Neutralization Reactions

Acids and bases have been known and studied since alchemist first tried to turn lead into gold.  Both are widely used in industry.  The chemistry of acids and bases is essential to understanding the environmental phenomenon of acid rain. There are several different chemical definintions of acids and bases but for the purposes of this discussion acids are defined as chemical substances that contains hydrogen that dissociates in water to form H₃O⁺ (hydronium ions).  For a listing of common acids and bases go to the Naming of Acids and Bases page in the Nomeclature Unit of this course.
 
 

The hydronium ion is also referred to as the hydrogen ion. They are represented as H+, since a hydrogen ion in an aqueous environment becomes a hydronium ion.                                H+(aq)  + H2O (l)  H30+(aq) Bases are substances that contain an OH group and that dissociates in water to release hydroxide ions (OH-).  When strong acids and bases come together they react so as to neutralize their acid and base properties producing water and a salt. Some energy as heat can also be produced.  A net ionic equation is an equation that shows only the reactants ions that undergo a change during the reaction.  For all acid and base neutralizations the net ionic equation is essentially the same.                                 H+(aq) + OH-(aq)  H2O(l) Since the ions, like the sodium and chloride ions, (highlighted in the full neutralization equation above), remain in solution as ions, they have not changed.  Ions that remain unchanged during a chemical reaction are referred to as spectator ions Weak acids and bases do not dissociate completely in water and so release fewer  H3O+ or OH-. The strength of acids and bases is measured on a pH where:                                 pH = -log[H+ ],  The squared brackets indicate the concentration of whatever substances is named between them.   As a result of this equation, the higher the hydrogen ion concentration is, the lower the pH will be.  Substances with very low pH's are acids.  If the H+ concentration is very low, the pH will be high. Substances with high pH values are bases. The acid-base nature of water is an important component of acid-base chemistry.  Water actually behaves both as an acid and as a base.  Water obviously contains both H+ ions and OH- ions.  At equilibrium, the concentration of H+ in water is 10-7 moles/liter, so we can calculate the pH of pure water as:                                 pH = -log[H+] = -log(10-7) = 7 Solutions with a pH of 7 are said to be neutral. Substances with pH values below 7 are acidic, while those above a pH of 7 are basic.  In the atmospheric sciences, the acidity of rain water is of great interest.  Natural unpolluted rainwater is slightly acidic.  It actually has a pH of about 5.7.  This is due to the absorption of carbon dioxide, readily available in the atmosphere, to form carbonic acid, H2CO3.