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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.
Water can sometimes be removed by heat, vacuum, or the presence of anhydrous hydrohalic acid. Anhydrous metal chlorides suitable for preparing other coordination compounds may be dehydrated by treatment with thionyl chloride: [1] [3] MCl n ·xH 2 O + x SOCl 2 → MCl n + x SO 2 + 2x HCl
If water molecules become suspended among the substance's molecules, adsorbing substances can become physically changed, e.g. changing in volume, boiling point, viscosity or some other physical characteristic or property of the substance. For example, a finely dispersed hygroscopic powder, such as a salt, may become clumpy over time due to ...
Typically anhydrous solvents will contain approximately 10 ppm of water and will increase in wetness if they are not properly stored. Organic solutions can be dried using a range of drying agents . Typically following a workup the organic extract is dried using magnesium sulfate or a similar drying agent to remove most remaining water.
A salt containing reactive cations undergo hydrolysis by which they react with water molecules, causing deprotonation of the conjugate acids. For example, the acid salt ammonium chloride is the main species formed upon the half neutralization of ammonia in aqueous solution of hydrogen chloride: [2] NH 3 + HCl(aq) → [NH 4] + Cl − (aq)
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.
Both compound classes are hydrophobic and therefore virtually insoluble in water - the solubility of the commonly used iso-octadecenylsuccinic anhydride (C 18-ASA) is only 5.33x10 −5 mgl −1. ASA are less hydrophobic and thus less water repellent than AKD because of their shorter chain length.
Many organic molecules, as well as inorganic molecules, form crystals that incorporate water into the crystalline structure without chemical alteration of the organic molecule (water of crystallization). The sugar trehalose, for example, exists in both an anhydrous form (melting point 203 °C) and as a dihydrate (melting point 97 °C).