The statement "acid anhydrides are acidic oxides" is accurate within a specific context. Acid anhydrides are formed through the dehydration of acids, whereas acidic oxides are oxides that react with bases to produce salts and water; conceptually, therefore, the two are not strictly equivalent. In inorganic chemistry, acid anhydrides are indeed formed by the dehydration of acids-and the vast majority of them happen to be oxides-so in this realm, the two terms can be treated as equivalent. However, in organic chemistry, the dehydration products of many organic acids are not oxides; for instance, acetic acid (CH₃COOH) dehydrates to form acetic anhydride ((CH₃CO)₂O), which, by definition, cannot be classified as an acidic oxide.
Acid Anhydrides of Common Acids:
- H₂SO₄ → SO₃
- H₂SO₃ → SO₂
- H₂CO₃ → CO₂
- H₃PO₄ → P₂O₅
- HNO₃ → N₂O₅
- HNO₂ → N₂O₃
- CH₃COOH → (CH₃CO)₂O
- H₃PO₃ → P₂O₃
