ekvivalenssipiste

Ekvivalenssipiste is a term used in analytical chemistry, particularly in titration analysis, to describe the point at which the stoichiometric amount of a titrant has reacted with an analyte. At this juncture the number of moles of reacting species are equal, so the reaction has theoretically reached completion. In acid–base titrations this point usually manifests as a sharp change in pH, and for strong acid–strong base titrations it is marked by the pH equal to seven. For weak acid–strong base or weak base–strong acid systems the pH at the equ­ivalence differs from neutral and is determined by the acidity or basicity of the weak species.

Practically, the equ­ivalence is observed by instruments such as a pH meter or by using indicators that change color near the anticipated value. When a titrant is added incrementally, a graph of pH versus added volume will show a sig­nificant inflection point at the equ­ivalence; the volume at that point is used to calculate the concentration of the analyte through a simple stoichiometric equation. The concept is central not only to routine quantitative analysis but also to determining the dissociation constants of acids and bases and to establishing buffering capacity in solutions.