The pH scale

The concept of pH originates from the ion product of water.

(2.5)

Taking logarithms:

(2.6)

Multiplying by – 1:

(2.7)

–log[H ⁺] and –log[OH ^-] are defined as pH and pOH, respectively where “p” denotes the negative logarithm. Equation 2.7 can therefore be written as:

pH + pOH = 14

(2.8)

The above discussed definition of pH does not pose any limits on the values it can take. It is however convenient to define a pH scale ranging from a concentration of 1 M H⁺ to 1 M OH^- . The pH scale thus obtained ranges from 0 – 14. It should be clear by now that pH is a scale for defining the acidity or basicity of aqueous solutions. A solution having a pH<7 is acidic while that having a pH>7 is basic.

pH is an important concept for living organisms. pH defines the ionization state and therefore the function of the biomolecules; most biomolecules function within a narrow pH range.