D20.1 Titration

At this point, you have already seen several titration experiments in lab. In a titration, one solution is added to a second solution in a way that allows the quantity of each solution to be measured accurately. Typically, one solution is added from a buret, a calibrated glass tube with a stopcock at the bottom. The buret allows additions of very small increments of solution and determination of the total volume added. The solution added from the buret is the titrant. Titrant is added to a carefully measured volume of a second solution in a flask or beaker.

A chemical reaction occurs between solutes in the two solutions, and when just enough titrant has been added for complete reaction with the second solution, the equivalence point of the titration has been reached. From the balanced chemical equation for the titration reaction, the volume of each solution at the equivalence point, and the concentration of one of the two solutions, the concentration of the other solution can be determined.

The equivalence point of a titration may be detected visually if there is a color change that accompanies the completion of the reaction. Typically, a special dye called an indicator is added to the solution being titrated to provide a color change at or very near the equivalence point. Equivalence points may also be detected by measuring a solution property that changes in a predictable way during the course of the titration, such as pH.

Regardless of the approach taken to detect a titration’s equivalence point, the measured total volume of titrant added is called the end point. A properly designed titration typically ensures that the difference between the equivalence point and the end point is negligible.

Although any type of chemical reaction may serve as the basis for a titration analysis, precipitation, acid-base, and oxidation-reduction titrations are most common.