Acids and bases play a central role in chemistry because, with the
exception of
redox reactions, every chemical reaction can be classified as an
acid-base reaction. Our understanding of chemical reactions as acid-base
interactions comes from the wide acceptance of the Lewis
definition of acids and bases, which supplanted both the earlier Bronsted-Lowry concept and the
first definition--the
Arrhenius model. Arrhenius first defined acids as proton (H+)
producers in
aqueous solution and bases as hydroxide (OH-) producers.
Although this model is intuitively correct, it is limited to substances that
include proton and hydroxide groups. Bronsted and Lowry
proposed the more general
definitions of acids and bases as proton donors and acceptors, respectively.
Unlike the Arrhenius
conception, the Bronsted-Lowry model accounts for acids in solvents
other than water, where the proton transfers do not necessarily involve
hydroxide ions. But the Bronsted-Lowry model fails to explain the observation
that metal ions make water more acidic (discussed in
Calculating pH's). Finally, Lewis gave us the
more general
definition of acids and
bases that we use today. According to Lewis, acids are electron
pair acceptors and
bases are electron pair donors. Any chemical reaction that can be represented
as a simple exchange of valence electron
pairs to break and form bonds is therefore an acid-base reaction.
Acid-base chemistry is important to us on a practical level as well, outside of
laboratory chemical reactions. Our bodily functions, ranging from the
microscopic transport of ions across nerve cell membranes to the macroscopic
acidic digestion of food in the stomach, are all ruled by the principles of
acid-base chemistry. Homeostasis, the temperature and chemical balances in our
bodies, is maintained by acid-base reactions. For example, fluctuations in the
pH, or concentration of hydrogen ions, of our blood is moderated at a
comfortable level through use of buffers. Learning how buffers work and
what their limitations are can help us to better understand our physiology. We
will start by introducing fundamentals of acid-base chemistry and the
calculation of pH, and then we will cover techniques for measuring pH. We learn
about buffers and see how they are applied to measure the acidic content of
solutions through titration.
