Beatty 6. R1 6092 Decomposition of Hydrogen Peroxide_Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: ________________ Class: 4E___ Practical 6: R1 – Decomposition of Hydrogen Peroxide Skills: MMO: Manipulation, measurement, and observation PDO: Presentation of data and observations ACE: Analysis, conclusions and evaluation P: Planning Aim: To investigate the speed of decomposition of hydrogen peroxide using different metal oxides Apparatus and chemicals: apparatus setup shown in diagram 50 cm3 measuring cylinder stopwatch spatula hydrogen peroxide (3%) powdered manganese(IV) oxide powdered iron(III) oxide Procedure: Hydrogen peroxide decomposes into water and oxygen gas according to the equation below: 2H2O2 → 2H2O + O2 This reaction is greatly speeded up by the use of catalyst. In this experiment, you are going to find out how the speed of reaction is affected by the different types of catalyst, using the apparatus shown below: 25

2 1 Set up the apparatus as shown in the diagram. 2 Use a measuring cylinder to place 50 cm3 of hydrogen peroxide solution in the conical flask. 3 Measure out 0.2 g of manganese(IV) oxide using a piece of recycled paper. 4 Tip the manganese( IV) oxide into the flask and quickly re -insert the rubber bung. Start timing immediately. 5 Gently swirl the flask while recording the volume of gas collected in the gas syringe every 10s. Do this until 120 cm3 of oxygen gas has been collected or 2 minutes. Take care not to undo the rubber tube connector. Record your results in an appropriate table. 6 Repeat steps 2 to 5 using 0.2 g of iron(III) oxide. Results: (a) Record the results for the above experiment in an appropriate format in the space provided below. time interval / s volume of oxygen gas collected using MnO2 catalyst / cm3 volume of oxygen gas collected using Fe2O3 catalyst / cm3 0 10 20 30 40 50 60 70 80 90 100 110 120

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4 (b) On the same axes, plot a graph of volume of gas evolved against time, for both reactions, labelling each one clearly. [4]

5 (c) From the graphs, draw your conclusions on the effect of different metal oxides on the speed of decomposition of hydrogen peroxide. MnO2 helps to speed up the decomposition of H 2O2, whereas Fe2O3 does not speed up the decomposition of H2O2. (d) State three conditions which were kept the same in both experiments to ensure that any differences in the results of the two-experiments were due only to the different amount of catalyst used. Concentration of H2O2, volume of H2O2, temperature of the reaction mixture, particle size of the catalyst used (e) Identify one key source of error and state how it affects your results. Human reaction time due to the delay in s