ACIDS, BASES, SALTS, AND pH
Fundamentals of Chemistry
When an acid reacts with a base, two products are formed; water and a salt. A salt is an ionic
compound composed of positive ions and negative ions. The ionic bond is what keeps salts in
their molecular form. Some compounds look like salts, but are actually covalent compounds
(have a covalent bond).
This type of acid-base reaction is called neutralization.
Certain soluble salts (principally sodium, potassium, magnesium, and calcium) that have the
property of combining with acids to form neutral salts are called alkalies. Two of the common
salts are sodium chloride (table salt) and calcium chloride (salt put on the road in winter).
Unlike acids and bases, salts vary greatly in all their properties except their ionic characteristics.
Salts may taste salty, sour, bitter, astringent, sweet, or tasteless. Solutions of salts may be
acidic, basic, or neutral to acid-base indicators. Fused salts and aqueous solutions of salts
conduct an electric current. The reactions of salts are numerous and varied.
Many compounds dissolve in water and alter the hydrogen ion concentration. Compounds that
produce hydrogen ions directly when dissolved in water are called acids, and those that produce
hydroxyl ions directly when dissolved in water are called bases. To treat these aspects of
chemistry more precisely, a quantitative system of expressing acidity or basicity (alkalinity) is
needed. This need could be met by using the value of [H ], where [H ] is expressed in
moles/liter, as a measure of acidity. But, in most cases [H ] is in the range of 10 to
10 moles/liter. Because numbers of this magnitude are inconvenient to work with, an
alternate system for expressing the acidity of dilute solutions has been devised. This system is
based on a quantity called pH. ph is defined as the negative logarithm of the hydrogen
concentration, represented as [H ] in moles/liter.
= -log [H ]
[H ] = 10
The negative logarithm is specified because the logarithm of any number less than 1 is negative;
thus multiplication by -1 causes the values of pH to be positive over the range in which we are
interested. (The term pH was first defined by a Danish chemist and is derived from p for the
Danish word potenz (power) and H for hydrogen.)