pH

Potential of hydrogen (pH) is a scale that measures the acidity or alkalinity of a solution. Values for pH range from 0 (strongly acidic) to 14 (strongly alkaline or basic). The pH of a neutral solution, such as pure water, is 7, whereas the pH of an acidic solution is less than 7 and the pH of a basic solution is greater than 7. The pH scale is logarithmic, meaning that each value is 10 fold the next (for example, a pH of 12 is 10 times more basic than a pH value of 11).

pH is defined by

$pH=-log\left[H_{\mathrm {3} }O^{+}\right]=log{\frac {1}{\left[H_{\mathrm {3} }O^{+}\right]}}$

Because of concentration of hydroxide ions times the concentration of hydronium ion is constant, namely

$\left[H_{\mathrm {3} }O^{+}\right]\left[OH^{-}\right]=1.0x10^{-14}$

$\left(pH+pOH\right)=14$

where pOH is defined in a manner similar to pH, as shown below.

$pOH=-log\left[OH^{-}\right]=log{\frac {1}{\left[OH^{-}\right]}}$