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.
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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:CATALYST2H2O2 O2+2H20From 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 usedSiO2, 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.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 of reaction will be slower because there is a smaller surface area for the substance to react on. By crushing the catalysts to have the same particle sizes this can be controlled.The key variable is the one, which will be the one, which is varied in the experiment. In this case it will be the metal oxide used in the experiment, which will be varied.Preliminary Experiment:A preliminary experiment was carried out using the same apparatus and the catalysts used were manganese oxide, iron oxide and lead (iv) oxide. The manganese oxide worked well as a catalyst but no results could be collected as the reaction went to quickly. This is most probably due to the amount of oxide being too much. No results were collected for iron oxide, and lead (iv) oxide because they did not produce any gas and therefore did not work as catalysts.
The apparatus seemed appropriate however, a clamp stand was not used to hold the syringe up and so the apparatus can be modified so that the gas syringe is supported by the clamp stand. The other modifications, which need to be made, are the catalysts being used and amount of oxide. The amount of oxide used in the preliminary experiment was 2 grams and so this can be reduced to 1 gram to decrease the rate of the reaction so that a good set of results can be collected.Method:1 – Measure out using a measuring cylinder 20cm3 water and 20cm3 hydrogen peroxide and add to a conical flask.2- Using the balance to weigh out accurately 1 gram of MnO2.3- Using the filter paper used to weigh the oxide add the oxide to the hydrogen peroxide, and immediately stopper the flask with the connecting tube attached to the bung.4- Immediately start the stop clock and see how much gas is collected the gas evolved will push the syringe itself; therefore do not touch the syringe.
Readings should be taken every 10 seconds.5- Record how much gas if any is collected until the syringe stops moving itself.6- Repeat the experiment with MnO2 so three sets of results can be collected to find an average.7- Do 1-6 with the remaining oxides and tabulate the results.Safety: Hydrogen peroxide is a corrosive liquid and should therefore be used sensibly and eye and skin contact should be prevented. Manganese IV Oxide is harmful and again skin contact should be avoided. An overall should be worn when handling hydrogen peroxide. Goggles should be worn when adding the oxide to the peroxide, although they are not needed throughout the rest of the experiment.
Reliability of Results:* When collecting the gas, the attachment of the rubber bung should be very quick to minimise any loss of gas.* The hydrogen peroxide should be measured out accurately. The oxides should also be weighed accurately using an accurate balance.* The oxides should all be in solid powdered form and not in any other form, as this will effect how the catalysts react with the hydrogen peroxide. If the surface area is different on the catalysts then they will react more/less violently.* The apparatus should be cleaned after each run with water to remove any impurities that may affect the next experiment.* The timing of each experiment should be accurate and a digital stop clock should be used.