It forms crystallizable salts with potassium and calcium hydrates, and functions as a weak acid forming salts named plumbates.
The element is insoluble in water, but dissolves in concentrated sulphuric acid forming a deep red solution.
Chromium sesquioxide is a basic oxide, although like alumina it acts as an acid-forming oxide towards strong bases, forming salts called chromites.
For salts of this acid-forming oxide and for perchromic acid see Bichromates.
Cuprous oxide is reduced by hydrogen, carbon monoxide, charcoal, or iron, to the metal; it dissolves in hydrochloric acid forming cuprous chloride, and in other mineral acids to form cupric salts, with the separation of copper.