hydrogen peroxide + potassium permaganete with catalyst (maganese dioxide) what will be product
Answers
Description
Several measuring cylinders are set up each containing a little washing up liquid and a small amount
of a catalyst for the decomposition of hydrogen peroxide. Hydrogen peroxide is poured into the
cylinders and a foam rises up the cylinders at a rate that depends on the effectiveness of the catalyst.
Apparatus
- Several 250 cm3 measuring cylinders – one for each catalyst to be used.
- A large tray to catch any foam that spills over the top of the cylinders.
- Stopwatch or clock with second hand.
Chemicals
The quantities given are for one demonstration.
- 75 cm3 of 100 volume hydrogen peroxide solution.
- About 0.5 g of powdered manganese(IV) oxide (manganese dioxide, MnO2).
- About 0.5 g of lead(IV) oxide (lead dioxide, PbO2).
- About 0.5 g of iron(III) oxide (red iron oxide, Fe2O3).
- A small piece (about 1 cm3) of potato.
- A small piece (about 1 cm3) of liver.
Safety
Wear goggles (to BS EN166 3).
Used liver should be wrapped up in paper and placed in the dustbin.
Hydrogen peroxide solution, 100 vol H2O2 (aq) is Corrosive. Wear splash-proof goggles.
Avoid contact of the catalysts with aluminium and other metal powders, explosive reactions can occur.
Manganese(IV) oxide, MnO2 (s) is Harmful if swallowed or inhaled,
© Royal Society of Chemistry, registered charity number 207890.
Lead dioxide, PbO2 (s) is a Reproductive toxin, Harmful if swallowed or inhaled, a Specific
Target Organ Toxin and hazardous to the aquatic environment..
Method
Before the demonstration
Line up five 250 cm3 measuring cylinders in a tray. Add 75 cm3 of water to the 75 cm3 of 100 volume
hydrogen peroxide solution to make 150 cm3 of 50 volume solution.
The demonstration
Place about 1 cm3 of washing up liquid into each of the measuring cylinders. To each one add the
amount of catalyst specified above. Then add 25 cm3 of 50 volume hydrogen peroxide solution to
each cylinder. The addition of the catalyst to each cylinder should be done as nearly simultaneously
as possible – using two assistants will help. Start timing. Foam will rise up the cylinders. The lead
dioxide will probably be fastest, followed by manganese dioxide and liver. Potato will be much slower
and the iron oxide will barely produce any foam. This order could be affected by the surface areas of
the powders. Time how long each foam takes to rise to the top (or other marked point) of the cylinder.
The foam from the first three cylinders will probably overflow considerably.
Place a glowing spill in the foam; it will re-light confirming that the gas produced is oxygen.
Teaching tips
Some students may believe that the catalysts – especially the oxides – are reactants because
hydrogen peroxide is not noticeably decomposing at room temperature. The teacher could point out
the venting cap on the peroxide bottle as an indication of continuous slow decomposition. Alternatively
s/he could heat a little hydrogen peroxide in a conical flask with a bung and delivery tube, collect the
gas over water in a test-tube and test it with a glowing spill to confirm that it is oxygen. This shows
that no other reactant is needed to decompose hydrogen peroxide.
NB: Simply heating 50 volume hydrogen peroxide in a test-tube will not suceed in demonstrating that
oxygen is produced. The steam produced will tend to put out a glowing spill. Collecting the gas over
water has the effect of condensing the steam. It is also possible to ‘cheat’ by dusting a beaker with a
tiny, almost imperceptible, amount of manganese dioxide prior to the demonstration and pouring
hydrogen peroxide into it. Bubbles of oxygen will be formed in the beaker.
Theory
The reaction is :
2H2O2(aq) → 2H2O(l) + O2(g)
This is catalysed by a variety of transition metal compounds and also by peroxidase enzymes found in
many living things.
Extensions
Repeat the experiment but heat the liver and the potato pieces for about five minutes in boiling water
before use. There will be almost no catalytic effect, confirming that the catalyst in these cases is an
enzyme that is denatured by heat.
© Royal Society of Chemistry, registered charity number 207890.
Investigate the effect of using lumpy or powdered manganese dioxide. The powdered oxide will be
more effective because of its greater surface area.
Try using other metal oxides or iron filings as catalysts.
Animal blood may be used instead of liver if local regulations allow this.
One teacher suggested measuring the height of the foam over suitable time intervals and plotting a
graph.
Further details
The experiment can be done with 20 volume hydrogen peroxide, but is less spectacular. It is,
however, easier to time.
It has been suggested that manganese dioxide is not in fact the catalyst for this reaction, but that the
catalysts are traces of other oxides found on the surface of manganese dioxide.
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