C1.13a Electrolysis: Student brief Practice Controlled Assessment This practice controlled assessment is about electrolysis of acids. Hydrochloric acid is made by reacting hydrogen and chlorine together to form hydrogen chloride. This forms a gas when it dissolves in water. Substances such as hydrochloric acid can be broken down using electrical energy. This process is called electrolysis. You are going to test the hypothesis that all acids release hydrogen gas when they undergo electrolysis. Plan an investigation to test what happens when an electric current is passed through a range of acids.
Part A: Planning How to attempt the task: You must produce a plan. The plan must include: •
an explanation of which equipment you need to complete the task. You may want to draw a diagram of how the equipment will be set up
•
which variable (or variables) you will change and which you will keep the same
•
which measurements you should make to test the hypothesis, explaining how these will test the hypothesis, and including the number and range of measurements
•
any risks that are linked to the practical task and how you can reduce these to make your practical task safer.
You should check that the overall plan is clear and will produce a range of results that will test the hypothesis.
Part B: Observations You are going to test the hypothesis that all acids release hydrogen gas when they undergo electrolysis. You will test this hypothesis using your own method from Part A. You should also collect some secondary evidence on electrolysis of acids.
How to attempt the task: You should decide on the number and range of measurements you will make Complete the practical task, recording your measurements clearly and accurately Collect some secondary evidence on this task Comment on the quality of the source of this secondary evidence.
Part C: Conclusions You will need your primary and secondary evidence from the Part B: Observations task and information about the method you used.
How to attempt the task: You must process your primary and secondary evidence from Part B and present these, using mathematical processes if relevant. You must produce a conclusion in which you: •
review all of the primary and secondary evidence, then identify and deal with any anomalies
•
draw conclusions from this processed evidence to prove or disprove a hypothesis
•
show how the data supports the conclusion
•
explain how you might change the method if you were going to repeat the investigation
•
describe the primary and secondary evidence you might collect to extend your investigation and say why you would collect it.
© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
C1.13b Electrolysis: Observations Practice Controlled Assessment You are going to test the hypothesis that all acids release hydrogen gas when they undergo electrolysis. You will be given the following equipment/resources: A range of acids, beaker, ignition tubes (very small test tubes), test tube holder, power supply, electrodes, connecting wires and crocodile clips, Bunsen burner, heat resistant mat, splints, eye protection.
Health and Safety Take care with acids. If any spills onto your skin wash it off immediately with cold water. Wear eye protection. Take care with power packs and setting up circuits. Do not touch electrical equipment with wet hands. Mop up any spills immediately. Do not run the electrolysis circuits for too long and keep the room well ventilated. Do not breathe in any of the gas given off from the electrodes. Chemical-resistant gloves will be needed when installing the test tubes into the acids. Follow these instructions when carrying out the practical: 1
Set up the apparatus as shown in the diagram. test tubes to collect gases electrode covered in plastic
metal
hydrochloric acid
2
Put the acid you are testing into the beaker. The ends of the electrodes should just be covered.
3
Set the power supply to 6 V. Switch on and leave it for 5 to 10 minutes
4
Switch off the power supply.
5
Test the gases you have collected.
6
Repeat steps 1 to 5 for the other acid.
Š Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
C1.13c Electrolysis: Recording results Practice Controlled Assessment Name
Class
Date
Carry out the investigation on Worksheet C1.13b Electrolysis: Observations and use this sheet to record your results and draw a conclusion.
Recording your results 1
Record your data in this table.
Substance tested
Observations
Presenting data 2
a
Summarise your data in a way that helps you to work out whether or not your observations support the hypothesis.
Š Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
Sheet 1 of 2
C1.13c Electrolysis: Recording results Practice Controlled Assessment
Considering your results/conclusions 3
What pattern can you see in your observations?
4
Suggest a reason for the pattern.
Evaluation 5
How good was the quality of your data? Explain your answer.
6
Did you reach the same conclusion as other groups? Suggest a reason for any differences in the observations made by different groups.
Š Pearson Education Ltd 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
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