Acid Anhydrides

In-depth explanation of Acid Anhydrides

Acid anhydrides are oxides of nonmetals that react with water to form acids. Carbon dioxide gives carbonic acid, sulfur trioxide gives sulfuric acid and dinitrogen pentoxide gives nitric acid. These oxides are typically covalent and molecular, and they dissolve in alkaline solutions to form salts. Their reactions with water are the source of many acidic pollutants and industrial acids. They illustrate how the acidity of an element's oxide relates to its position in the periodic table.

Going deeper: Acid Anhydrides

Key ideas: Acidic oxides (mostly nonmetal oxides) react with water to give acids or react with bases to give salts: CO2 + H2O gives H2CO3, SO3 + H2O gives H2SO4, N2O5 gives HNO3, P4O10 gives H3PO4, Cl2O7 gives HClO4. Oxidation number of the element stays the same in the acid. In organic chemistry, acetic anhydride reacts with water giving two acetic acids.

Common mistakes and connections: Mistakes: assuming all nonmetal oxides are acidic (CO, NO and N2O are neutral), and mixing up SO2 (gives H2SO3) with SO3 (gives H2SO4). Higher oxidation states give stronger acids. These oxides are responsible for acid rain, linking to environmental chemistry. Compare with basic anhydrides.

Visualization of Acid Anhydrides

CO2 is the anhydride of carbonic acid: it reacts with water to give H2CO3, which is why non-metal oxides generally form acidic solutions. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Sulfur dioxide dissolved in rainwater forms sulfurous acid, one of the acidic components of acid rain.

Where Acid Anhydrides fits in Acids, Bases & Electrochemistry

Acid Anhydrides is topic 102 of 105 in Acids, Bases & Electrochemistry.

Related topics

• Nonaqueous Acids and BasesAdvanced
• SuperacidsAdvanced
• Hard and Soft Acids and BasesAdvanced
• Basic AnhydridesIntermediate
• Water HardnessIntermediate
• AlkalinityAdvanced

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