|MadSci Network: Chemistry|
Various substances exhibit similar characteristics in how they react with other substances. A broad range of these characteristics has been divided into the two categories, acid and base, where the pH measurement is related to a ratio of the base components to the acid components. If a substance has one acid component for each base component, it is said to be neutral and has a pH value of 7. Greater than 7 is less acid, more base, and less than 7 is more acid and less base. Each unit is 10 times the previous, i.e., a pH of 9 is 10 times more base than 8, a pH of 5 is 10 times more acid than 6. Some examples of more acid like things are vinegar, orange juice, and the liquid in your car battery ( pH of battery acid = 1 ! So don't touch it !) and stomach acid (pH = 1). Though stomach acid has a pH of 1 there are strong linings inside the stomach that protects it from burning up. Bases include lye, drain cleaner (pH = 13 ! Don't touch it either!!), and baking soda. When acid like substances are mixed with base like substances, they react with each other producing some by-products and leaving the resulting solution with a pH somewhere between the two original values. The further apart the pH of the two substances, the more energy is released in the reaction.
If you mix something of pH = 1 with another solution of pH = 14, you will get a vigorous reaction with release of tremendous amount of energy. This is an example of an exothermic reaction. For example a suitable high concentration of HCl (hydrochloric acid ) may have a pH of 1 and a high concentration of sodium hydroxide (NaOH) may have a pH of close to 13-14. When you mix these together, you will get the formation of NaCl and water with a release of large amounts of heat according to the reaction
HCl + NaOH -> NaCl + H2O
If you use another pair of acid and base you will end up with a different reaction. In all cases you will get salt and water as products.
(1) P.W. Atkins, Physical Chemistry, W.H. Freeman & Co., NY, 1990
(2) http://explorer.scrtec.org/explorer/explorer-db/rsrc/783749730- 447DED81.2.PDF
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