pH Scale

Instead of writing concentration of $\mathrm{H_3O^{+}}$ ions in mol dm$^{-3}$, sometimes it is convenient to express it on the logarithmic scale. This is known as pH scale.

Sorensen in 1909 defined the pH of a solution as the negative logarithm to the base 10, of the concentration of $\mathrm{H^{+}}$ ions in solution in mol dm$^{-3}$. Expressed mathematically as

Similarly pOH of a solution can be defined as the negative logarithm to the base 10, of the molar concentration of $\mathrm{OH^{-}}$ ions in solution. Thus,

$pOH = -\log_{10}[\mathrm{OH^{-}}] \qquad \text{...(3.16)}$ …