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

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1 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) to introduce and study catalysts.

2 Teacher Information BLOODHOUND context and topic introduction This activity relates to the use of a silver plated nickel mesh in the rocket engine for the BLOODHOUND SSC to catalyse the decomposition of HTP (High Test Peroxide, i.e. hydrogen peroxide at roughly 86% concentration). In the BLOODHOUND SSC one method of propulsion is a hybrid rocket engine using a solid state fuel (hydroxyl-terminated polybutadiene, HTPB) and a liquid fuel (HTP). This is an artists impression of the rocket that will be used by BLOODHOUND SSC. The solid black material in the centre is HTPB and the liquid surrounding it is HTP In order to increase the rate of reaction HTP is passed through a silver plated nickel catalyst. This experiment is a demonstration which will explore the effect of various catalysts on the rate of decomposition of hydrogen peroxide.

3 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 include elements of mathematics, physics and biology. Possible differentiation: All students should understand that catalysts can be used to increase a rate of reaction. They should also understand that catalysts are neither reactants nor products and are not 'used up' during the reaction. Most students should explore how to improve the fairness, accuracy and reliability of the experiment. Some students will understand that catalysts provide an alternative pathway for a reaction with a lower activation energy and why this increases the rate of reaction. Key Vocabulary: Reactant Product Catalyst Rate of reaction Reaction pathway Activation energy Endothermic / Exothermic reaction Qualitative / Quantitative experiment

4 Lesson 1 Starter activity: Find the correct answer from the 3 options given Question Answer What is present at the start of every chemical reaction? reactant oxygen catalyst H2O2 is better known as water hydrogen peroxide hydrogenated oxygen Repeating an experiment many times would make the result more reliable safe accurate Oxygen atoms in the air are mostly found in the form of O CO2 O2 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 This activity can be given to each student to answer individually, in groups or even as a class vote.

5 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 (MnO2) Catalyst 2: 0.5g lead(iv) oxide (PbO2) Catalyst 3: 0.5g copper(ii) oxide (CuO) Catalyst 4: 1cm3 liver Catalyst 5: 1cm3 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. The expected result would be that the hydrogen peroxide will decompose into water and oxygen. The oxygen will form bubbles in the washing up liquid and foam will rise in the measuring cylinder. Some of the measuring cylinders may overflow, this makes the demonstration more engaging and should not be a problem as the overflow will collect on the tray. The reaction catalysed by lead oxide is expected to be 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 are expected to produce very little foam (possibly none at all) but it is important to point out that the reaction is still happening just at such a slow rate that it is almost unobservable. It is possible to test the contents of the gas bubbles formed by placing a glowing splint in the foam. The splint should relight in the presence of the oxygen.

6 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 (H2O2). H2O2 + H2O 2. What effect do you predict the presence of a catalyst will have on the rate of reaction? 3. What is the independent variable? 4. What is the dependant variable? 5. What do you expect to see? Remember; the washing up liquid is not reactant, it is only there to help visualise the reaction. Post-demonstration questions 6. What did you observe? 7. Was the result as you predicted? If not, why not? 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. 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. b) The chemical equation for the reaction was 2H2O2 + Catalyst 2H2O + O2 c) The chemical reaction for the reaction was 2H2O2 Catalyst 2H2O + O2 d) Washing up liquid was used in the experiment but was not a reactant, it was only there to visualise the gas production. e) In the reaction without a catalyst the reaction still happened, just at a much slower rate. f) The independent variable in the experiment was the type of catalyst present. g) All the catalysts sped up the rate of reaction by the same amount. h) O2 and H2O were the products in each reaction, just different amounts were produced in the specific time. i) The liver contained a biological catalyst (enzyme) which was almost completely denatured (the functionality was lost) by boiling.

8 Activation energy Shown below is a reaction coordinate diagram. Energy Reactants Products Reaction path A catalyst increases the rate of reaction by offering the reaction an alternative pathway with a lower 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.

9 Energy distribution Number of Particles Below is a graph showing the energy distribution of the atoms in the hydrogen peroxide solution. Energy The area shaded orange shows the particles of hydrogen peroxide with sufficient energy to overcome the activation energy barrier. 2. On the energy distribution diagram above draw how the graph would change in each of the following situations: a) b) 3. The reaction is performed at a higher temperature The reaction is performed in the presence of a catalyst 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 how much volume the products take up when compared to the reactants (at standard room temperate and pressure) i.e. hydrogen peroxide at 15% decomposes into O2 and H2O which take up 50x the volume of the original hydrogen peroxide. a) What percentage hydrogen peroxide would represent 1 volume i.e. the products would take up the same volume as the reactants.

10 In BLOODHOUND SSC the hydrogen peroxide used it at 86% (at this percentage hydrogen peroxide is called high-test peroxide or HTP). b) 4. Calculate the relative volume of the products compared to the reactants when the HTP used in the BLOODHOUND SSC rocket engine decomposes. The decomposition of hydrogen peroxide releases a large amount of heat into the surrounding environment. Is the reaction endothermic or 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 3rd Law of motion) b) Draw a diagram to illustrate the forces acting on the rocket when it fires Extension activity 6. 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.

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

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