Catalysts. The effect of various catalysts on the rate of decomposition of hydrogen peroxide (H 2 O 2 )

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1 Catalysts The effect of various catalysts on the rate of decomposition of hydrogen peroxide (H 2 ) This content is aimed at KS3/4 students and is a two lesson worksheet (including a practical demonstration) to introduce and study catalysts.

2 Learning Objectives: To understand that a catalyst can be used to increase a rate of reaction. To learn that different catalysts work with different efficiencies. To understand that catalysts are neither reactants nor products and remain unchanged after the reaction is complete. To practice designing a fair, accurate and reliable test. To understand that catalysts work by offering an alternative reaction pathway with a lower activation energy. The primary program of study for this worksheet is chemistry although it also includes elements of mathematics, physics and biology. Key Vocabulary: Reactant Product Catalyst Rate of reaction Reaction pathway Activation energy Endothermic / Exothermic reaction Qualitative / Quantitative experiment

3 Lesson 1 Starter activity: Find the correct answer from the 3 options given Question What is present at the start of every chemical reaction? H 2 is better known as Repeating an experiment many times would make the result more Oxygen atoms in the air are mostly found in the form of Answer reactant oxygen catalyst water hydrogen peroxide hydrogenated oxygen reliable safe accurate O C In chemistry, a product is a chemical which can be sold is present at the end of a reaction is not present naturally and has to be artificially produced

4 Practical Resources: 6 x 250ml measuring cylinders 6ml washing up liquid 90ml (6 x 15ml) hydrogen peroxide 15% (50 vol) Catalyst 1: 0.5g manganese(iv) oxide (Mn ) Catalyst 2: 0.5g lead(iv) oxide (Pb ) Catalyst 3: 0.5g copper(ii) oxide (CuO) Catalyst 4: 1cm 3 liver Catalyst 5: 1cm 3 boiled liver Safety: Wear eye protection and gloves when performing the experiment. It is the responsibility of teachers to perform an appropriate risk assessment. Method: Place the 6 250ml measuring cylinders on a tray and add each of the 5 catalysts to 5 of the cylinders. Leave 1 cylinder empty as this will be the control. Add 1 ml of washing up liquid to each measuring cylinder. Simultaneously add 15ml of 15% hydrogen peroxide solution to each measuring cylinder.

5 Introductory questions: In BLOODHOUND SSC one method of propulsion is a rocket engine which uses hydrogen peroxide as a fuel. 1. Write a balanced chemical equation for the decomposition of hydrogen peroxide (H 2 ). 2H 2 + 2H 2 O 2. What effect do you predict the presence of a catalyst will have on the rate of reaction? The rate of reaction will increase 3. What is the independent variable? The type of catalyst used 4. What is the dependant variable? The rate of reaction (or the amount of / H 2 O produced in a specific time) 5. What do you expect to see? Remember; the washing up liquid is not reactant, it is only there to help visualise the reaction. The oxygen produced will form foam/bubbles in the washing up liquid Post-demonstration questions 6. What did you observe? Bubbles of oxygen were produced at differing rates depending on the catalyst present. The reaction catalysed by lead oxide was the fastest; followed by manganese, copper and then liver (which contains a peroxide enzyme). Boiled liver (where the peroxidase enzyme has become denatured) and the reaction with no catalyst produced almost no bubbles. 7. Was the result as you predicted? If not, why not?

6 8. Was the test fair? Consider any factors that may have affected the results but were not well controlled. 9. Suggest any improvements to make the experiment fairer. Answers to questions 7-9 should all involve ways is which the experiment was unfair. Possible answers include mention of: Surface area of catalysts. Amount of each catalyst (extra credit for discussion of moles of each). Time of the start of the reaction, was it simultaneous? Possible contamination of catalysts. Accuracy of the volumes of hydrogen peroxide and/or washing up liquid added to each catalyst. Any other reasonable suggestion of a source of inaccuracy, unreliability or unfairness. Plenary Write a short paragraph summarising the results of the experiment.

7 Lesson 2 Starter Activity In relation to the experiment you did last lesson, which of the following statements are true and which are false. a) Hydrogen peroxide and water reacted to produce oxygen. False b) The chemical equation for the reaction was 2H 2 + Catalyst 2H 2 O + False c) The chemical reaction for the reaction was Catalyst 2H 2 2H 2 O + True d) Washing up liquid was used in the experiment but was not a reactant, it was only there to visualise the gas production. True e) In the reaction without a catalyst the reaction still happened, just at a much slower rate. True f) The independent variable in the experiment was the type of catalyst present. True g) All the catalysts sped up the rate of reaction by the same amount. False h) and H 2 O were the products in each reaction, just different amounts were produced in the specific time. True i) The liver contained a biological catalyst (enzyme) which was almost completely denatured (the functionality was lost) by boiling. True

8 Energy Activation energy 1. Draw your own reaction coordinate diagram for the decomposition of hydrogen peroxide both in the presence and absence of a catalyst. Include the specific reactants and products and be sure to label your axis. Mark on your graph which parts represent the activation energy (Ea) and total energy change (ΔE) for the reaction. H 2 Ea Ea - No catalyst - With a catalyst ΔE + H 2 O Reaction Path

9 Energy distribution 2. On the energy distribution diagram above draw how the graph would change in each of the following situations: a) The reaction is performed at a higher temperature Number of Particles Room temperature Higher temperature Energy b) The reaction is performed in the presence of a catalyst Number of Particles No catalyst With a catalyst Energy

10 3. In this experiment hydrogen peroxide was used at 15% concentration. Another way of expressing this concentration is 50 volume. The 'volume' method of measuring concentration is defined by the volume of oxygen produced when compared to the volume of the reactants (at standard room temperate and pressure) i.e. hydrogen peroxide at 15% decomposes to produce a volume of which takes up 50x the volume of the original hydrogen peroxide. a) What percentage hydrogen peroxide would represent 1 volume i.e. the produced would take up the same volume as the reactant. 15%/50 = 0.3% In BLOODHOUND SSC the hydrogen peroxide used it at 86% (at this percentage hydrogen peroxide is called high-test peroxide or HTP). b) Calculate the relative volume of the produced compared to the volume of the reactant when the HTP used in the BLOODHOUND SSC rocket engine decomposes. 1% = 50/15 (50/15) x 86 = 860/3 rounded to 287 volume 4. The decomposition of hydrogen peroxide releases a large amount of heat into the surrounding environment. Is the reaction endothermic or exothermic? Exothermic In fact, in BLOODHOUND SSC the decomposition of hydrogen peroxide releases so much energy that the water produced is in the form of steam. 5. The rapid decomposition of liquid hydrogen peroxide within the rocket engine into two gasses propels the car forward. a) How does this happen? Consider physics (especially Newtons 3 rd Law of motion) The gasses are pushed out of the exhaust of the rocket at high speed and by Newtons 3 rd Law (every action has an equal and opposite reaction) this in turn propels the car forward.

11 b) Draw a diagram to illustrate the forces acting on the rocket when it fires Normal Air resistance Rocket pushes on air Air pushes on rocket (thrust) Gravity Friction

12 Extension activity The experiment performed gave a qualitative result. Design an experiment to measure the rate of reaction of the decomposition of hydrogen peroxide quantitatively. Predict the results of your experiment and draw any relevant graphs. The experiment performed as above but without any washing up liquid. Instead, the top of the measuring cylinder would be covered and there would be an escape for any gasses into a syringe (set to 0ml at the beginning of the experiment). As the reaction progresses gas would be produced and collected in the syringe. The volume of gas produced can then be recorded at various time intervals and these results can be plotted on a graph e.g. A graph to show the rate of gas production from the deomposition of hydrogen peroxide with various catalysts Volume of gas produced (ml) Time (seconds) MnO2 PbO2 CuO Liver Boiled liver No catalyst The average rate of reaction in the presence of each catalyst can then be determined by calculating the slope of the line for each catalyst e.g Average rate of reaction for Pb = (Y 2 Y 1 ) / (X 2 X 1 ) = (47 0) / (60 0) = 0.78 ml/sec

Catalysts The effect of various catalysts on the rate of decomposition of hydrogen peroxide (H2O2)

Catalysts The effect of various catalysts on the rate of decomposition of hydrogen peroxide (H2O2) This content is aimed at KS3/4 students and is a two lesson worksheet (including a practical demonstration)