A student wants to find out whether increasing the temperature of a reaction between marble chips and dilute hydrochloric acid increases the rate of reaction. Describe how the student could carry out a fair test to investigate this, including how the rate of reaction would be measured.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. Keep the mass of marble chips and the concentration of HCl constant for all trials.
2. Make temperature the independent variable – perform the experiment at several different temperatures.
3. Measure the rate of reaction by recording the time taken to collect a fixed volume of CO₂ (or by measuring the volume of CO₂ collected in a set time).
4. Repeat each temperature trial several times and compare the results to draw a conclusion about the effect of temperature on the reaction rate.
2. Make temperature the independent variable – perform the experiment at several different temperatures.
3. Measure the rate of reaction by recording the time taken to collect a fixed volume of CO₂ (or by measuring the volume of CO₂ collected in a set time).
4. Repeat each temperature trial several times and compare the results to draw a conclusion about the effect of temperature on the reaction rate.
Examiner tips
- Use the command word ‘describe’ – list the steps in order. Mention the control variables explicitly. Show how the rate will be measured. State that trials are repeated for reliability.
Common mistakes
- Not specifying which variable is controlled. Using a method that does not give a quantitative rate (e.g. just noting when the reaction stops). Failing to repeat the experiment at each temperature.
Mark scheme (4 marks)
- Keep one variable constant / identify a control variable (e.g. same mass/size of marble chips OR same concentration/volume of acid)
- State that temperature is the independent variable / repeat the experiment at different temperatures
- State a valid method to measure the rate of reaction (e.g. measure the volume of carbon dioxide gas collected in a set time OR measure the time taken to collect a fixed volume of gas)
- State that the experiment should be repeated at each temperature (to improve reliability) OR that results at each temperature should be compared to draw a valid conclusion
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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