually = Total annual leakage for all cars (in kg) * Mass of Cl in 1 kg of CFC-12.

Convert the mass to the correct unit and round off

Ensure the final answer is in kilograms and rounded to two significant figures as per the requirement.

Key concepts

Ozone Layer Depletion

The ozone layer is a protective shield in the Earth's stratosphere that absorbs most of the sun's harmful ultraviolet (UV) radiation. Ozone depletion refers to the thinning of this layer, leading to an increase in UV radiation reaching the Earth's surface. This phenomenon poses a significant threat to all forms of life, contributing to increased incidence of skin cancers, cataracts, and can negatively affect the environment and ecosystems.

Chlorofluorocarbons (CFCs), like CFC-12 used in air conditioning systems, are potent ozone-depleting substances. Once released into the atmosphere, CFCs slowly ascend to the stratosphere, where they are broken down by UV light, releasing chlorine atoms. These chlorine atoms are highly reactive and can destroy ozone molecules at a rapid rate—a single chlorine atom can destroy thousands of ozone molecules over its atmospheric lifetime. The concern over ozone depletion led to the development of the Montreal Protocol, an international treaty designed to phase out the production and consumption of ozone-depleting substances, including CFCs.

CFC-12 Chemical Properties

CFC-12, also known as dichlorodifluoromethane, is a chlorofluorocarbon with the chemical formula \(\mathrm{CF}_2\mathrm{Cl}_2\). It is a colorless, volatile liquid that is inert, non-toxic, and non-flammable under normal conditions. Its stability allows it to reach the stratosphere intact, but this stability also means that CFC-12 has a long atmospheric lifetime, lasting for approximately 100 years. This prolonged presence in the atmosphere contributes significantly to ozone layer depletion once it releases chlorine atoms.

The specific chemical properties of CFC-12 contribute to its usefulness in air conditioning systems. With a boiling point of -29.8°C, it serves as an effective refrigerant. Although CFC-12 was once widely used due to these suitable properties, its detrimental environmental impact has led to its phase-out under international regulations. Replacements for CFC-12, such as hydrofluorocarbons (HFCs), have been developed to provide similar functionality without harming the ozone layer.

Atmospheric Pollution Calculations

Calculating atmospheric pollution involves quantifying the emissions of pollutants and their dispersal and concentration in the air. For ozone-depleting substances like CFC-12, it is crucial to determine the amount of chlorine released into the atmosphere, as chlorine is the active agent responsible for ozone layer depletion. The example provided describes a situation where each year, 25% of the CFC-12 in 100 million automobiles is leaked. This release can be calculated using a series of steps that provide conservationists and policymakers with estimates needed to assess environmental impact and develop regulations.

Firstly, the amount of CFC-12 leaked annually from each car is determined. Multiplying this by the number of cars gives the total annual leakage. The analysis is then extended to assess the amount of chlorine within the leaked CFC-12. This is done by determining the mass percentage of chlorine in CFC-12 and applying this to the total leaked mass. Lastly, the outcome is converted to a consistent unit and rounded as necessary. These calculations are pivotal for understanding and mitigating the effects of CFCs and other pollutants on the atmosphere.