An investigation to measure the rate of reaction of hydrogen peroxide decomposition by catalase in yeast

The equation is: 

2H2O2 (aq) ⇒ 2H2O(l)+O2 (g)

I predict an increase in rate with higher substrate concentration.  For low concentrations I think that the rate of the reaction will be directly proportional to the concentration of hydrogen peroxide in the solution.  Therefore if there is double the amount of substrate molecules in a solution, double the amount of reactions will take place at once and the rate will be doubled, as long as there are enough catalase enzymes to cope. When there are not enough catalase enzymes to cope, the reaction will tail off, as described in the graph below:

Safety: during this experiment, gloves and goggles must be worn has hydrogen peroxide is corrosive and irritant. Any spillages must be wiped up as soon as possible to avoid accidents and mishaps that could be caused by leaving them.

Variables and controls:

        

If any of the factors are not accurate, I plan to perform up to three repeats in order to produce a reliable graph and measurements.

Apparatus:

• Stand
• Clamp
• Boss
• Gas measuring cylinder, volume 100ml.
• Connecting tubes, to join the flask with the reaction to the gas-measuring cylinder
• Flask – 100ml volume
• Bungs
• Syringes, volume 5ml
• Stop clock, digital
• Boiling tubes, 15
• Pipettes
• Lab coat
• Goggles
• Gloves
• Excess amounts of 5% concentration yeast
• Excess amounts of hydrogen peroxide
• 2 beakers for mixing concentrations – 100ml.

Method

1)        Prepare the boiling tubes, each with 5cm3 of hydrogen peroxide. Prepare only as many as are needed for that day, which will be 5, as well as at least another five spare tubes for repeats. Prepare solutions of 20%, 16%, 12%, 8% and 4%. Do this using water to dilute the solutions, i.e. 16cm2 of hydrogen peroxide and 4cm3 of water is 16%. This should give a decent range and adequate repeats to come to a conclusion.  I decided that boiling tubes are the easiest way to keep the solutions until in use because they can easily be labelled and kept in a rack.  Although slowly, hydrogen peroxide still decays in the absence of a catalyst (even in a fridge).  This could affect the results. My control will be some yeast just left without any hydrogen peroxide.

2)        Set the apparatus up in the way shown above.

3)        Put the 5cm3 of 5% yeast into the flask, ensuring that it has been stirred first, using the syringe, and injecting through the special nozzle. Then zero the timers, and ensure that the gas cylinder is also at it’s zero setting.

4)        Inject the hydrogen peroxide, starting with 20%, and working downward throughout. Ensure that the syringe stays in place, in order to prevent gas release. Make sure that you start the stop clock as you inject the hydrogen peroxide.

5)        Gently stir the flask, and ensure that stirring is constant. When the reaction has reached the stage where it has produced 30cm3 of gas, stop the stop clock, and then disconnect and wash out the tubing, flask and syringe, and anything else that could have come in contact with yeast or hydrogen peroxide.

6)        Enter the results into the table, and if they prove to be inaccurate, repeat. Try and make sure that the repeats are done on the same day, as the conditions are likely to be similar, for instance position in the lab, draught e.t.c. Try and keep away from windows and doors in the first place, but if you have to be there, stay there for the duration.