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Magnesium Chloride »
Magnesium Chloride, MgCl2
Anhydrous MgCl2 is white, deliquescent, and soluble in water with great evolution of heat. It is formed by the action of chlorine on the metal or on heated magnesium oxide, or, more easily, on a heated mixture of magnesium oxide and carbon.
It has also been prepared by heating NH4Cl.MgCl2.6H2O, by heating the hydroxide in hydrogen chloride, and by heating the hexa-hydrate in vacuo at 175° C.
It is easily distilled in a current of hydrogen, and the cooled product crystallises into shining laminated crystals that have a density of 2.177 and melt at 708° C.
Between 580° C. and 700° C. the reaction
2MgCl2+O2 ⇔ 2MgO+2Cl2
is endothermic.
Between 350° C. and 505° C. the reaction
MgCl2+H2O ⇔ MgCl (HO)+HCl
is exothermic. The oxychloride decomposes from 505°-510° C., and above the latter temperature the reaction
MgCl2+H2O ⇔ MgO+2HCl
is endothermic. Hydrogen chloride has been prepared by this last reaction.
The monoetherate, MgCl2.Et2O, has been obtained in white acicular crystals.
MgCl2.4NH4 has been prepared as an easily decomposable compound, and MgCl2.6NH4 has also been reported.
When a solution of oxide or carbonate of magnesium in hydrochloric acid is crystallised, the hexahydrate, MgCl2.6H2O, separates as colourless monoclinic crystals with a density of 1.56 and a bitter taste. The hexahydrate is stable in contact with the saturated solution of magnesium chloride from -3.4° to 116.7° C. From 116.7° to 181° C. the tetrahydrate is the stable form and the dihydrate above 181° C. From -3.4° to –16.8° C. the α-octahydrate is stable. Between -9.6° C. and -17.4° C. a labile solution may be in equilibrium with the labile β-octahydrate. The dodecahydrate is the stable form from -16.8° to -33.6° C.: the crystals are lighter than their mother-liquor.
A monohydrate has been prepared by heating the tetrahydrate above 111° C. in hydrogen chloride, and a dihydrate has been obtained as small,white, deliquescent crystals from a solution of the chloride in hydrochloric acid.
The hexahydrate is obtained as a by-product in the preparation of potassium chloride from carnallite, in the Weldon process, and in the Solvay alkali process.
Concentrated solutions of magnesium chloride dissolve oxide or carbonate of lead, lead sulphate, and small amounts of zinc oxide.
One hundred parts of water dissolve 52.2 parts of MgCl2 at 0° C., and the density of the saturated solution at 15° C. is 1.3619.
The solubility of MgCl2.6H2O in parts of MgCl2 per 100 parts solution is -
MgCl2 and MgCl2.6H2O are soluble in alcohol.
[Mg] + (Cl2) = [MgCl2] + 151.01 Cal.
[MgCl2]+Aq. = MgCl2.Aq.+35.92 Cal.
[MgCl2.6H2O]+Aq. = MgCl2.Aq. +2.937 Cal.
It has also been prepared by heating NH4Cl.MgCl2.6H2O, by heating the hydroxide in hydrogen chloride, and by heating the hexa-hydrate in vacuo at 175° C.
It is easily distilled in a current of hydrogen, and the cooled product crystallises into shining laminated crystals that have a density of 2.177 and melt at 708° C.
Between 580° C. and 700° C. the reaction
2MgCl2+O2 ⇔ 2MgO+2Cl2
is endothermic.
Between 350° C. and 505° C. the reaction
MgCl2+H2O ⇔ MgCl (HO)+HCl
is exothermic. The oxychloride decomposes from 505°-510° C., and above the latter temperature the reaction
MgCl2+H2O ⇔ MgO+2HCl
is endothermic. Hydrogen chloride has been prepared by this last reaction.
The monoetherate, MgCl2.Et2O, has been obtained in white acicular crystals.
MgCl2.4NH4 has been prepared as an easily decomposable compound, and MgCl2.6NH4 has also been reported.
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Stable solution of magnesium.
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A monohydrate has been prepared by heating the tetrahydrate above 111° C. in hydrogen chloride, and a dihydrate has been obtained as small,white, deliquescent crystals from a solution of the chloride in hydrochloric acid.
The hexahydrate is obtained as a by-product in the preparation of potassium chloride from carnallite, in the Weldon process, and in the Solvay alkali process.
Concentrated solutions of magnesium chloride dissolve oxide or carbonate of lead, lead sulphate, and small amounts of zinc oxide.
One hundred parts of water dissolve 52.2 parts of MgCl2 at 0° C., and the density of the saturated solution at 15° C. is 1.3619.
The solubility of MgCl2.6H2O in parts of MgCl2 per 100 parts solution is -
| Temperature, ° C | 22 | 62 | 68.2 | 79.7 | <116.67/td> |
| Solution. | 35.5 | 38.0 | 38.3 | 39.5 | 46.1 |
MgCl2 and MgCl2.6H2O are soluble in alcohol.
[Mg] + (Cl2) = [MgCl2] + 151.01 Cal.
[MgCl2]+Aq. = MgCl2.Aq.+35.92 Cal.
[MgCl2.6H2O]+Aq. = MgCl2.Aq. +2.937 Cal.
Basic Chlorides of Magnesium
Magnesium chloride has a corrosive action on steam boilers, and when its solution is evaporated it begins to give off hydrogen chloride when the MgCl2 and H2O are in about the proportion of 1 molecule to 6.
Sorel found that a mixture of calcined magnesia with concentrated magnesium chloride solution set in a few hours to a solid mass. Magnesia or Sorel cements are now prepared by heating slightly burned dolomite with solutions of magnesium chloride. Gelatinous liquids, such as glue solutions, are added to secure effective mixing. Magnesia cements are useful for cementing metallic objects, but the atmosphere acts upon them.
Various compounds corresponding to the general formula MgCl2. xMgO.yH2O have been described. These magnesium oxychlorides are probably solid solutions and not definite compounds. According to Robinson and Waggaman, the solid substance in equilibrium with solutions containing less than 10 per cent, of MgCl2 is an indefinite solid solution, and MgCl2.3MgO.10H2O is the solid in contact with more concentrated solutions.
The compact products of the action of magnesium chloride on the oxide will polish. They absorb carbon dioxide, and water dissolves magnesium chloride out of them. The crystallised preparations are also attacked by water. Prolonged treatment with water leaves a compact solid as hard as sandstone, which will polish. This residue is a hydrated magnesium oxide, 2MgO.3H2O, and resembles the mineral brucite, Mg(OH)2.
Sorel found that a mixture of calcined magnesia with concentrated magnesium chloride solution set in a few hours to a solid mass. Magnesia or Sorel cements are now prepared by heating slightly burned dolomite with solutions of magnesium chloride. Gelatinous liquids, such as glue solutions, are added to secure effective mixing. Magnesia cements are useful for cementing metallic objects, but the atmosphere acts upon them.
Various compounds corresponding to the general formula MgCl2. xMgO.yH2O have been described. These magnesium oxychlorides are probably solid solutions and not definite compounds. According to Robinson and Waggaman, the solid substance in equilibrium with solutions containing less than 10 per cent, of MgCl2 is an indefinite solid solution, and MgCl2.3MgO.10H2O is the solid in contact with more concentrated solutions.
The compact products of the action of magnesium chloride on the oxide will polish. They absorb carbon dioxide, and water dissolves magnesium chloride out of them. The crystallised preparations are also attacked by water. Prolonged treatment with water leaves a compact solid as hard as sandstone, which will polish. This residue is a hydrated magnesium oxide, 2MgO.3H2O, and resembles the mineral brucite, Mg(OH)2.
Double Chlorides of Magnesium
A double chloride of sodium and magnesium, namely, NaCl.MgCl2, is indicated on the freezing-point curve, and is said to have been prepared crystalline. The potassium salts, KCl.MgCl2 and 2KCl.MgCl2, are indicated on the freezing-point curve. On raising a cool solution of potassium and magnesium chlorides to - 21° C., carnallite, KCl.MgCl2.6H2O, which is unstable at lower temperatures, is formed according to the equation -
KCl+MgCl2.12H2O ⇔ KCl.MgCl2.6H2O+6H2O.
Above 167.5° C. the carnallite is again completely decomposed, and at all intermediate temperatures it is partially decomposed by water. At these intermediate temperatures carnallite can only exist in contact with a solution containing excess of potassium or magnesium chloride.
Carnallite is concentrated commercially until the bulk of the potassium chloride is deposited. Magnesium chloride is obtained from the mother-liquor and used for preparing other magnesium salts.
Carnallite occurs at Stassfurt in large masses, which are usually tinged red with iron. It also occurs in some salt lakes.
Pure carnallite crystallises in colourless rhombic prisms which have a hardness of 1, a density of 1.6, and deliquesce in air, leaving a residue of solid potassium chloride. One hundred parts of water at 18° C. dissolve 64.5 parts of carnallite with lowering of temperature. Natural carnallite contains rubidium and caesium.
RbCl.MgCl2.6H2O and CsCl.MgCl2.6H2O have been described. Ammonium magnesium chloride, NH4.MgCl2.6H2O, crystallises from a solution of its constituent salts in small, colourless, deliquescent crystals which dissolve in 6 parts of water and have a density of 1.456.
Smaller crystals deposit from a solution containing the sulphates of magnesium and ammonium together with magnesium chloride.
Magnesium chloride free from oxide is obtained by igniting the double chloride.
2MgCl2.CaCl2.12H2O crystallises, above 22° C., from a solution of its constituent salts in appropriate proportions. It occurs in the Stassfurt deposits as transparent deliquescent masses, which are frequently yellow, and is known as tachhydrite. It crystallises in the hexagonal rhombohedral system, and has a hardness of 2.5. At 15° C. the density of the mineral is 1.671, and of the artificial crystals prepared by reaction between the component salts 1.666.
MgCl2.ZnCl2.6H2O, MgCl2.CdCl2.12H2O, MgCl2.HgCl2.6H2O and MgCl2.3HgCl2.5H2O, MgCl2.2TlCl3.6H2O, 2MgCl2.PbCl2.13H2O, MgCl2.Mg(Cl,OH).2SbCl5.17H2O, and MgCl2.2MnCl2.12H2O have been described.
KCl+MgCl2.12H2O ⇔ KCl.MgCl2.6H2O+6H2O.
Above 167.5° C. the carnallite is again completely decomposed, and at all intermediate temperatures it is partially decomposed by water. At these intermediate temperatures carnallite can only exist in contact with a solution containing excess of potassium or magnesium chloride.
Carnallite is concentrated commercially until the bulk of the potassium chloride is deposited. Magnesium chloride is obtained from the mother-liquor and used for preparing other magnesium salts.
Carnallite occurs at Stassfurt in large masses, which are usually tinged red with iron. It also occurs in some salt lakes.
Pure carnallite crystallises in colourless rhombic prisms which have a hardness of 1, a density of 1.6, and deliquesce in air, leaving a residue of solid potassium chloride. One hundred parts of water at 18° C. dissolve 64.5 parts of carnallite with lowering of temperature. Natural carnallite contains rubidium and caesium.
RbCl.MgCl2.6H2O and CsCl.MgCl2.6H2O have been described. Ammonium magnesium chloride, NH4.MgCl2.6H2O, crystallises from a solution of its constituent salts in small, colourless, deliquescent crystals which dissolve in 6 parts of water and have a density of 1.456.
Smaller crystals deposit from a solution containing the sulphates of magnesium and ammonium together with magnesium chloride.
Magnesium chloride free from oxide is obtained by igniting the double chloride.
2MgCl2.CaCl2.12H2O crystallises, above 22° C., from a solution of its constituent salts in appropriate proportions. It occurs in the Stassfurt deposits as transparent deliquescent masses, which are frequently yellow, and is known as tachhydrite. It crystallises in the hexagonal rhombohedral system, and has a hardness of 2.5. At 15° C. the density of the mineral is 1.671, and of the artificial crystals prepared by reaction between the component salts 1.666.
MgCl2.ZnCl2.6H2O, MgCl2.CdCl2.12H2O, MgCl2.HgCl2.6H2O and MgCl2.3HgCl2.5H2O, MgCl2.2TlCl3.6H2O, 2MgCl2.PbCl2.13H2O, MgCl2.Mg(Cl,OH).2SbCl5.17H2O, and MgCl2.2MnCl2.12H2O have been described.
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