In industry it is produced by the precipitation of chromium sulphate with solutions of sodium hydroxide or ammonium hydroxide. Synthesis of chromium hydroxide in the industrial field Thus, both the acidic and the basic medium are capable of dissolving the chromium hydroxide. This negative complex is associated with the surrounding cations (Na +, if the base is NaOH), and after the evaporation of the water the sodium chromite salt precipitates (NaCrO 2, emerald green). When all the Cr (OH 2 ) 3 (OH) 3 Once it has reacted, a final complex is obtained as indicated by the chemical equation:Ĭr (OH 2 ) 3 (OH) 3 + 3 OH - 3- + 3 H 2 OR This complex makes the solution a light green color, which intensifies as the reaction proceeds. On the other hand, when more base is added, the OH - they continue replacing the water molecules, forming the negative complex. When reacting with acids, Cr (OH 2 ) 3 (OH) 3 it dissolves because the hydroxyl bridges break down, responsible for the gelatinous appearance of the precipitate. This property is characteristic of Cr 3+. Why is chromium hydroxide soluble in acidic and basic solutions? The reason is due to its amphoteric character, which allows it to react with both acids and bases. In addition, when heated, it decomposes, producing vapors of chromium oxide. It is insoluble in water, but soluble in strong acids and bases. The Cr (OH) 3 It has the appearance of a blue-green powder, but when it comes into contact with the water it forms a gelatinous gray-green precipitate. However, it is the physicochemical studies of the solid that can shed light on the true structure of Cr (OH) 3 in this point. 3H 2 OR in other words, the tri-hydrated chromic oxide.When the Cr (OH 2 ) 3 (OH) 3 it dehydrates, the water coordinated with the Cr is eliminated 3+, and since this cation is coordinated with six species (ligands), polymeric structures arise in which Cr-Cr bonds may be involved.Īlso, when dehydrated, its structure can be considered Cr type 2 OR 3 In fact, this"gray-green jelly"refuses to rush orderly.įinally, the Cr (OH 2 ) 3 (OH) 3 consists of an octahedron with the Cr 3+ in the center, and linked to three water molecules and three OH - that neutralize its positive charge this without considering the polymerization. Consecutively, this new complex dehydrates another aqueous complex, creating dimers bound by hydroxide bridges:Īs the basicity of the medium increases (the pH rises) the complex is formed +, and also increase the likelihood of new hydroxide bridges to create gelatinous polymers. When NaOH (or KOH) is added to the reaction medium, the OH ion - deprotonates a molecule of this complex, forming 2+ (Now there are five molecules of water because the sixth lost a proton). Cl ions - they can come, for example, from hydrochloric acid if it has been used for the dissolution of salt or chromic oxide. In the upper image, the structure of the complex 3+. For example, the complex 3+ indicates that the metallic center of chromium is coordinated with six water molecules Since these are neutral, the complex exhibits the positive charge of the original cation, Cr 3+. However, the nature of the Cr-OH bond is more covalent, due to the coordination chemistry of the Cr 3+. Likewise and assuming the purely ionic character of their interactions, in the solid Cr cations can be visualized 3+ interacting with a tripled amount of OH anions. The upper image is the simplest representation of Cr (OH) 3 in gaseous phase and isolated. 3 Synthesis of chromium hydroxide in the industrial field.
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