Acid/Base
chemistry is based on the concept of chemical equilibrium. Chemical equilibrium
is defined as: A state of dynamic balance in which the rate of formation of the
of the products of a reaction from the reactants equals the rate of formation
of the reactants from the products; at equilibrium the concentrations of the reactants
and products remains constant.�This ties into acids and bases because how much
it takes to neutralize each other is an equilibrium problem.
There are three main ways to define acids and bases.
One way is the Arrhenius definition. An Arrhenius acid is a substance that releases
H+ ions and an Arrhenius base is a substance that releases OH- ions.This definition
is weak because there are many acids and bases that do not directly release a
hydronium or hydroxide ion, for example the weak base ammonia (NH3).So if ammonia
does not directly donate a hydroxide ion to the solution, then why is it still
considered a base? The Arrhenius definition of a base does not seem to fit the
substance, so we must look at another definition of an acid and a base.�The Br�nstead-Lowry
definition is that an acid is a proton donor and a base is a proton acceptor.
This better describes what happens to ammonia when it is dissolved in water. Ammonia
accepts a proton from water to turn in to the ammoniumion (NH4+) and water turns
into the hydroxide ion. This accounts for an ammonia solution being basic. Another
more general way to define acids and bases is saying that acids are electron pair
acceptors and bases are electron pair donors.�These are called Lewis acids and
bases.
How much an acid or a base dissociates in solution
correlates with its strength.� Strong acids and bases, such as HCl and NaOH, dissociate
100% in solution meaning that these substances completely ionize and are strong
electrolytes.�Weak acids and bases, such as acetic acid or ammonia, only partially
dissociate in solution.�This is where the concept of equilibrium comes onto play.�The
concentrations of each ion in solution can be calculated then plugged into the
mass-action expression and the equilibrium constant can be found. Vice versa,
with a known equilibrium constant, concentrations at equilibrium of every substance
can be found.�The most common way this is done is through a process called titration.�This
is where an acid or base is titrated by a base or an acid to the point where the
solution changes its pH.�This point is called the equivalence point because this
is where the amount of base in the solution is reacted completely with the amount
of acid in solution. The analyte is the solution being analyzed and the titrant
is the solution contained in the buret. This is a useful experiment in acid/base
chemistry because you can determine pH of an unknown acid or base solution, how
strong an unknown acid or base is or even how concentrated a solution is.
Acid/base chemistry is all around us. Many biological
processes involve acid/base chemistry, for example, blood pH. Your body must carefully
maintain this or serious medical conditions can result. Also, pharmaceutical companies
have made money off of acid/base chemistry.�When a person has heartburn, they
can take an antacid to cure it. This antacid is just a base that neutralizes the
acid in your stomach. A swimming pool is also a good non-biological example of
acid/base chemistry.� When the water is too basic, chlorine is added to it and
when the water is too acidic, potash is added to neutralize. The list goes on
with examples of acid/base chemistry, but with the few examples I have provided,
I hope that that point has gotten across. How many examples can YOU think of?