3.2.5Physical Chemistry
Practical: Effect of Catalysts on Rate of Reaction — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 7 parts Lesson 14 of 19
Part 1 of 5Aim and background
Aim
- Aim To investigate the effect of different solids on the catalytic decomposition of hydrogen peroxide.
The reaction
- The reaction Hydrogen peroxide breaks down slowly into water and oxygen: 2H2O2(aq) → 2H2O(l) + O2(g).
- The oxygen produced is easy to collect and measure, so its volume is used to follow the rate.
Catalysts to compare
- Catalysts to compare Typical solids are manganese(IV) oxide, copper(II) oxide, iron(III) oxide and lead(II) oxide.
- Each is added as a powder.
Part 2 of 5Variables
| Type | Variable | How it is handled |
|---|---|---|
| Independent | Identity of the catalyst | Change for each experiment, including one run with no catalyst as a control |
| Dependent | Volume of oxygen collected in a set time | Read from the measuring cylinder or gas syringe |
| Control | Volume and concentration of hydrogen peroxide | Measure the same volume of the same solution each time |
| Control | Mass of catalyst and its particle size | Weigh the same mass of powder each time |
| Control | Temperature | Keep the flask at room temperature |
Part 3 of 5Method
1
Measure a fixed volume of hydrogen peroxide solution into a conical flask.
2
Fill a measuring cylinder with water, invert it in a water trough and connect it to the flask with a delivery tube.
3
Weigh a fixed mass of the first catalyst, add it to the flask and close the bung straight away. Start the stopwatch.
4
Record the volume of oxygen in the measuring cylinder at regular intervals, such as every 10 seconds, for a few minutes.
5
Repeat with each catalyst, using fresh peroxide and a clean flask each time, and finish with a run containing no catalyst.
Part 4 of 5Processing and comparing results
1Plot the data
- Plot the data Draw volume of oxygen against time on the same axes for every catalyst, using a different symbol or line for each.
2Compare the gradients
- Compare the gradients The steeper the initial slope, the faster the reaction.
- The best catalyst gives the steepest curve.
3Check the plateau
- Check the plateau All curves should level off at the same total volume, because the same amount of peroxide was used.
4Conclude
- Conclude Rank the catalysts by rate and state that each one changes only the rate, not the amount of oxygen.
Part 5 of 5Safety and evaluation
Safety
- Safety Wear eye protection.
- Hydrogen peroxide can bleach skin and clothes,
- and lead(II) oxide is toxic,
- so wear gloves, avoid skin contact and follow your teacher's guidance on its use.
Catalysts are not used up
- Catalysts are not used up At the end, the solid can be filtered off, washed, dried and weighed again.
- Its mass is unchanged, which shows it was not consumed.
Improvements
- Improvements A gas syringe gives more accurate volumes, and repeating each run lets you identify anomalies and calculate means.
Key terms
| Term | Meaning |
|---|---|
| Catalyst | A substance that speeds up a reaction and is not used up. |
| Decomposition | A reaction in which one compound breaks down into simpler substances. |
| Gas syringe | A calibrated syringe used to measure the volume of a gas produced. |
| Gradient | The slope of a line on a graph; here it shows the rate of reaction. |
| Control experiment | A run without the factor being tested, used for comparison. |
Avoid these mistakes
1
Using different masses of each catalyst. This makes the comparison unfair.
2
Leaving out the no-catalyst run, which is needed to show that the solid really speeds up the reaction.
3
Saying a catalyst produces more oxygen. The total volume is the same; it is just formed faster.
4
Stating that the catalyst is used up. It can be recovered with the same mass at the end.
5
Forgetting to fit the bung quickly, so some oxygen escapes before collection starts.
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