Magnesium

Magnesium: the essentials

 Brief description: magnesium is a grayish-white, fairly tough metal. Magnesium is the eighth most abundant element in the earth's crust although not found in it's elemental form. It is a Group 2 element (Group IIA in older labelling schemes). Group 2 elements are called alkaline earth metals. Magnesium metal burns with a very bright light.

Magnesium is an important element for plant and animal life. Chlorophylls are porphyrins based upon magnesium. The adult human daily requirement of magnesium is about 0.3 g day^-1.

Table: basic information about and classifications of magnesium.

Name: Magnesium Symbol: Mg Atomic number: 12 Atomic weight: 24.3050 (6) Standard state: solid at 298 K CAS Registry ID: 7439-95-4

Group in periodic table: 2 Group name: Alkaline earth metal Period in periodic table: 3 Block in periodic table: s-block Colour: silvery white Classification: Metallic

Small and large samples of magnesium rod like this, as well as foil and sheet, (and magnesium alloy in foil form) can be purchased from Advent Research Materials via their web catalogue.

Magnesium tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame. Normally magnesium is coated with a layer of oxide, MgO, that protects magnesium from air and water.

The result of aqueous ignition of a mixture of magnesium metal with silver nitrate with water (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard asessment). Improperly done, this reaction is dangerous!

The picture above shows the colour arising from adding magnesium powder to a burning mixture of potassium chlorate and sucrose (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard asessment).

Isolation

Isolation: magnesium can be made commercially by several processes and would not normally be made in the laboratory because of its ready availability. There are massive amounts of magnesium in seawater. This can be recovered as magnesium chloride, MgCl₂ through reaction with calcium oxide, CaO.

CaO + H₂O → Ca²⁺ + 2OH^-

Mg²⁺ + 2OH^- → Mg(OH)₂

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Electrolysis of hot molten MgCl₂ affords magnesium as a liquid whih is poured off and chlorine gas.

cathode: Mg²⁺(l) + 2e^- → Mg

anode: Cl^-(l) → ¹/₂Cl₂ (g) + e^-

The other methos used to produce magnesium is non electrolytic and involves dolomite, [MgCa(CO₃)₂], an important magnesium mineral. This is "calcined" by heating to form calcined dolomite, MgO.CaO, and this reacted with ferrosilicon alloy.

2[MgO.CaO] + FeSi → 2Mg + Ca₂SiO₄ + Fe

The magnesium may be distilled out from this mixture of products.

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Magnesium	Magnésium
Magnesium	Magnesium
Magnesio	Magnesio
Magnesium	Magnésio