Methods 

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.

Apparatus:                                         Diagram of apparatus (draw):

• ½ litre container
• Boiling tubes
• Five litre ice-cream tub
• Retort stand
• Three clamps
• Buckner flask (with tube and bung)
• Stop clock
• Pipette
• Burette

Instructions:

• Prepare boiling tubes, each with 25 ml of hydrogen peroxide in them (only prepare as many as will be used on that day).  Prepare solutions of 20%, 17.5 %, 15%, 12.5%, 10%, 7.5%, 5%, 2.5% and 0%.  There should be three test tubes of each concentration for the repeats.

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 labeled and kept in a rack.  Although only slowly, hydrogen peroxide still decays in the absence of a catalyst (even in a fridge).  This could affect the results.
 

• Set the apparatus up in the way shown above, making sure that no (or as little as possible) air leaks into the burette when it is inverted with the open end underwater.

Clamping the apparatus in place enables me to concentrate on running the experiment and not have to hold anything.
 

• The tube must be fixed under the burette, with a funnel directing the air bubbles into the burette.

It is also possible to do it without a funnel.  The funnel is to prevent the pressure of the air being pushed into the burette from causing the pipe to pop off or oxygen to be leaked from the system (squeezed out).  Any pressure build up could also lead to inaccuracies.
 

• The burette must only have the part of it with no scale underwater (so that a maximum amount of gas can be collected to reduce the percentage error).

The gas could have also been collected in a gas syringe or over water in a measuring cylinder, but the latter is not as accurate as a burette because of the smaller graduations and larger distance between the outside and the centre of the meniscus and the former is not as reliable as a burette because of the friction in the system causing pressure and possible leaks to affect the results.
 

• The tube that carries oxygen to the burette must be put into the water in such a way that no air is trapped underwater that could rise into the burette to spoil the set up or the results.

This is worth doing because if a bubble goes into the burette before the experiment starts it is very annoying to have to get the waterline back to 50 ml.
 

• When this is all ready, prepare five 1-cm-long cylinders of potato, using borer size 4.  Make sure that there are no skins on the cylinders.

There is no point in having fast reactions if the percentage inaccuracies in timing, caused by the short times and the percentage inaccuracies in surface area caused by cutting the potatoes into very small pieces by hand (a variation of about 0.5 mm either side), are so large that the results are inconsistent.  However, too slow a rate, however low the percentage inaccuracies may be, is impractical, as I do not have all the year to do this in.  I therefore decided on cylinders of 1 cm length made with a fairly thin borer (size 4) so that the circumference was constant (and small enough to give the cylinders a large enough surface area) and the inaccuracy was reduced (1 mm in 10=10%).  Trying this out, I realised that the inaccuracy was still much greater than I would have liked it to be. I therefore weighed them too, to insure that all the pieces of potato had the same mass. This gives them the same volumes (presuming that the variations in density, caused by a gradual water loss by osmosis and the retention of the shape of the cells by the cell wall, are negligible) and therefore, if the pieces are flat ended cylinders of equal radius, the same surface area.  The scales/balance weighed to an accuracy of one hundredth of a gram. My pieces were 0.5g.  The inaccuracy was therefore 0.01/0.5 =2%, 1/5th of what it would be without the scales.  Skin on the cylinders must be avoided because this would have a large effect on the surface area.
 

• Then pour the first 20 ml of hydrogen peroxide into the conical flask and start the stop clock as the bung goes into the flask.

I decided to use 20 ml because I thought that this seemed about the right amount and 20 would divide easily to dilute the hydrogen peroxide.  A stop clock is most suitable because it is accurate and can easily be stopped and started without looking at it.e
 

• After five minutes enter the amount of gas collected in the burette on the table, making sure that this point is at eye level to eliminate parallax error.

I decided to collect as much gas as possible if I had time, because this would reduce the percentage errors.  If the point on the burette is not at eye level, the thickness of the burette and distance to the centre of the meniscus could throw the measurements out. 
 

• Stop the stop clock as soon as the burette is full of gas (again, make sure that this point is at eye level to eliminate parallax error).  The stop clock should be stopped the moment the bubble reaches the surface.

The moment that the bubble reaches the surface of the column of water in the Burette is better than their moment at which it comes into the Burette because one the can see it rising in that the Burette and get ready to stop the stop clock.
 

• Enter this time and the temperature of the solution in the Buckner flask, together with the corresponding concentration and in the correct column for which repetition of the experiment it is on the table. 

I decided to take the temperature of the reactants, because this is the temperature at which the reaction occurs, and the temperature affects the rate of the reaction.  I could then use the Q10 formula to “temperature balance” the results. 
 

• Repeat the experiment three times for each concentration of hydrogen peroxide.

As I have said earlier, the more repetitions the better, and if they are not done on the same day as each other, all the better to prevent factors like which potatoes I was using and draught in the lab from affecting my average results.

For one of the reactions, take readings of the amount of gas in the burette every 30 seconds.  This is to show the activity decrease curve throughout the individual reactions.