The setup: burette, beaker, and detecting the equivalence point

The titration equipment

A typical titration uses a simple but precise setup:

• a graduated burette, fixed vertically on a stand, containing the titrant (the solution whose concentration is known);
• a beaker (or an Erlenmeyer flask), placed under the burette, containing a precise volume of the titrated solution, often measured with a volumetric pipette;
• a magnetic stirrer, to continuously homogenize the mixture while the titrant is being added.

burette (titrant solution)
      |
      v  (the liquid flows drop by drop)
beaker (titrated solution + magnetic stirrer)

How to spot the equivalence point

The challenge is knowing precisely when the equivalence point has been reached, since the reaction is invisible to the naked eye. Two main methods exist:

• an acid-base color indicator (such as phenolphthalein or bromothymol blue), a chemical species that changes color depending on the pH: its color shifts abruptly near the equivalence point;
• a pH meter, a probe that measures pH continuously: you then plot the pH curve as a function of the volume added, and the equivalence point corresponds to the point where the curve shows the sharpest pH jump (located using the tangent method).

Why the pH meter is more precise

A color indicator gives a visual result, dependent on the experimenter's eye and the color-change range specific to the chosen indicator. A pH meter gives an exact numerical value, which makes it possible to locate the equivalence point with much greater precision, especially for reactions where the pH jump is not very pronounced.

Common mistake

Never add the titrant too quickly near the equivalence point: the color change (or the pH jump) is very abrupt, and a single excess drop can make you significantly overshoot the equivalence point, throwing off the entire calculation that follows.