Alkaline oxide refers to an oxide that dissolves in water to form a base or reacts with an acid to form a salt and water. At high temperatures, some alkaline oxides and acidic oxides react to form salts.

Reaction of basic oxides and acidic oxides

At high temperatures, some basic oxides and acidic oxides react to form salts: CaO+SiO 2 =CaSiO 3 .

Some basic oxides can react directly with acidic oxides: Na 2 O+CO 2 =Na 2 CO 3 . Relevant reactions between alkaline oxides and acidic oxides

(1) Alkaline oxide + acid = salt + water: Fe 2 O 3 +6HCl = 2FeCl 3 +3H 2 O; CuO + H 2 SO 4 =CuSO 4 +H 2 O.

(2) Acidic oxide + alkali = salt + water: 2NaOH+CO 2 =Na 2 CO 3 +H 2 O; 2NaOH+SiO 2 =Na 2 SiO 3 +H 2 O.

(3) Alkaline oxides react with water to generate the corresponding hydroxides: Na 2 O + H 2 O = 2NaOH; CaO + H 2 O = Ca(OH) 2 .

(4) Most acidic oxides can directly combine with water to form oxygen-containing acids: SO 3 +H 2 O = H 2 SO 4 ; SO 2 +H 2 O = (reversible) H 2 SO 3.