| MadSci Network: Chemistry |
Sandra,
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.
References:
(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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