Antimony pentoxide, also known as antimony anhydride, is an inorganic compound with the chemical formula Sb2O5. It is a white or yellow powder that is insoluble in water but soluble in hot hydrochloric acid. It is primarily used as a high-efficiency flame retardant synergist for chemical fiber fabrics, plastics, paper, rubber, and copper-clad laminates. It is also used in the manufacture of antimonates and antimony compounds, as well as in the pharmaceutical industry.

Density: 3.78 g/cm3

Melting Point: 380°C (decomposition)

Appearance: White or yellow powder

Solubility: Insoluble in water, soluble in hot hydrochloric acid

Stability: Loses oxygen at 380°C to form antimony tetroxide, and at 930°C to form antimony trioxide. It dissolves in strong bases to form antimonates. It has low toxicity. Although insoluble in water, it forms a colloidal solution when hydrated. It is soluble in hydrochloric acid and aqueous potassium hydroxide solutions. Sb2O5 is reduced with sulfur dioxide to form Sb2O3. Chemical Properties: Antimony pentoxide is dissolved in alkali metal hydroxide or co-melted with its solid to produce antimony salts M[Sb(OH)6]. These alkali metal antimonates MSb(OH)6 exchange with acidic ion resins to produce "antimonic acid," which exhibits a strong acid-like titration curve with a pK value of 2.5.