Titration is the quantitative measurement of an analyte in solution by completely reacting it with a reagent.
The point at which all of the analyte is consumed is called the endpoint and is determined by some type of indicator that is also present in the solution. For acid-base titrations, indicators are available that change color when the pH changes. When all of the analyte is neutralized, further addition of the titrant causes the pH of the solution to change causing the color of the indicator to change.
The analyte concentration is calculated from the reaction stoichiometry and the amount of reagent that was required to react with all of the analyte.
Quicktime movie of a phenolphthalein endpoint in a titration of a weak acid.
Manual titration is done with a buret, which is a long graduated tube to hold the titrant. The amount of titrant used in the titration is found by reading the volume of titrant in the buret before beginning the titration and when the endpoint is reached, and taking the difference. The most important factor for making accurate titrations is to read the buret volumes reproducibly. The figure shows how to do so by using the bottom of the meniscus to read the reagent volume in the buret.
For repetitive titrations, autotitrators with microprocessors are available that deliver the titrant, stop at the endpoint, and calculate the concentration of the analyte. The endpoint is usually detected by some type of electrochemical measurement. Some examples of titrations for which autotitrators are available include:
/chem-ed/titrate/titratn.htm, updated 11/1/96
Copyright © 1996 by Brian M. Tissue, all rights reserved.
Science Hypermedia Home Page