INVESTIGATION 8.
9
Changing the rate of reaction
STUDENT LABORATORY NOTES
Introduction
We have seen that chemical reactions can be fast, like an explosion, or slow, like the weathering of
rocks. But the speed (or rate) these reactions occur at can sometimes be manipulated or changed, by
scientists to make a reaction speed up or slow down. There are several ways this can be done, and in
this investigation, you will have the opportunity to design an experiment to see how changing
different variables may have an effect on the rate that the reaction occurs. These variables include the
concentration, or amount of substance that is actively reacting, or how changing the surface area may
change the rate of reaction.
Plan your investigation carefully, remembering that only one variable should be tested at a time.
Aim
To investigate the factors that affect the rate of chemical reactions
Hypothesis
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Preparation for task
Location to conduct this task
In the laboratory
Duration
40 minutes
Group size
2 students (however, 1–4 would be acceptable, depending on class size and resources)
Methodology
Materials (per group)
spatula
heatproof mat
0.5 M hydrochloric acid
test tubes and test-tube rack
1 M hydrochloric acid
white chalk
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measuring cylinder
mortar and pestle
Health and safety guidelines
gloves
safety glasses
lab coat
Method
Hydrochloric acid reacts with chalk to produce carbon dioxide gas, water and calcium chloride.
1. Place a small amount of chalk in a test tube and add enough 0.5 M hydrochloric acid to cover it.
Observe the chemical reaction.
2. Discuss with your partner how you could use this reaction to demonstrate one of the hypotheses
below.
Increasing the concentration or amount of reactants will speed up a chemical reaction.
Increasing the surface area of reactants will speed up a chemical reaction.
Decreasing the concentration or amount of reactants will slow a chemical reaction.
3. Design your experiment and write down the method.
4. Perform the experiment.
Results
1. Predict the results you would expect to obtain that would support the hypothesis you chose.
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2. Record your results.
Discussion
1. Did your prediction prove to be true? Explain.
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2. How could you improve on the investigation you performed?
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Conclusion
Prepare a report of your findings.
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