Anhydride

In inorganic chemistry, an acid anhydride can refer to an acidic oxide, i.e., an oxide that reacts with water to form an oxyacid (an inorganic acid that contains oxygen or carbonic acid), or with a base to form a salt. For example, dinitrogen trioxide is the anhydride of nitrous acid. Similarly, dinitrogen pentoxide is the anhydride of nitric acid: