After rearranging the expression defining K, and putting , one obtains
This is the Henderson–Hasselbalch equation, from which the following conclusions can be drawn.
* At half-neutralization the ratio ; since , the pH at half-neutralization is numerically equal to pK. Conversely, when , the concentration of HA is equal to the concentration of A.
* The buffer region extends over the approximate range pK ± 2. Buffering is weak outside the range pK ± 1. At pH ≤ pK − 2 the substance is said to be fully protonated and at pH ≥ pK + 2 it is fully dissociated (deprotonated).
* If the pH is known, the ratio may be calculated. This ratio is independent of the analytical concentration of the acid.
In water, measurable pK values range from about −2 for a strong acid to about 12 for a very weak acid (or strong base).
A buffer solution of a desired pH can be prepared as a mixture of a weak acid and its conjugate base. In practice, the mixture can be created by dissolving the acid in water, and adding the requisite amount of strong acid or base. When the pK and analytical concentration of the acid are known, the extent of dissociation and pH of a solution of a monoprotic acid can be easily calculated using an ICE table.