C1.3a Finding the percentage of oxygen in air: Student brief Practice Controlled Assessment This practice controlled assessment is about percentage of oxygen in the air. Many substances, including metals, react with the oxygen in air. Some metals react quickly and some slowly. For example, when iron rusts it uses up the oxygen in the air. Reactions such as these can be used to find the percentage of oxygen in air. You are going to test the hypothesis that about one fifth of the volume of the air is oxygen. Plan an investigation to test what happens when a metal such as iron reacts with oxygen in the air.
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 about one fifth of the volume of the air is oxygen. You will test this hypothesis using your own method from Part A. You should also collect some secondary evidence on the volume of oxygen in the air.
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.
C1.3b Finding the percentage of oxygen in air: Observations Practice Controlled Assessment Metals react with oxygen in the air. Some react slowly and some react quickly. By using this reaction you can work out how much oxygen there is in the air. You are going to test the hypothesis that one fifth of the volume of air is oxygen. You will be given the following equipment/resources: 250 cm3 beakers, boiling tubes, glass rod, iron/steel wool, ruler, marker pen, stands, clamps, bosses
Health and safety There are no particular health and safety risks involved in this practical.
How to tackle the task: You should decide on the number and range of measurements you will make. Complete the practical task, recording your measurements clearly and making sure that you produce good quality data. Iron wool Test-tube Beaker
Water
Follow these instructions when carrying out the practical: 1
Wet a piece of iron/steel wool.
2
Place the iron/steel wool in a boiling tube. Use a glass rod to push it down to the end of the tube.
3
Place the boiling tube upside down in a beaker about half full of water and clamp the tube in a fixed position.
4
On the outside of the boiling tube, mark the water level inside the boiling tube using a permanent marker pen.
5
You could set up other tubes in the same way if necessary.
6
Leave the tube for a few days for the iron/steel wool to react with the oxygen in the air.
7
On the outside of the boiling tube, mark the final water level inside the tube with the marker pen.
8
Measure the height of the column of air inside the tube before and after the reaction.
Š Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
C1.3c Finding the percentage of oxygen in air: Recording results Practice Controlled Assessment Name
Class
Date
Carry out the investigation on worksheet C1.3b Finding the percentage of oxygen in air: Observations and use this sheet to record your results and draw a conclusion.
Recording your results 1
Record your results in the table below. Time
Tube number
Before reaction
After reaction
Height of air in boiling tube (mm)
Considering your results/conclusions 2
Calculate the difference in the height of the column of air inside the tube before and after the reaction. This represents the proportion of air that was used up by reaction with the iron/steel wool.
3
Use your answer to 2 to calculate the percentage of oxygen in air.
4
Collect and record the results for at least three other groups. Time
Tube number
Before reaction
After reaction
Tube number
Before reaction
After reaction
Tube number
Before reaction
After reaction
Height of air in boiling tube (mm)
Time Height of air in boiling tube (mm)
Time Height of air in boiling tube (mm)
5
According to your own results, what is the percentage of oxygen in air?
6
Work out the mean value using your results and the results you got from other people. Based on these results put together, what is the percentage of oxygen in air?
Š Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
Sheet 1 of 2
C1.3c Finding the percentage of oxygen in air: Recording results Practice Controlled Assessment Evaluation 7
The actual percentage of oxygen in air is about 21%. Did this investigation provide you with good quality data? Explain your answer.
8
Think about how you measured the height of the air in the boiling tube. Is this a good way to find the proportion of oxygen in the air? Give reasons for your answer.
9
Suggest some strengths and/or weaknesses with the method used in this experiment.
10 How would you improve the way you carried out this investigation? 11 How would this improvement increase the quality of your data?
Š Pearson Education Ltd 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
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