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Author: Subject: How to crystalise Aluminium chloride hexahydrate
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[*] posted on 27-3-2020 at 23:16
How to crystalise Aluminium chloride hexahydrate

I have made some aluminium chloride with some aluminium powder and Concentrated HCl. whats the best method to crystallise and obtain the solid product from it. Will heating upto crystallisation point and cooling it down produce crystals? I heard aluminium chloride would form oxides then? So whats the best method

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Chemi Pharma
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[*] posted on 28-3-2020 at 09:08

A solution of aluminum chloride can be prepared directly by the action of hydrochloric acid on the aluminum, but if this solution is evaporated to dryness, the solid that is left is the aluminum oxide instead of the aluminum chloride. Hydrolysis is prevented by hydrochloric acid, and the aluminum chloride hexahydrate can be crystallized from an hydrochloric acid solution. The solution of aluminum chloride is saturated with hydrogen chloride, which not only drives back hydrolysis but also reduces the solubility of the aluminum chloride hexahydrate.

13.5 g of aluminum turnings are placed in a 500 ml flask containing 50 ml of water. To this flask, 125 ml of concentrated hydrochloric acid are added dropwise until a vigorous reaction has started and finally as rapidly as may be without producing too violent a reaction. The 125 ml of concentrated hydrochloric acid should just suffice to dissolve the aluminum turnings. Unless it is perfectly clear, the solution is filtered, the filtrate is returned to the 500 ml flask. To prevent hydrolysis of aluminum chloride the hydrogen chloride gas is pass into the flask containing the aluminum chloride solution. The end of the delivery for gaseous hydrogen chloride tube dipping into the solution must be at least 1.5 cm in diameter, else it will become stopped with the precipitated aluminum chloride hexahydrate. The flask containing aluminum chloride hexahydrate solution is further fitted with an exit tube which will lead any excess of hydrogen chloride gas to within few centimeters of the surface of water in a bottle. The flask with the solution of aluminum chloride is immersed in the ice-water bath, and hydrogen chloride gas is passed into the solution until it is saturated. The crystalline precipitate of aluminum chloride hexahydrate are collected in a funnel and dried as completely as possible with suction while pressing the crystal mass with a glass stopper. The aluminum chloride hexahydrate is additionally dried in the desiccator over solid sodium hydroxide for several days to completely remove the excess of hydrochloric acid.

Synthetic inorganic chemistry, by A. A. Blanchard, 212-213, 1936
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