Properties of Acids and Bases

Acids and bases are compounds with unique properties and behaviors. In general, acids have a tart
or sour taste, are usually liquids and gases, conduct electricity well, and react with metals. Bases, in
contrast, are often solids, feel slippery, and tend to attack oils and greases.

The behavior of acids and bases in solution is governed by equilibrium considerations. Some
concepts you already may be familiar with will appear with new names in this context.

HYDROGEN ION EQUILIBRIA (pH AND pOH)

Hydrogen ion or proton concentration, [H+], like concentrations of other particles, can of course be
measured in the familiar units like molarity. However, it is more generally measured as pH, where:

where [H+] is its molarity and the logarithm is of base 10. (Log x) is the power to which 10 would be
raised to obtain the number x, i.e.:

log x   =   p   10 p    =   x

Likewise, hydroxide ion concentration, [OH−], can be measured as pOH where:

It turns out, however, that pH and pOH are not totally independent of each other: Knowing one
would allow us to calculate the other. This is because in any aqueous solution, the H 2 O solvent
dissociates slightly: