The reaction of an acid and a base is called a neutralization reaction. Although acids and bases have their own unique chemistries, the acid and base cancel each other’s chemistry to produce a rather innocuous substance – water.
In fact, the general reaction between an acid and a base is
acid + base → water + salt
where the term salt is generally used to define any ionic compound (soluble or insoluble) that is formed from a reaction between an acid and a base.
For example, the balanced chemical equation for the reaction between HCl(aq) and KOH(aq) is
HCl(aq) + KOH(aq) → H2O(ℓ) + KCl(aq)
where the salt is KCl.
By counting the number of atoms of each element, we find that only one water molecule is formed as a product.
However, in the reaction between HCl(aq) and Mg(OH)2(aq), additional molecules of HCl and H2O are required to balance the chemical equation:
2HCl(aq) + Mg(OH)2(aq) → 2H2O(ℓ) + MgCl2(aq)
Here, the salt is MgCl2. (This is one of several reactions that take place when a type of antacid – a base – is used to treat stomach acid.)