Auric hydroxide

Gold-hydroxyd, n. gold hydroxide, specif, auric hydroxide, gold(III) hydroxide, -jodid, n. gold iodide, specif, auric iodide, gold(III) iodide, -jodiir, n. aurous iodide, gold (I) iodide, -kafer, m. gold beetle. 

Formula Au(OH)3 MW 247.99 Synonyms gold trihydroxide auric hydroxide. 

In aqueous solution the salts of the metals of Group I. must be classed as strong electrolytes, a statement also applicable to the hydroxides of the univalent cations, except aurous hydroxide, AuOH. This hydroxide shares with cupric hydroxide and auric hydroxide a weak basic character, solutions of their salts having an acidic reaction, due to hydrolytic dissociation. 

Auric hydroxide, AuOOH.—A 5 per cent, yield of the pure hydroxide is obtained by precipitating auric chloride with basic magnesium carbonate, and treating the precipitate with 30 per cent, nitric acid, most of the auric hydroxide dissolving in this solvent.4 The poor yield is probably explicable on the assumption of the formation of insoluble complex salts which are precipitated with the hydroxide, and render necessary the drastic process of treatment with nitric acid, thus dissolving a large proportion of the hydroxide itself. The hydroxide has also been prepared in an impure state by several other methods.6... 

In the pure condition auric hydroxide resembles ferric hydroxide in appearance, and has the colour of brown ochre, but impurities impart to it a yellowish or greenish tint. It is soluble in nitric acid and hydrochloric acid, and in hot potassium-hydroxide solution, but insoluble in solutions of the carbonates of the alkali-metals and ammonium.6 It dissolves in solutions of the chlorides of sodium, potassium, and barium with production of complex salts.7 Prolonged heating at 140° to ISO0 C. eliminates all its water, with formation of auric oxide, Au2Oa. At 155° to 165° C. auric oxide is converted into gold monoxide, AuO.8... 

Auric hydroxide behaves as a very weak add having the anion AuOa. Evaporation of its solution in aqueous potassium hydroxide yields yellow needles of potassium aurate, KAu02,3H20.9 In accordance with the weak nature of the acid, the solution of this salt in water is strongly alkaline. 

Acid auryl sulphate, AuOHS04.—This sulphate is produced by the action of concentrated sulphuric acid on auric hydroxide at 180° C., the brown, basic salt formed being converted by heating at 200° C. into the yellow acid auryl sulphate.12 It is decomposed by water with formation of auric hydroxide, but dissolves in concentrated sulphuric acid to a yellowish-red solution, from which it separates unchanged. When this acid solution is heated with potassium hydrogen sulphate, a yellow, crystalline salt of the formula KAu(S04)2 separates. It is more stable than acid auryl sulphate, but is slowly decomposed by water, with... 

Dimethyl auric hydroxide, [(CH3)2AuOH] 4 is also a cyclic tetramer, (e), but there is apparently a strange asymmetry and the interbond angles at Au(iii) range from 81 to 106° the range of Au-0 bond lengths, l 87-2-40 A, is inexplicably large. ... 

Auric hydroxide is reacted with warm cone. KOH in the absence of atmospheric COg. After filtration the solution is allowed to evaporate in the dark. The precipitated crystals are dried in vacuum over HgSO. ... 

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