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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.
To clarify that it is the gaseous form that is being referred to, the term anhydrous is prefixed to the name of the substance: Gaseous ammonia is generally referred to as anhydrous ammonia, to distinguish it from its solution in water, household ammonia solution, also known as ammonium hydroxide.
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.
Anhydrous metal chlorides suitable for preparing other coordination compounds may be dehydrated by treatment with thionyl chloride: [1] [3] MCl n · x H 2 O + x SOCl 2 → MCl n + x SO 2 + 2 x HCl The silver and thallium(I) cations have a great affinity for halide anions in solution, and the metal halide quantitatively precipitates from aqueous ...
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)
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
The desired product, benzoic acid (3), is obtained by the following work-up: [2] Synthesis of benzoic acid with work-up step in red. The reaction mixture containing the Grignard reagent is allowed to warm to room temperature in a water bath to allow excess dry ice to evaporate. Any remaining Grignard reagent is quenched by the addition of water.
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.