pH and BUFFERS
Section I. INTRODUCTION
a. The interaction of charged particles in which the total number of protons do
not equal the number of electrons is responsible for many chemical reactions. These
charged particles are called ions. A cation is an ion in which the protons are more
numerous than the electrons (+ charge), and anions are ions in which the electrons
outnumber the protons (- charge). These oppositely charged ions are attracted to each
other and form bonds called ionic bonds. When ionically bound compounds are
dissolved in a solvent, the ions separate. This separation is known as dissociation or
ionization. The only way in which most ions can undergo chemical reaction is to be in
this dissociated state.
b. Three general types of ionic compounds exist: acids, bases, and salts.
Simply and incompletely stated, acids are compounds that contribute hydrogen ions to a
solution, bases are compounds that contribute hydroxide ions to the solution, and salts
yield neither hydrogen nor hydroxide ions to the solution. The concentration of the
hydrogen and hydroxide ions will determine the degree of acidity or alkalinity of a
solution, and thus have an effect on the kinds of reactions and the speed of the
reactions that will occur. It is important, therefore, to know the relative concentrations of
the hydrogen and hydroxide ions in a solution.
c. Before discussing hydrogen and hydroxide ion concentration further, it will be
important to consider in greater detail the definition of an acid and a base. There are
several definitions of the terms acid and base. We will examine two of the definitions
that will aid you in further course work.
An acid is a substance that will produce hydrogen ions (H ) in an aqueous
solution, and a base is a substance that will produce hydroxide ion (OH ) in an aqueous
solution. It is important to note that hydrogen ions do not exist as such in an aqueous
solution. Each hydrogen ion is associated with one molecule of water to produce a
hydronium ion, H3O .
H + H2O <====> H3O