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Topic: Rates of Reaction / Catalysts
Level: Ordinary & Higher Level
Exam Focus: Gas Collection + Catalyst Explanation
1. Experiment Snapshot
Feature
Details
Experiment
To investigate the effect of a catalyst on the rate of decomposition of hydrogen peroxide.
Reaction studied
Hydrogen peroxide decomposes into water and oxygen.
Catalyst used
Manganese dioxide, MnO₂, or sometimes yeast/catalase in school demonstrations.
Main measurement
Volume of oxygen gas produced over time.
Difficulty
⭐⭐⭐ Medium
Exam importance
⭐⭐⭐⭐ Very common for rate, catalyst and graph questions.
2. Aim
To show that a catalyst increases the rate of decomposition of hydrogen peroxide by measuring the volume of oxygen gas produced over time, with and without a catalyst.
3. Quick Theory
A catalyst is a substance that increases the rate of a chemical reaction without being used up in the reaction.
2H₂O₂ → 2H₂O + O₂
Hydrogen peroxide decomposes slowly at room temperature. Manganese dioxide speeds up the reaction by providing an alternative pathway with lower activation energy.
Catalyst → lower activation energy → faster reaction
Examiner Tip: A catalyst is not consumed. It may be recovered at the end, although it may look wet or mixed with products.
4. Apparatus and Chemicals
Apparatus
Chemicals
Conical flask, rubber bung, delivery tube, gas syringe or inverted measuring cylinder, stopwatch, measuring cylinder, spatula, balance, clamp stand.
Hydrogen peroxide solution, manganese dioxide powder, water for gas collection if using displacement method.
Safety: Wear goggles. Hydrogen peroxide can irritate skin and eyes. Manganese dioxide powder should not be inhaled. Oxygen supports combustion, so keep away from flames except for controlled gas testing.
5. Labelled Experiment Diagram
Hydrogen Peroxide Decomposition with Catalyst
6. Variables
Variable Type
In this Experiment
Independent variable
Presence or mass of catalyst.
Dependent variable
Volume of oxygen gas produced per unit time / reaction rate.
Controlled variables
Volume and concentration of hydrogen peroxide, temperature, same apparatus, same time intervals.
Examiner Trap: If comparing with and without catalyst, keep the same volume and concentration of hydrogen peroxide.
7. Procedure
Measure a fixed volume of hydrogen peroxide solution into a conical flask.
Set up the flask with a rubber bung, delivery tube and gas syringe.
Measure a small fixed mass of manganese dioxide catalyst.
Add the catalyst to the hydrogen peroxide and quickly replace the bung.
Start the stopwatch immediately.
Record the volume of oxygen gas produced every 10 or 20 seconds.
Continue until no more gas is produced or the volume becomes constant.
Repeat without catalyst for comparison, keeping all other conditions the same.
Plot volume of oxygen against time for both reactions.
Compare the initial slopes of the graphs.
Examiner Tip: The catalyst speeds up the reaction, so oxygen is produced faster. The final amount of oxygen may be the same if the amount of hydrogen peroxide is unchanged.
8. Results Table Template
Time / s
Volume O₂ without catalyst / cm³
Volume O₂ with MnO₂ / cm³
0
0
0
20
2
22
40
4
36
60
6
43
80
8
46
100
10
47
120
12
47
Conclusion: The reaction with manganese dioxide is faster because oxygen is produced more quickly and the graph has a steeper initial slope.
9. Graph Skills
Graph Feature
Meaning
Steeper initial slope
Faster reaction.
Line levels off
Reaction finished / hydrogen peroxide used up.
Catalysed curve reaches plateau sooner
Same reaction completed in less time.
Same final volume
Same amount of reactant used; catalyst changes rate, not yield.
Typical Catalyst Rate Graph
Examiner Tip: If the same amount of hydrogen peroxide is used, the catalysed and uncatalysed reactions may produce the same final volume but at different speeds.
10. How a Catalyst Works
A catalyst provides an alternative reaction pathway with lower activation energy. This means more particles have enough energy to react at the same temperature.
Exam answer sentence:
A catalyst increases the rate by providing an alternative pathway with lower activation energy, so more successful collisions occur per second.
Catalyst lowers activation energy but is not used up.
11. Gas Test for Oxygen
Oxygen gas is tested using a glowing splint.
Oxygen relights a glowing splint.
Safety: Oxygen supports combustion, so keep flames controlled and away from flammable materials.
12. Sources of Error and Improvements
Source of Error
Effect
Improvement
Gas escapes before bung is fitted
Measured oxygen volume too low.
Fit bung quickly after adding catalyst.
Leak in apparatus
Gas volume too low.
Check connections are airtight.
Different mass of catalyst
Rate comparison unfair.
Use the same measured mass each trial.
Temperature changes
Rate changes because temperature affects particle energy.
Use a water bath or keep room temperature constant.
Gas syringe sticks
Incorrect volume reading.
Check the syringe moves smoothly before use.
Inconsistent timing
Unreliable graph.
Record at fixed time intervals and repeat trials.
13. Student Common Mistakes
Saying the catalyst is used up.
Forgetting that the gas is oxygen.
Using the hydrogen gas test instead of the oxygen gas test.
Thinking the catalyst always increases the final amount of gas.
Not fitting the bung quickly enough.
Changing both catalyst amount and hydrogen peroxide concentration at the same time.
Forgetting to keep temperature constant.
Saying the catalyst gives energy to particles instead of lowering activation energy.
14. Examiner Tips
Tip 1: Define catalyst carefully: increases rate and is not used up.
Tip 2: Oxygen relights a glowing splint.
Tip 3: Catalysts affect rate, not the total amount of product if reactant amount is unchanged.
Tip 4: Graphs with a catalyst have a steeper initial slope.
15. Examiner Traps
Trap: A catalyst is not a reactant, even if it is present in the reaction flask.
Trap: The oxygen test uses a glowing splint, not a lighted splint.
Trap: More catalyst can increase rate up to a point, but it does not create more hydrogen peroxide.
Trap: Same final volume but shorter time means faster reaction, not more product.
16. 🎮 Interactive Simulator: Catalyst Oxygen Lab
Choose Conditions
Oxygen Collection
0 cm³ O₂
Choose conditions, then run the reaction.
Practice Score: 0/0
17. Past Paper Style Questions
State the aim of this experiment. [2 marks]
Define catalyst. [2 marks]
Write the word equation for the decomposition of hydrogen peroxide. [2 marks]
What gas is produced and how is it tested? [3 marks]
Explain how a catalyst increases the rate of reaction. [3 marks]
Why may the final volume of oxygen be the same with and without catalyst? [2 marks]
Give two variables that must be kept constant. [2 marks]
Give one source of error and one improvement. [2 marks]
18. Mark Scheme Answers
Q1. To investigate the effect of a catalyst [1] on the rate of decomposition of hydrogen peroxide / oxygen production [1].
Q2. A substance that increases the rate of reaction [1] without being used up [1].
Q3. hydrogen peroxide → water [1] + oxygen [1].
Q4. Oxygen [1]; test with glowing splint [1]; splint relights [1].
Q5. Catalyst provides alternative pathway [1] with lower activation energy [1], so more successful collisions occur per second [1].
Q6. Same amount of hydrogen peroxide is used [1]; catalyst changes rate, not amount of product/yield [1].
Q7. Volume/concentration of hydrogen peroxide / temperature / same apparatus / same time intervals / mass of catalyst if comparing repeats. Any two [2].
Q8. Gas escapes before bung fitted [1]; fit bung quickly/check airtight apparatus [1]. Other valid answers accepted.
19. Quick Revision Card
Key Point
Memory Hook
Catalyst
Speeds reaction, not used up.
Reaction
Hydrogen peroxide → water + oxygen.
Gas test
Oxygen relights glowing splint.
How catalyst works
Lowers activation energy.
Graph effect
Steeper slope, reaches plateau sooner.
Final volume
May be same if same H₂O₂ amount used.
Main error
Gas lost before bung fitted / leaks.
20. Mastery Checklist
I can state the aim of the catalyst experiment.
I can define a catalyst correctly.
I can write the decomposition equation for hydrogen peroxide.
I can identify oxygen and its test.
I can draw and label the apparatus.
I can explain how a catalyst lowers activation energy.
I can interpret catalyst rate graphs.
I can explain why final gas volume may be unchanged.