pHkäyriä

pHkäyriä, commonly known as titration curves, are graphical representations that illustrate the change in pH of a solution as a titrant is added. These curves are fundamental in analytical chemistry, particularly for understanding acid-base titrations and their associated properties. The x-axis of a pHkäyrä typically represents the volume of titrant added, while the y-axis depicts the corresponding pH of the solution.

The shape of a pHkäyrä provides valuable information about the strength of the acid and base involved in the titration. For a strong acid titrated with a strong base, the curve is characterized by a steep rise in pH around the equivalence point. The equivalence point is the point at which the moles of acid are stoichiometrically equal to the moles of base. In contrast, titrating a weak acid with a strong base results in a more gradual pH change before the equivalence point, which occurs at a pH greater than 7. The buffering region, where the pH changes slowly upon addition of titrant, is also evident in the titration curves of weak acids and bases.

The midpoint of the buffering region for a weak acid-strong base titration corresponds to the pKa of the acid. This information is crucial for identifying unknown acids or bases and for evaluating the effectiveness of buffer solutions. pHkäyriä are also used in complexometric titrations, precipitation titrations, and redox titrations, though the shape and interpretation of the curves vary depending on the specific type of titration. The data for constructing these curves is obtained by periodically measuring the pH of the solution as the titrant is added using a pH meter.