Fluorine

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Table Of Content

What is Fluorine?


Fluorine is the first chemical element of the Halogen family. It is represented by symbol F and has atomic number 9. Fluorine is an extremely reactive element and reacts with itself to form Fluorine Gas (F2 (g)) which has light yellow color. It is the 13th most abundant element by weight.

Fluorine

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Who Discovered Fluorine?


During 1813, Humphry Davy performed set of experiments and proved the presence of new element, which he called Fluorine. Though his experiments established the presence of Fluorine, he was unable to collect samples of it. In 1886, Moissan prepared Fluorine for the first time. For his contribution he was awarded Nobel Prize in Chemistry in 1906.

Humphry Davy

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Occurrence of Fluorine


Fluorine is found in earth’s crust in different forms. The major naturally occurring are:

Fluorspar or Fluorite (CaF2)

The name is given fluorspar because the compound produces fluorescence when heated.

Fluorspar or Fluorite

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Fluoroapatite [3(Ca3 (PO4)2.CaF2)]

This is major source to produce Phosphorous. As the gangue particles present along with this compound is Silicon Dioxide (SiO2), Fluoroapatite cannot be used to manufacture Hydrogen Fluoride (HF) and Fluorine. This is because the HF so produced reacts with SiO2 to form Silicic acid (H2 [SiF6]).

Fluoroapatite

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Cryolite (Na3AlF6)

It is basically used in the extraction of Aluminum from its Bauxite ore.

Cryolite

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Production of Fluorine


Calcium fluoride (CaF2) or Fluorspar is used for the preparation Fluorine Gas. When Calcium fluoride reacts with Sulphuric Acid (H2SO4), Calcium sulfate (CaSO4) and Hydrogen fluoride (HF (aq)) is formed.

Calcium fluoride reacting with Sulphuric Acid to produce Calcium Sulphate

Then, aqueous HF is distilled to get anhydrous HF (l) which undergoes electrolysis in presence of Potassium Fluoride (KF) and converts to Potassium Bifluoride (KHF2)

Potassium Fluoride reacting with Hydrogen fluoride to produce Potassium Bifluoride

Further electrolysis of K [HF2] produces F2 (g) and H2 (g).

Electrolysis of Potassium Bifluoride

In above process Hydrogen Gas (H2 (g)) is liberated at cathode and Fluorine Gas (F2 (g)) is liberated at anode.

Difficulties Arising in Manufacturing of Fluorine


  • Hydrogen fluoride is corrosive in nature. It etches glass and causes painful wounds of skin. The wound heals slowly because Fluoride ions (F-) remove Calcium ions (Ca2+) from the tissue.
  • Water (H2O) must be removed as soon as it is formed because F2 (g) will oxidize water to Oxygen gas (O2 (g)).
  • The Hydrogen Gas liberated at cathode and Fluorine Gas liberated at anode, must be separated by a diaphragm, otherwise they will undergo reaction violently.
  • Fluorine is extremely reactive and it attacks glass and metals. Therefore it becomes really difficult to identify the metal to form the reaction vessel. Moissan used Platinum U-Tube to extract the Fluorine Gas. As Platinum is very expensive, either Copper (Cu) or Monel metal (Cu/ Ni alloy) is used as material for reaction vessel. Also surface of the vessel is covered with a layer of fluoride film to slow down further attack.
  • Graphite anode must not be used since graphite reacts with Fluorine forming Graphite-Fluorine compound, CF. Due to formation of this compound the gap widens up gap between the graphite sheets and ceases conduction by graphite. To avoid formation of Graphite-Fluorine compound, ungraphitized carbon (Powdered coke + Copper) is used.

Unique Characteristics of Fluorine


Fluorine as the first member of the Halogen Family significantly differs from the rest of the members of the group .This is because of the following reasons

  1. Fluorine is small in size
  2. Fluorine is the highest electronegative element known.
  3. Fluorine has absence of d orbital in second shell. Therefore it cannot show variable oxidation state like other members of the group and shows only minus one as oxidation state (-I).
  4. Fluorine is strongest oxidizing agent. Therefore it brings out the highest oxidation state of other elements with which it forms compounds Eg IF7, SF6 etc.

Uses of Fluorine


  • Small amount of Fluoride ion (F-) in drinking water reduces the problem of tooth decay, as it makes the enamel stronger by converting Hydroxyapatite [3Ca3 (PO4)2.Ca (OH) 2] into Fluoroapatite [3Ca3 (PO4)2.CaF2] which is much stronger and harder than former compound. However, high concentration of F- ion in drinking water increases the problem of discoloration and brown molting of teeth.

Fluorine is used for separation of isotopes of uranium by gaseous diffusion of UF6. Gaseous diffusion is used for enrichment of uranium fuel for nuclear reactor.

Equations for separation of Isotopes of Uranium

Equations for separation of Isotopes of Uranium

  • Fluorine is used for manufacture of chlorofluorocarbons (CFCs) which are used as refrigerant, aerosol propellants and foaming agent in polymers. CFCs are also used in artificial blood. Freons which are mixed chlorofluorocarbon are important as they are used also used as refrigerant.
  • Fluoroalkene an important compound of Fluorine on polymerization gives Teflon which is used for making non-sticking cooking pans.

Tetrafluoro ethane to Teflon

  • Fluorine is used for manufacturing of SF6 (g) which is very inert gas ever under high temperature and voltage conditions and can be used as dielectric medium.
  • Fluothane CF3CHBrCl is used as anesthetic.
  • Fluorine is used for manufacture of Aluminum Fluoride (AlF3) and Cryolite (Na3 [AlF6]).
  • Fluorine is used for synthesis of many fluorinating agents ClF3, BeF3 etc.

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