Fluorine

Fluorine, F2, is a poisonous pale yellow gaseous element found in Group VIIb (i.e. the Halogen Group of elements) of the periodic table.

Atomic Number : 9
Atomic Mass : 18.9984
Melting Point : -219.62 degC
Boiling Point : -188.1 degC
Density : 1.7

The liquid has a clear yellow colour.

Fluorine is a highly dangerous element, causing severe chemical burns on contact with the skin.

Discovery

Fluorine was first identified by Scheele in 1771AD.
Fluorine was first isolated by Moissan in 1886AD, when he noted the inclusion of fluorine in crystals of fluorspar from Quincie.

Occurrence

Fluorine is an element which widely distributed, but not very abundant. However, because of its high reactivity is not found naturally in its elemental state.

Cryolite, Na3AlF6,
Fluorspar, CaF2, and
Fluorapatite, 3Ca3(PO4)2.Ca(ClF).

Extraction

Preparation

Fluorine can be prepared by the electrolysis of fused acid potassium fluoride at 373 degK in a copper vessel using graphite electrodes. The electrolyte, pure and dry acid potassium fluoride is fused in an electrically heated vessel, such as a wide copper V-tube, the electrodes are pure acheson graphite rods insulated in bakelite cement stoppers. A current of 5 amperes at 12 volts is used. The fluorine is purified by passage through two copper U-tubes, containing dry sodium fluoride.

Manufacture

Fluorine is made on the industrial scale by the electrolysis of fused acid potassium fluoride in a copper vessel using graphite electrodes at currents up to 2,000 amperes. An anode current efficiency of about 95% was attained. The fluorine gas is then piped in steel or copper vessels and compressed up to 400 lb/in2 in nickel and steel cylinders.

Properties

Fluorine is a light canary-yellow gas at room temperature.
Fluorine is the most reactive and electronegative of all elements.

Reactions

Fluorine reacts explosively with hydrogen even in the dark and at low temperature.
Fluorine reacts violently with water forming hydrogen fluoride, and liberates oxygen which is highly charged with ozone.
2 F2 + 2 H2O ==> 4 HF + O2
Fluorine also reacts with sulphur, selenium, and tellurium, which melt and ignite in the gas, forming halides.
Fluorine is a powerful oxidising agent. For example, when fluorine is bubbles through a solution of potassium chlorate this is oxidised to potassium perchlorate.
F2 + 2 KClO3 + H2O ==> 2 HF + KClO4
Fluorine does not react directly with oxygen, or nitrogen, and combines with chlorine, only on heating, forming the gaseous products chlorine fluoride, and chlorine trifluoride.
Fluorine readily combines with bromine, and iodine, forming colourless liquids BrF3 and IF5.

Uses

Fluorine is used in the synthesis of organic fluorine compounds.

Fluorine is used in the manufacture of Freon (i.e. dichlorodifluoromethane, CCl2F2) which is used as a refrigerant.

Fluorine is used in the manufacture of uranium hexafluoride which is required for the separation of the isotopes of uranium in centrifuges.

Detection and Analysis

Fluorine is detected by its corrosive action on glass (i.e. the glass is etched).

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