Indium hydroxide, In(OH)₃

Indium is slowly converted by air and moisture into Indium hydroxide, In(OH)₃. The hydroxide may be prepared by adding ammonia to an aqueous solution of an indium salt and washing the precipitate. Other precipitants may be used instead of ammonia, e.g. potassium nitrite, hydroxylamine, and the simple aliphatic primary and secondary amines. The air-dried precipitate has the composition 2In(OH)₃.3H₂O, and loses 3H₂O at 100°.

Freshly precipitated indium hydroxide exhibits a marked tendency to pass into the colloidal state in the absence of electrolytes. It is slightly soluble in concentrated ammonium hydroxide, and dissolves readily in alkali hydroxides. From the latter solutions it is reprecipitated on boiling or standing. When heated to redness, it leaves indium sesqui-oxide. With dilute acids it reacts to produce indium salts and water; but it possesses slight acidic properties, a magnesium indate being known. This substance, of the formula MgIn₂O₄.3H₂O, is obtained as a white precipitate when aqueous solutions of magnesium and indium chlorides are mixed and boiled.