Practical investigations
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Investigating the catalytic decomposition of hydrogen peroxide
Hydrogen peroxide tends to decompose into water and oxygen but normally the reaction is slow in the absence of a catalyst.
LITERATURE REVIEW
Start by finding out about the decomposition of hydrogen peroxide from text books and the internet. Keep a note of all sources of reference (including URLs) so that you can itemise them in your report.
Which compounds are reported to act as catalysts for the decomposition of this compound?
Look in the catalogues of chemical suppliers to see what a typical solution of hydrogen peroxide consists of and how concentrated it is.
Ask your teacher, or the technician, how old your supply of hydrogen peroxide is so that you can assess whether it is likely to be as concentrated as shown on the bottle.
PRELIMINARY TESTS
Explore on a small scale the effect of adding a range of possible catalyst to small samples of hydrogen peroxide solution. Try different concentrations. In this way you will get a feeling for the rate of change and the quantities involved.
Some people have tried to investigate the effect of the surface area of the catalyst on the rate of reaction. Is this realistic? What catalysts are you going to use and is there some realistic way of varying and measuring the surface area?
Write the equation for the decomposition and estimate the volume of oxygen expected from a likely quantity of the hydrogen peroxide solution you are using. (Keep a note of any such calculations and include them in the planning section of your report.)
PRACTICAL METHODS
You can follow the procedure for the decomposition of hydrogen peroxide in a similar manner to experiment 11.2a in the Nuffield Students’ Book, as described on pages 245 and 246. In both cases a gas is evolved. In experiment 11.2a it’s carbon dioxide and in your case it’s oxygen. You can either follow the reaction by measuring the volumes of oxygen given off at set time intervals, or you can follow the loss in mass at various times (both methods are described in the book).
These methods will work well in your case. You can subtract each volume (or mass) from the final reading (as explained on page 246) and then, by plotting (Vfinal – Vt) or (massfinal – masst) against time, you can draw a curve of best fit, and then measure half lives. If these remain approximately constant the reaction is first order, but if the half live doubles as the concentration halves, then the reaction is second order. All this is explained on page 247.
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Help me!
Does anyone have activation energies for MnO2, PbO2 or PbO?
07 April 2006
Anonymous
08 February 2004
updated: 12 January 2007
