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Rate of decomposition of H2O2

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Downloads to date: N/A | Words: 1296 | Submitted: 10-Jan-2012
Spelling accuracy: 98.0% | Number of pages: 8 | Filetype: Word .doc

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Rate of decomposition of hydrogen peroxide, catalysed by MnO2 at RTP

This is a safe, tested and quick experiment that can be done in a single period.

It enables pupils to use two methods
Measuring the mass of oxygen lost – using a 3dp balance – and plotting Mf-Mt v time

Measuring the volume of oxygen formed – 100cm3 syringe, and plotting Vf-Vt v time

It enables students to do an Excel graph with a good R2 value (0.98- 0.99), obtain an exponential decay curve to show that the that the decomposition is first order w.r.t peroxide

Note there are only 2 suitable 3 dp balances, and so it might be a good plan for 2 pairs to use the balances and the remainder to use gas syringes.

Safety

Hydrogen peroxide bleaches skin and is dangerous to eyes. Students should be told:
Wear goggles
Wash hands immediately if any spillages occurs
Keep the desks clean and dry
Most importantly: Avoid rubbing their eyes.

Typical results, for a) the mass loss method.


























Typical student results for b) the Volume of oxygen produced experiment.


Technicians:

Please issue:

200cm3 of 1 Volume Hydrogen peroxide per pair,
Two 3 d.p. Balances (Precisa)
Two 2 d.p. Balances to weigh the catalyst
MnO2 (1 jar); pestle & mortar;
2 clocks.
1 x 100cm3 syringe per pair
One 250cm3 conical flask with bung and connector to the syringe per pair.
2 jars of anti-bumping granules
2 weighing bottles per pair using syringes.








Rate of decomposition of hydrogen peroxide, catalysed by MnO2 at RTP

Aim: To find the order of reaction with respect to the [Hydrogen peroxide] by two methods.

Hydrogen peroxide decomposes to give oxygen by the following equation. The reaction is slow in the absence of UV light and a transition metal catalyst.

2 H2O2 (aq) 2 H2O(aq) + O2(g)

Method a) Using a 3 decimal place balance

If the reaction is done in an open conical flask oxygen escapes and there is a mass loss.

Tare a 250cm3 conical flask on a 3d.p. balance
Add about 0.10g of MnO2 solid (previously ground using a pestle & mortar)
Tare the flask again.
Separately add 100 cm3 of 1 Volume hydrogen peroxide solution into another 250cm3 conical flask

Put this flask onto the balance along with the other flask. Tare the balance with the 2 flasks







Pour the hydrogen peroxide solution onto the catalyst. Start the clock when half the solution has been added. Put the empty conical flask back on the balance (so that the tare weight of 0 is maintained)

Quickly pick up the conical flask with the solution it and swirl it 3 times to mix the ...

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