ISOLATION OF FLUORINE
Symbol - F Atomic number -9 Period Number :2
Valency -1 Atomic mass-19 Group Number : 17
Fluorine does not occur free in nature. It occurs in the combined form.
Dennis' Method: This was devised by Dennis, Veeder and Rochow in 1931.
In this fluorine is prepared by the electrolysis of fused sodium or potassium hydrogen fluoride (perfectly dry) Electrolysis is carried out between graphite electrodes in a V-shaped electrically heated copper tube. The ends of the tube are covered with copper caps into which the graphite electrodes are fixed with bakelite cement. The copper tube is thickly lagged to prevent loss of heat.
KHF2 ® KF + HF
HF ® H+ + F¯
2H+ + 2e- ® H 2 (At cathode)
2F - - 2e- ® F2 (At anode)
Fluorine liberated at the anode is passed through the U-tube containing
sodium fluoride. Thisremovesthe hydrogen fluoride vapourscomingwithfluorine.
NaF +HF ® NaHF2
1. Fluorine is a gas and has pale greenish yellow colour.
2. It has extremely pungent and penetrating odour. 3. It is heavier than air.
Fluorine is the most active member of halogen family.
1. Action with Hydrogen: Hydrogen explodes violently in fluorine even in the dark.
H2 + F2 ® 2HF
2. Action with non-metals: Non-metals like carbon, silicon and phosphorus burn in fluorine forming fluorides.
C + 2F2 ® CF4
Si + 2F2 ® SiF4
2P + 5F2 ® 2PF5
3. Action with metals: It reacts with metals forming corresponding fluorides.
2Ag + F2 ® 2AgF
2Al + 3F2 ® 2AlF3
4. Formation of Interhalogen compounds: It forms a variety of inter halogen compounds with other halogens.
Br2 + 3F2 ® 2Br F3
I2 + 5F2 ® 2 IF5
1. Fluorine is used in the manufacture of a series of compounds known as
freons. These non-toxic, non-combustible and volatile liquids are used as refrigerants in refrigerators, deep freezers and air conditioners. The most
common, freon is known as dichlorodifluoro methane CF2 Cl2.
2. CaF2 is used as flux in metallurgy.
3. NaF is used as a preservative to prevent fermentation and also for preventing dental cavities.
4. SF6 is used as an insulating material in high voltage equipment.
5. Teflon is used as container to store hydrofluoric acid.
6. UF6 is used in the separation of U235 from U238.
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