LabBench Activity

pipette Doing the Titration

To determine how much hydrogen peroxide (substrate) has been broken down by catalase at varying times, you measure the amount of peroxide remaining in each flask.

You slowly add KMnO4, which is purple, to the flask. The peroxide in the flask causes the KMnO4 to lose color when the solution is mixed thoroughly. When all the peroxide has reacted with KMnO4, any additional KMnO4 will remain light brown or pinkish even after you swirl the mixture. This is the endpoint. Record the amount of KMnO4 you have used. (The more KMnO4 you use, the more peroxide is in the flask.)

pipette Lab Hints

  1. Be sure to titrate only 5 ml of the sample at a time. This way, if you exceed the endpoint or have an error in titration, you will have sufficient sample to repeat the titration.
  2. Since you will be comparing amounts of H2O2 remaining in the sample after different reaction times, be sure all your samples are the same size (5 ml).
  3. Place the solution to be titrated over a piece of white background paper so you can see the color changes easily.
  4. Swirl (do not shake) the flask after every few drops to mix well.
  5. For each assay, be sure to stop the titration at the same color.