Saturday, March 22, 2014

Magnesium - Chemistry

Magnesium occupies sixth position in order of the abundance on earth.

Magnesium is greyish white metal.

Magnesium is the lightest metal used in industry and it has a density less than two thirds of aluminium. Magnesium is an important alloying metal.


Some of the alloys of magnesium containing more than 90% magnesium and 2 to 9% of Aluminium and 1% zinc are used in automobile engines, in aircrafts and in making balances.
Up to 5% magnesium is added to most commercial aluminium alloys (duralumin, magnalium) to improve its resistance to corrosion, mechanical properties and weldability.

Magnesium is used as a reducing agent in metallurgy for the production of metals such as Titanium (Ti), Zirconium (Zr) and Hf.

Magnesium power is used in fireworks.

It is part of alkyl magnesium halide (RMgX), the Grignard reagent and it is useful for making numer of organic compounds.

Magnesium hydroxide and magnesium carbonate are used in making toothpastes.

Magnesium hydroxide (milk of magnesia) is used as an antacid. It neutralises excess of acid in stomach and thus it is used as medicine.

Ores of Magnesium

1. Carnallite
2. Magnesite
3. Dolomite
4. Epsom salt or epsomite
5. Langbeinite
6. Asbestos

Extraction of Magnesium from Its Ores

Magnesium is finally extracted by the electrolysis of its molten anhydrous salts.

From Magnesite
The ore MgCO3 is calcined to form the oxide MgO.
The oxide is mixed with carbon and heated in a current of Cl2 gas to form magnesium chloride.
Magnesium chloride is subjected to electrolysis.

Electrolysis of Magnesium chloride

Magnesium chloride is with a mixture of sodium chloride and calcium chloride and heated to 973 K - 1023 K. The mixture melts at this temperature and the electrolysis in carried out in an iron vessel which serves as the cathode.  A graphite rod serves as anode. During the electrolysis an inert gas such as coal gas is passed through the cell to check the oxidation of magnesium. At cathode magnesium will emerge in molten state and at anode chlorine gas will be released. The liquid magnesium (m.p. 924K) is removed from time to time from the top of the vessel.

Magnesium is a s-Block element.