Freons, i.e., chlorofluorocarbons (CFC) have been widely used as refrigerants and as propellants in aerosols and foams. But theiir persistent use has depleted the ozone layer which has led to global warming. Consequently, use of freons as refrigerants and propellants in aerosols has beenn banned in USA and many other countries. during the past few years, search for effective substitutues for freons have been successful. Now answer the following questions: (i). What is freon-12? How is it prepared? (ii) How does freon-12 deplete ozone layer?

Freons, i.e., chlorofluorocarbons (CFC) have been widely used as refri

1.	Freons, i.e., chlorofluorocarbons (CFC) have been widely used as refrigerants and as propellants in aerosols and foams. But theiir persistent use has depleted the ozone layer which has led to global warming. Consequently, use of freons as refrigerants and propellants in aerosols has beenn banned in USA and many other countries. during the past few years, search for effective substitutues for freons have been successful. Now answer the following questions: (i). What is freon-12? How is it prepared? (ii) How does freon-12 deplete ozone layer?
Answer» Solution :(i) Freon-12 is dichlorodifluoromethane `(C Cl_(2)F_(2))`. It is prepared from carbon tetrachloride by Swarts reaction. `3 C Cl_(4)+2SbF_(3) overset(SbCl_(5))to underset("Freon-12")(3C Cl_(2)F_(2))+2SbCl_(3)` (ii) SINCE freons are non-biodegradable. they diffuse into the STRATOSPHERE. there, above the protective ozone layer, the highly energetic UV rays cleave one of the C-Cl bonds and initiates a SERIES of reactions. STEP 1: `C Cl_(2)F_(2)overset(hv)toC ClF_(2)+Cl` ltBrgt Step 2: `Cl+O_(3)toClO+O_(2)` Step 3: `ClO+OtoCl+O_(2)` The formation of ANOTHER chlorine radical in step (3) can decompose another molecule of `O_(3)`. the steps (2) and (3) are repated mahy times. as a result, decomposition of one `C Cl_(2)F_(2)(CFC)` molecule can bring about the destruction of thounsands of molecules of ozone.