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FLUORINE

Fluorine is a poisonous pale yellow gaseous element and belongs to the group VII of the periodic table. Fluorine is the most electronegative element and also the strongest oxidizing agent known. It is characterised by

1. Atomic number 9
2. Relative atomic mass 18.9984
3. Density 1.7g/dm³
4. Melting point -219^OC
5. Boiling point -1881^OC
6. It has a pungent odour ( the odour resembles that of a mixture of ozone and chlorine)

PREPARATION

The principal source of fluorine is the mineral fluorspar, CaF₂. This substance is treated with concentrated H₂SO₄ to make HF. Since HF is more reactive than the element fluorine, it corrodes the vessel and thus this method is not used.

In the modern method, elemental fluorine is prepared by electrolysis of the molten salt, KHF₂. The electrolysis produces H₂ and F₂. The electrolytic cells are made up of copper, nickel or monel metal. The reactions are as follows

KHF_{2 è} KF + HF

KF è K⁺ + H^-

At anode

F- è F + e^-

2F è F₂

At cathode

K⁺+ eè K

K+HF è KF + H

2H è H₂

CHEMICAL PROPERTIES

1. Because of its very high reactivity, it can displace all halogens from their halides

F₂ + 2NaX è 2NaF + X₂

2. It combines with most of the metals and non-metals to form corresponding fluorides

Mg + F_{2 è} MgF₂

C + 2 F₂ è C F₄

NOTE: Hydrogen explosively reacts with fluorine (even in dark)

H₂ + F_2è H₂ F₂

NOTE: A mixture of oxygen and fluorine explodes in the presence of an electric discharge.

O₂ + F_2è O₂ F₂

1. Oxidising property

Fluorine is a very strong oxidising agent

KClO₃ + F₂ + H₂O è KClO₄ + H₂ F₂

2NaHSO₄ + F₂ è Na₂S₂O₈ + 2HF

1. At 100^OC it reacts with glass

SiO₂+ 2F₂ è SiF₄ + O₂

USES

• It is used in the preparation of fluorides.
• It is used as an insecticide.
• It is used as an oxidising agent ( specially in rockets).

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