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Mg

The essentials

Name: magnesium Symbol: Mg Atomic number: 12 Atomic weight: 24.3050 (6) CAS Registry ID: 7439-95-4

Group number: 2 Group name: Alkaline earth metal Period number: 3 Block: s-block

Here is a brief description of magnesium.

• Standard state: solid at 298 K
• Colour: silvery white
• Classification: Metallic
• Availability: magnesium is available in several forms including chips, granules, powder, rod, foil, sheet, rod, turnings, and ribbon.

Magnesium is a grayish-white, fairly tough metal.

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

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 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 picture above shows the result of setting off a mixture of magnesium metal with solid silver nitrate with water! Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment. Select a movie icon to see the result of setting off a mixture of magnesium metal and solid silver nitrate with water!

Magnesium metal burns with a very bright light. The picture above shows the colour arising from adding magnesium powder to a burning mixture of potassium chlorate and sucrose. Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment.

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.

Isolation

Here is a brief summary of the isolation of magnesium.

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.

posted by Yamhill @ 11:24 PM