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British Columbia Institute of Technology
Chemistry Department - 3700 Willingdon Avenue
Burnaby, B.C. Canada V5G 3H2
Experiment 7 - Acetic Acid Content of Vinegar
We look for a colour change in the solution in the Erlenmeyer flask. Prior to the start of a titration, a few drops of an indicator is added to the solution in the Erlenmeyer flask. A common indicator that is used in acid-base titration is called phenolphthalein. Phenolphthalein is an acid-base indicator, which is colourless in acid solution and turns pink when the solution becomes slightly basic. When a colour change in the solution in the Erlenmeyer flask is observed, we have reached the end point of the titration. The end point of the titration indicates that we have added slightly more titrant than necessary to neutralize the acid (or base) in the Erlenmeyer flask. This slightly more titrant that is added is necessary to bring about an observable colour change in the solution in the Eerlenmeyer flask. This is a built-in error in using titration as a technique to determine solution concentration. The important thing is to minimize the titration error by being sensitive to observe the colour change and stopping the addition of the titrant once the colour change is observed.