DECOMPOSITON OF HYDROGEN PEROXIDE WITH HEAVY METAL CATALYSTS

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DECOMPOSITON OF HYDROGEN PEROXIDE WITH HEAVY METAL CATALYSTS

Aim: Various metal oxides will be added to the hydrogen peroxide and the production of oxygen of the reaction mixture will determine catalysis. The volume of oxygen evolved will be observed and recorded to measure the reaction rate and the reaction rates of the different metal oxides will be compared.

Scientific Background:  Catalysis is the process by which the activation energy is lowered to allow the reaction to occur at less extreme conditions, during the process the catalyst does not under go any overall change. The catalyst reduces the activation energy by using a chemical route with activation energy less then the route, which would otherwise be taken in the absence of the catalyst. During catalysis the reacting substance usually undergoes a change or changes in oxidation state, therefore the catalyst must also be able to change its oxidation state. The s & p block metals possess or exhibit only one oxidation state. The reason being that their oxidation state depends on the removal of electrons from their outermost shell. The further removal of electrons will result in the penetration of stable inner shells that are filled with electrons. This would require an excessive amount of energy. As a result of this, the catalysts are not able to enter their different oxidation states and this therefore does not allow them to successfully act like a catalyst. Transition metals can form ions, which have D orbitals, which are partially filled with electrons. D orbitals are the outer most shells and they can hold up to 10 electrons and they also have similar energy levels, which allows them to overlap within each other. It is this process which allows the transition metals to have various oxidation states. The orbital possess the same energy, which enables transition metal ions to enter their different oxidation states. This therefore allows them to act as catalysts. As there are more spaces for electrons to be lost and gained the reaction can take place faster and better.

The general equation for the experiment is:

CATALYST

2H2O2                                  O2+2H20

From the equation it can be seen that Oxygen is produced in the reaction and this is what is being collected and measured in the gas syringe.

Prediction: The transition metal oxides MnO2 (Manganese oxide), ZnO (Zinc Oxide) and CuO (Copper Oxide) will be compared with SiO2 (Silicon Oxide), A12O3 (Aluminium Oxide) and PbO (Lead Oxide) which are transitional metal oxides to see their action on hydrogen peroxide and therefore see if only the transition metal oxide allow catalysis or that all metal oxides allow catalysis for this reaction.

Apparatus: 

In the experiment, 20cm3 of water and 20cm3 of hydrogen peroxide will be used.

The above apparatus is easy to use and will give quick results; a stop clock will be used to see how much gas is collected in a given time. The conical flask is used to keep the solution in and the rubber bung is placed on top firmly to prevent any loss of gas, which would obviously affect results.

The following oxides will be chosen for the experiment:  SiO2, A12O3, PbO, MnO2, ZnO and CuO. 1 gram of each oxide shall be used

SiO2, A12O3 and PbO are not transition metal oxide, whereas MnO2, ZnO and CuO are transition metal oxide.  They will be used to compare the catalytic action if any of transition and non-transition metal oxide on hydrogen peroxide.

1 gram of each oxide allows a sensible amount of oxide to be used without causing a dangerously vigorous reaction to occur.                

Variables:

The following variables will be controlled throughout the experiment:

Temperature can affect the reaction rate of H2O2 decomposition. Two molecules can only react if they have enough energy, by heating a mixture the energy levels will be raised of the molecules involved in the reaction. Therefore, by increasing the temperature the molecules will move faster and collide with each other more quickly. This will increase the rate of reaction and so the temperature will be kept constant throughout the experiment by carrying it out under room temperature.

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Concentration and volumes of the hydrogen peroxide must be kept constant because if there are more molecules of a particular substance in a certain volume then there is more of a chance of the molecules colliding with each other. The frequency of collisions is increased which increases the rate of reaction. Thus the hydrogen peroxide must be kept constant for each run of the experiment with a metal oxide. The amount of oxide must also be kept constant for the same reasons.

Particulate size could affect the rate of reaction as if the particle sizes are larger then the rate ...

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