Arsenic trioxide is a white solid. It dissolves in water to make an acidic solution of arsenious acid. It dissolves easily in bases to make arsenites. It reacts with concentrated hydrochloric acid to make arsenic trichloride. It reacts with very strong oxidizing agents to make arsenic pentoxide. It reacts with reducing agents to make arsenic or arsine. It sublimes much easier than metal oxides, making it easy to separate by heating the mixture.