Grow crystals of chrome alum, a double saltĬontact with solutions of chromium(III) sulfate or inhalation of particles may cause irritation, but overall this compound is relatively non-toxic.Ĭhromium(III) sulfate is relatively stable and has low reactivity, but should be kept away from temperatures greater than 40 ☌ when in the presence of moisture to avoid complex formation.It should be noted, however, that many grades of chromium(III) oxide are not reactive enough, often as a result of being calcined, to respond to treatment with acid. To extract the chromium(III) from solution, the reaction products must be treated with bases to precipitate chromium(III) hydroxide.Ĭhromium(III) sulfate can be more directly produced by the action of cold, dilute sulfuric acid on chromium(III) hydroxide or chromium(III) oxide. If the temperature of the reaction is kept low enough, the presence of chromium(III) sulfate will be indicated by a blue or blue-violet color to the end product, rather than a green color produced when the temperature is too high. The interesting thing about this compound is that it contains a transition metal as its cation, i.e. The Jones oxidation, which uses a solution of potassium dichromate or sodium dichromate acidified with sulfuric acid to oxidize alcohols, produces chromium(III) sulfate as a byproduct, along with sodium or potassium sulfate. Cr2O3 Explanation: The first thing to notice here is that you're dealing with an ionic compound that contains chromium, Cr, a transition metal, and oxygen, O, a non-metal. Its use as a tanning chemical has largely been superseded by chrome alum and other agents. Purer samples can be dried to form a lighter-colored powder.Ĭhromium(III) sulfate is readily soluble in water and some lower alcohols.Ĭhromium sulfate, for the most part, can only be purchased from online suppliers. Recently prepared samples or those that have been subjected to heat may contain a deep green-colored sulfato complex and are hygroscopic as a result. Strong oxidizers such as hypochlorite can oxidise the aqueous Cr(III) to chromate (CrO 4 2-).Ĭhromium(III) sulfate most often appears as a blue-grey or violet-grey amorphous solid. If the base used is a carbonate or bicarbonate, this reaction is accompanied with the release of carbon dioxide, in a manner similar to iron, which does not form carbonates. Treatment of chromium(III) sulfate with bases produces chromium(III) hydroxide.
Freshly prepared chromium sulfate often contains traces of this coloration, with some samples even appearing green rather than blue, but is otherwise usable.Ī solution of both chromium(III) sulfate and potassium sulfate will yield crystals of chrome alum on partial evaporation. Sol :- The valency of Cr in chromium (III) 3 And The val. Solutions of chromium(III) sulfate turn from blue to green upon heating, indicating the formation of a less reactive "sulfato-complex" that may take days or weeks to revert.
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