The homovalent oxides of non-metals in inorganic acids are the anhydrides of oxyacids. For example, if the valence of carbon in carbonic acid is +4, then its anhydride is carbon dioxide.
Organic acids can be used to remove water, which is to add a stoichiometric number in front of the acid to match the hydrogen ion to an even number (the original even number is not necessary) and then remove one or several H2O. For example: CH3COOH (the numbers are subscripts, the same below) has only 1 hydrogen ion in front of the stoichiometric number 2, and then remove one H2O, the obtained (CH3CO)2O is its acid anhydride; the same thing, if there is For 3 hydrogen ions, add a stoichiometric number of 2, and then remove 3 water.
Alumina is produced by dehydration of Al(OH)3, because aluminum hydroxide can be written as HAlO2·H2O (metaluminate), and dehydrated is alumina {2HAlO2·H2O= Al2O3·2H2O (dehydration)→Al2O3}.