[Chemistry Class Notes] on Chlorofluorocarbon Pdf for Exam

Chlorofluorocarbons (CFCs) are non-flammable, non-toxic substances that are partially or totally halogenated paraffin hydrocarbons with just hydrogen (H), carbon (C), fluorine (F), and chlorine (Cl). It is produced as volatile derivatives of methane (CH₄), ethane (C₂H₆), and propane (C₃H₈). CFC full form is related to the name of atoms from which it is composed; it is a chlorofluorocarbon.

Many chlorofluorocarbons have been widely used as propellants in applications for aerosol, refrigerants and solvents. The manufacture of such compounds has been phased out under the Montreal Protocol as they contribute to the depletion of the ozone layer in the upper atmosphere. Because of this, CFCs are being replaced with other products such as hydrofluorocarbons (HFCs) that include R-410A and R-134a.

Preparation of Chlorofluorocarbons

Chlorofluorocarbons are generally prepared from chlorinated methanes and ethanes through the exchange of halogen. The synthesis reaction of chlorodifluoromethane from chloroform (CHCl₃) is as follows.

                                      CHCl₃ + 2HF → HCF₂Cl + 2HCl

Properties of Chlorofluorocarbons

Carbon in the CFCs makes bonding with tetrahedral symmetry. The Chlorofluorocarbons, which are derived from CH₄, deviate from the geometry of perfectly shaped tetrahedral symmetry. Some of the properties of CFCs are given below.

1. Chlorofluorocarbons are competitively less volatile than their parent alkanes. The boiling point of CH₄ (methane) is −161⁰C, whereas the boiling point of the chloromethane is between −51.7 ⁰C (CF₂H₂) and −128⁰C (CF₄).

2. The densities of chlorofluorocarbon used to be higher than its corresponding alkanes. The density of these compounds has correlated with the number of chlorides.

3. These are odourless, very less flammable and tasteless. These compounds are chemically stable.

4. These are competitively less flammable than methane (CH₄), because of the presence of less Carbon and Hydrogen bonding.

Examples of CFCs

Some important CFCs examples are as follows.

CFC-11 is trichlorofluoromethane which is also termed freon-11 or R-11. It is a CFC. It is a faintly ethereal, sweetish-smelling and colourless liquid. It boils at room temperature. CFC-11 comes under substances that damage the protective ozone layer of the earth.

                               

 

CFC-12 is dichloridofluoromethane which is a colourless gas. CFC-12 is generally manufactured under the brand name Freon-12.  Through the reaction of carbon tetrachloride (CCl₄) with hydrogen fluoride (HF), dichlorodifluoromethane/CFC-12 can be prepared.

Carbon tetrachloride has the chemical formula CCl₄. It is a colourless liquid having a sweet type of smell that can be detected at low levels. At low temperatures, it is practically not flammable.

1,1,1-trichloroethane is also an organic compound that is popularly known as methyl chloroform. It is chloroalkane as it is derived from an alkane. This is also colourless like most of the CFCs and the sweet-smelling liquid. It was once produced industrially in large quantities for the purpose to use as a solvent.

          

The Ozone Layer Depletion

There is a thin layer of ozone particles present in the stratosphere approximately 20 km to 30 km from the surface of the earth. The ozone layer absorbs the Ultraviolet traditions that come from the sun to the earth, and hence it protects everyone from exposure to deadly radiation of UV. An ozone molecule is composed of three oxygen atoms (O₃). Life on Earth would be very difficult without the ozone layer in the atmosphere. 

The harmful effects of the ozone layer on human health are observed as exposure to ozone can cause difficulty in breathing, coughing and shortness of breath. It can lead to worse health conditions such as asthma, damaged airways, emphysema, chronic bronchitis, asthma etc. Ozone can continue to damage the lungs even after symptoms have disappeared.

Some chemical compounds are depleting the ozone layer, which is very dangerous for living beings as well as for the environment. Chlorofluorocarbons (CFCs), halons and hydrofluorocarbons (HCFCs) are such compounds that destroy ozone in the upper atmosphere (stratosphere).

                

The major cause of the depletion is halogenOzone. CFCs is a non-reactive compound, so it migrates to the stratosphere with the wind. The radiation coming from the sun breaks down the CFC molecules and produces free atoms of chlorine. These atoms further react with ozone (O₃) and reduce it to O₂. This is a cyclic process where the continuous breakdown of ozone molecules happens. The most severe depletion in the ozone layer has occurred in the south pole. It was first seen in Antarctica.

Do You Know?

Representatives of 24 countries in 1987 came together and met together in Montreal, Canada. They all agreed on a protocol called the Montreal Protocol to reduce the use of substances that are depleting the ozone layer. Besides this in the year 2016, a group of scientists brings out that the ozone layer is slowly healing, which is proof that the Montreal Protocol is successfully working. It is estimated that by the 21st century, the ozone hole of Antarctica will completely heal.

Conclusion

Chlorofluorocarbon is used for many purposes, but it is harmful to the environment as it depletes the ozone layer; hence, we should try to reduce the applications of CFCS that affect our environment.