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Freons are the chlorofluorocarbons, which are obtained by replacing the hydrogen atoms from methane (CH4). These are important polyhalogen compounds and are used in different industries. For instance, CCl4 (carbon tetrachloride) was used as a cleaning fluid earlier, CCl4 is also used as a fire extinguisher, and as a fumigant to kill harmful bacteria and insects in the grains. DDT or dichloro-diphenyl-trichloroethane is a colourless crystalline solid organochlorine. It is tasteless and odorless. DDT is produced by performing a reaction between chloral and chlorobenzene. DDT is insoluble in water but is readily soluble in organic solvents like fats and oils. CCl4 is obtained by replacing all four atoms of hydrogen with Chlorine from the Methane (CH4). CCl4 is highly toxic to inhale, causes skin diseases and is one of the main reasons for global warming.
| Table of Contents |
Key Terms: Freons, DDT, Carbon Tetrachloride, Polyhalogen Compounds, Chlorofluorocarbons, Bacteria, Methane, Crystalline solid, Organochlorine, Organic solvents
Tetravalency of Carbon
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Carbon has a symmetrical electronic configuration and does not allow any transfer of electrons in any direction. That is why carbon makes covalent bonds only, as the number of unpaired electrons in the outermost shell is 4 which is why carbon is able to make 4 bonds easily. This is the reason why carbon is tetravalent. Because of the tetravalency of carbon, carbon is able to form long compounds by forming covalent bonds with other atoms. Organic chemistry is the chemistry that deals with organic compounds and organic compounds are the compounds made up of Carbon and Hydrogen.
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| Chapter Related Concepts | ||
|---|---|---|
| Ester Hydrolysis | Fehling Test | Iodoform Test |
| Hell-Volhard-Zelinsky Reaction | Friedel-Crafts acylation reaction | Butyric Acid |
Polyhalogen Compound
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Polyhalogen compounds are carbon compounds with more than one halogen atom attached to the carbon atom through a covalent bond. Halogens are the highly reactive elements of group 17, they only require 1 extra electron to complete their octet in order to meet stable electronic configuration. Methyl chloride, chloroform, carbon tetrachloride, iodoform, DDT, benzene hexachloride, CFCs etc. are some of the most important polyhalogen compounds. Polyhalogen compounds are used in many ways ranging from agricultural to medicinal uses. For example-
- Dichloromethane is used for the production of paint removers.
- Dichloromethane is also used for propelling aerosols.
- CH2Cl2 is also an important solvent for the manufacturing of drugs.
- Polyhalogen compounds are used in bleaching processes.
- Chloroform I used in the production of the freon refrigerant R-22, which is responsible for the cooling property in the air conditioners and refrigerators.
- Iodoform was used as an antiseptic in earlier days. But now is replaced by iodine only.
- DDT is mainly used for propelling mosquitos and lice.
Carbon Tetrachloride (CCl4)
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Carbon tetrachloride is also known as tetrachloromethane, it has 1 carbon atom and 4 chlorine atoms (CCl4). CCl4 is a poly halogen compound with 4 chlorine atoms as the functional group. In normal conditions, CCl4 is colourless with a sweet odour. In the past days, it was mainly used as a cleaning agent. It was also used in fire extinguishing products and in refrigerants, but because of its toxicity, the use of CCl4 is prohibited by several governments.
Uses of CCl4
The uses of CCl4 include:
- CCl4 is used in the production of refrigerants and aerosol propellants.
- CCl4 also has cleaning properties so it was widely used as a cleaning product, and spot removers.
Harmful effects of CCl4
CCl4 is a very toxic material and cause severe damage to the body of a human being and nature. The hepatotoxin behaviour of the compound can cause severe damage to the liver and some can cause complete failure of the liver. CCl4 can cause damage to the central nervous system. Direct exposure with CCl4 for more time can even result in a coma or sometimes even death of the person. Cancer and kidney damage can also be caused because of exposure to the CCl4.
Structure of CCl4
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The geometry of CCl4 is tetrahedral and it has 4 chlorine atoms attached to one carbon atom present in the central position.
Structure of CCl4
In CCl4 all the 4 electrons present in the valence shell of the carbon atom participate in the bond formation by combining (making a bond) with the chlorine atoms. CCl4 exhibit sp3 hybridization as 1s and 3p orbitals of carbon participate in the bond-forming process. Because of inter-electronic repulsion due to unbonded electrons, the bond angle becomes 109.5 resulting in the tetrahedral shape of the compound.
Freons
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Freons is the other name for the (CFCs) Chlorofluorocarbons. CFCs are compounds that contain carbon, chlorine, and fluorine. Freons are important polyhalogen compounds. CFCs are formed by replacing the Hydrogen atoms of methane with the atoms of chlorine and fluorine. All organic compounds that contain carbon, chlorine, and fluorine are CFCs but CCl2F2 is the most common and most used freon. CCl2F2 is produced from the tetrachloromethane by performing the Swarts reaction.
Freons
These are highly stable, non-corrosive, non-toxic and nonreactive compounds that are used for refrigerant purposes. Its easily liquefiable property makes it easier to be transported from one place to another. CCl2F2 is a colourless gas with a faint ethereal odour. Long exposure to the heat can cause rupturing of the containers.
DDT (p, p’-Dichlorodiphenyltrichloroethane)
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DDT or Dichlorodiphenyltrichloroethane is an organochlorine with no colour, taste, or odour. It has a crystalline solid structure and is known for its insecticidal and pesticidal behaviour. It is mainly used by farmers as insecticides and pesticides. DDT is produced by performing a reaction between chloral and chlorobenzene. DDT is insoluble in water but is readily soluble in organic solvents like fats and oils. The extensive use of DDT in farming is prohibited. DDT is extensively used in the manufacturing industries of various aerosols and vaporizers, lotions, emulsifiable concentrates, etc. DDT is a very effective propellant for malaria spreading mosquitoes and typhus causing lice. It is the main reason for the popularity of the DDT as it was extensively used for the safety of the war troops. As it is highly unstable, DDT is very reactive and is soluble in fat, it is banned in many countries as it has many ill effects.
Things to remember
- CCl4 is used in the production of refrigerants and aerosol propellants.
- DDT is insoluble in water but is readily soluble in organic solvents like fats and oils.
- CCl2F2 is a highly stable, non-corrosive, non-toxic and non-reactive compound.
- DDT is highly unstable, very reactive and is soluble in fat.
- DDT is mainly used by farmers as insecticides and pesticides.
- DDT is banned in many countries as it has many ill effects.
- Chlorofluorocarbons are also referred to as Freons.
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Sample Questions
Ques. What are polyhalogen compounds? (3 marks)
Ans. Polyhalogen compounds are organic compounds that are comprised of carbon, hydrogen and elements of the halogen family. Polyhalogeno compounds are mainly formed by replacing hydrogen atoms of the hydrocarbons with the atoms of halogen atoms. CCl4 (carbon tetrachloride) is formed by eliminating hydrogen atoms from the methane and replacing them with chlorine atoms.
Ques. Explain the structure of Carbon Tetrachloride? (3 marks)
Ans. The molecules of Carbon tetrachloride exhibit tetrahedral geometry. The carbon atom placed at the central position is bonded with the 4 chlorine atoms with a single covalent bond. The unpaired electrons present in the carbon atom results in the inter-electronic repulsion and makes the bond angle 109.5 degrees. The covalent bonds of the molecule make the compounds non-polar. The hybridization of the compound is sp3 because the bonding is done with 1 s electron and 3 p electrons of the carbon atom.
Ques. Write a short note on freons? (3 marks)
Ans. Freons are chlorofluorocarbons that comprise carbon, fluorine, and chlorine. The properties of different CFCs is mainly determined by the number of fluorine and chlorine atoms and also by their positions. The CFCs are written as CFC-n. where n is the number of atoms in the concerned CFC compound. The freons were initially used as refrigerants, and now these are also used in perfume, body sprays, aerosols, etc.
Ques. Discuss the physical and Chemical properties of DDT? (5 marks)
Ans. Some physical and chemical properties of DDT are:-
- The chemical formula for DDT or dichlorodiphenyltrichloroethane is C14H9Cl5
- The molar mass of DDT is 354.8 grams per mole.
- The DDT is nearly insoluble in water
- The density of DDT is 1 gram per cubic centimetre (in standard condition).
- The melting point of the compound is 108.5 degrees Celsius or 381.5 kelvin.
- The boiling point of DDT is 260 degree Celsius and at this temperature the compound undergoes decomposition.
- The solubility value of DDT in water is 25 micrograms in a litre of water.
Ques. What are the main disadvantages of Freons? (5 marks)
Ans. Freons or chlorofluorocarbons are mainly used in refrigerants and air conditioners. But nowadays due to their adverse effect on nature people are trying to minimize the production and use of chlorofluorocarbons. Scientists arrived at an observation that the CFCs in nature goes towards the ozone layer (O3), where the C-Cl bond breaks due the U-V radiations from the sun and leaves the Cl radical in nature near the O3. Now, this free radical reacts with the O3 to give an oxygen molecule and an oxygen free-radical and this reaction undergoes again and again as a chain reaction. And after this process, the ozone loses its strength and becomes thinner day by day.
Ques. Discuss the properties of Carbon Tetrachloride? (3 marks)
Ans. Some physical and chemical properties of CCL4 are: -
- The molecular mass of carbon tetrachloride is 153.81 grams per mole.
- The compound is liquid in the standard conditions.
- It is colourless and has a sweet odour.
- It has a density of 1.5867 grams per cubic centimetre.
- CCl4 is not soluble in water.
- CCl4 has tetrahedral geometry.
Ques. What are the Uses of DDT and discuss its disadvantages? (3 marks)
Ans. DDT or dichloro-diphenyl-trichloroethane is used as an insecticide and pesticide in the agricultural field and is also known for its pest-controlling properties. Manufacturing of DDT is easy, it is chemically stable and is cheap. But is generally denied use because of its ill effects on the environment. It can be present in the environment for more than a decade without any degradation. It can also pollute the air by entering the top layer of the atmosphere.
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