To achieve our goal of understanding how acids and bases work, we
must first define what acids and bases are. There are three distinct
conceptions of
acids and bases that will be considered in this SparkNote--the Arrhenius
model, the Bronsted-Lowry model, and the Lewis model. Each of these
models describe an acid-base reaction as a process by
which a transfer occurs between two partner reagents, the acid and the base.
For our purposes, the most useful model is
the Bronsted-Lowry model, because we will be considering reactions involving
proton transfers. Bronsted and Lowry described acids as proton donors and bases
as proton acceptors. Calculations and measurements of pH are relevant to
the Bronsted-Lowry conception of acid-base reactions. We will discuss each of
the three models of acid-base reactions using representative equations.
To speak of acid or base strength, we need scales for acidity and
basicity. pH and pOH scales are quantitative representations of these
values for acidic and basic solutions. Next, we will define the acid
dissociation constant,
Ka, and the base dissociation constant,
Kb, to quantify the strengths of particular acids and bases.
These terms allow us to process acid and base strength mathematically and
package them into values that we can gage conceptually. Using reference values,
we can then see that a solution with pH 6 is weakly acidic, since it is slightly
lower in pH than water at pH 7.
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