Both of these are combination reactions, and both can be reversed by heating the products. Metal hydroxides decompose on heating to give the metal oxide and water, and oxyacids decompose on heating to give water and the nonmetal oxide in the appropriate oxidation state. Reaction of an acid with a base gives a salt plus water . The base may be a metal hydroxide, a metal oxide, or a weak base such as NH 3 . The oxidation states of the anion of the acid and cation of the base normally remain unchanged.
Ammonium salts react with metal hydroxides and oxides in an acid-base reaction to produce ammonia .
Either or both of the reactants may be a pure material or in aqueous solution. The original salt of the weak acid may be either a pure solid or in aqueous solution. The best-known examples of this type of reaction involve carbonates, bicarbonates, sulfides, and sulfites, but many other examples are known as well. Normally, these reactions do not involve oxidation or reduction. Whether or not a precipitate forms depends on the exact combination of salts used.