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Anhydrous aluminium chloride is hygroscopic, having a very pronounced affinity for water. It fumes in moist air and hisses when mixed with liquid water as the Cl − ligands are displaced with H 2 O molecules to form the hexahydrate [Al(H 2 O) 6]Cl 3. The anhydrous phase cannot be regained on heating the hexahydrate.
The strength of the bonds between the metal ion and water molecules in the primary solvation shell increases with the electrical charge, z, on the metal ion and decreases as its ionic radius, r, increases. Aqua ions are subject to hydrolysis. The logarithm of the first hydrolysis constant is proportional to z 2 /r for most aqua ions.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The water content of most compounds can be determined with a knowledge of its formula. An unknown sample can be determined through thermogravimetric analysis (TGA) where the sample is heated strongly, and the accurate weight of a sample is plotted against the temperature.
To prevent this, anhydrous solvents must be used when performing certain reactions. Examples of reactions requiring the use of anhydrous solvents are the Grignard reaction and the Wurtz reaction. Solvents have typically been dried using distillation or by reaction with reactive metals or metal hydrides. These methods can be dangerous and are a ...
Some low-oxidation state transition metals have halides which dissolve well in water, such as ferrous chloride, nickelous chloride, and cupric chloride. Metal cations with a high oxidation state tend to undergo hydrolysis instead, e.g. ferric chloride, aluminium chloride, and titanium tetrachloride. [1]
For similar reasons, anhydrous aluminium salts cannot be made by heating their "hydrates": hydrated aluminium chloride is in fact not AlCl 3 ·6H 2 O but [Al(H 2 O) 6]Cl 3, and the Al–O bonds are so strong that heating is not sufficient to break them and form Al–Cl bonds instead: [2] 2[Al(H 2 O) 6]Cl 3 Al 2 O 3 + 6 HCl + 9 H 2 O
[1] [2] As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified. [3] [4] A non-aqueous solution is a solution in which the solvent is a liquid, but is ...