Calculating pH

The pH scale is estimated from the concentration of hydrogen ions.

pH = - log [H⁺]

For strong acids and bases, [H⁺] can be directly derived from the concentration of the acid or base.

For weak acids and bases, the [H⁺] needs to be calculated from the K_a.

K_a = ( [H⁺] [A^¯] ) / [HA]

For buffers, the pH can be calculated using the Henderson-Hasselbalch equation.