| − | A '''conjugate base''' is the negatively charged [[ion]] which results from an [[acid]] donating a [[proton]] (H<sup>+</sup>). This ion acts as a [[base]], with a strength inverse to the strength of the original acid. An example conjugate base is a [[nitrate]] ion (NO<sub>3</sub><sup>-</sup>), which is formed when [[nitric acid]] (HNO<sub>3</sub>) gives up its proton.
| + | Consider the pair of molecules HX and X<sup>−</sup>. X<sup>−</sup> can react to form HX, and vice versa, through an [[acid-base reaction]]. Thus, X<sup>−</sup> is the conjugate base of HX (and HX is the conjugate acid of X<sup>−</sup>.) |