For example, take a look at the equation for hydrochloric acid.
HCl(aq) → H+(aq) + Cl–(aq)
Note that (aq) stands for aqueous and means that the substance is in solution.
Acids are often produced from non-metal oxides. For example, sulfur oxides make sulfuric acid.
When alkalis dissolve in water they produce hydroxide ions, OH–.
For example, take a look at the equation for sodium hydroxide.
NaOH(aq) → Na+(aq) + OH–(aq)
Ammonia is slightly different. This is the equation for ammonia in solution.
NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq)
A base is chemically opposite to an acid. Some bases dissolve in water and are called alkalis. Other bases, including many metal oxides, do not dissolve in water.
When the H+ ions from an acid react with the OH– ions from an alkali, a neutralisation reaction occurs to form water. This is the equation for the reaction.
H+(aq) + OH–(aq) → H2O(l)
For example, hydrochloric acid and sodium hydroxide solution react together to form water and sodium chloride solution. The acid contains H+ ions and Cl– ions, and the alkali contains Na+ ions and OH– ions. The H+ ions and OH– ions produce the water, and the Na+ ions and Cl– ions produce the sodium chloride, NaCl(aq).
Because neutralisation reactions involve the loss and gain of hydrogen ions, this process is sometimes referred to as ‘proton transfer’.