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This laboratory exercise is presented as an alternative to the traditional AP catalysis lab. The technique is easier for the students to use and yields better results. We use fly vials stoppered with one-hole rubber stoppers (#7) as reaction chambers.
Peroxide is added to the vial and then the students add the yeast mixture (the catalse source) and the whole apparatus is quickly placed in a pan of water. The bubbles generated are collected into the water-filled graduated cylinder and students measure volume of O2 generated by the volume of displaced water.
This system also allows for easy variations in the experiment. To use different percentages of catalase, we reduce the amount of yeast solution added to the peroxide in the vial.
Please see accompanying photos & illustrations to help visualize this system.
The vial is a fruit fly vial, but you can use any container that you can stopper, even larger test tubes. I use #7 rubber stoppers on the vials. You just need a one-hole stopper (to fit whatever vial you use) with a short piece of glass tubing sticking out of the hole. Then attach a length of flexible plastic tubing to that and this will serve as the conduit for the escaping gas bubbles. I got my flexible plastic tubing at the pet store. I use 100mL graduated cylinders to collect the O2.
To make the catalase solution, use 1 package (7g) yeast in 200-250mL warm water (do NOT add sugar so that bubbling is kept at a minimum before use). Since the procedure requires 100%, then 75%, 50%, 25% of enzyme, I make it easy by starting with 1.0ml of yeast catalase. Then we go from 1.0 to 0.75 to 0.5 to 0.25ml. We use 20ml of peroxide as our starting amount of substrate.
After an initial practice, the students had the whole system ready. Then they put the peroxide in the vial first and then added the catalase (yeast solution) to the vial with a pipette. They can plug the vial and slip the tubing into the inverted graduated cylinder well before any bubbles escape. All the other variables are run off of this protocol.
This is so smooth and easy!
Thank you to Dot Gillespie of Nashua High School for introducing this idea to me!