antimony(III) oxide (antimony trioxide)

Antimony trioxide with the formula Sb₂O₃, molecula weight 291.518 g/mol , density 5.2 g/cm3 , melting point 656 °C . 
Antimony trioxide is a white insoluble solid. It is an amphoteric oxide with a strong tendency to act as a base. It can be prepared by direct oxidation by air, oxygen, or steam and is formed when antimony(III) chloride is hydrolyzed by excess boiling water.