Planning an experiment &
writing an experimental report
Plan
When you are planning your experiment you
should
• explain what you are trying to find out – this is
the AIM of the experiment.
Remember to mention what you are changing and
what you are trying to find out.
Plan
• make sure the experiment is FAIR by
changing only one variable – the is called
the input variable or independent variable
• all the other variables should be
unchanged – we say these are the
controlled variables
Plan
• decide what you are going to MEASURE
as the result of the experiment – this is
called the outcome variable or dependent
variable
Plan
• Use a ruler and a pencil to draw a
LABELLED DIAGRAM diagram of the
experiment
• Describe of how you will carry out your
experiment and make sure you include
any additional equipment or chemicals
which you have not included in your
diagram.
Safety
• Before you start your experiment you
should discuss your plan and safety
considerations with your teacher.
• While you are carrying out experiments
your teacher will check that you are
working safely.
Results
• During the experiment you should record
your observations/measurements/results
• Tables of results should be drawn using a
ruler and pencil. The table should have
suitable headings and units.
Results
• Graphs should be plotted on squared graph
paper again using a pencil and a ruler.
• The input variable (what you changed) should
go along the x-axis and the outcome variable
(what you measured as the result of the
experiment) should go along the y-axis.
• Use a ruler to draw a line of best fit or draw a
curve of best fit as best you can.
Conclusion
• Your conclusion should mention the
connection (if any) between the input
variable (what you changed) and the
outcome variable (what you measured as
the result of the experiment).
Evaluation
• Look at the results – are they as you expected? Maybe you could
have done something differently.
• How could you improve your experiment?
• Did you control all the variables so you only changed one thing?
• Did you plan your experiment correctly to allow you to investigate
what you intended to investigate?
• Did you use the correct equipment?
• Was the equipment available to you accurate enough to allow you to
measure accurately?
• Was there some factor which you found difficult to control?
Example of Pupil Plan
The task set:
• When acids react with (neutralise) alkalis, heat energy is
released and a rise in temperature can be observed.
• You are being asked to investigate how the
concentration of acid affects the size of the temperature
rise.
What are the input variable and outcome variable for this
task?
Example of Pupil Plan
concentration of acid = input variable
size of the temperature rise = outcome variable
Example of Pupil Plan
Plan
• I am only going to change the
concentration of the acid.
•
I will use 1 mol/l hydrochloric acid, 1.5
mol/l hydrochloric acid and 2 mol/l
hydrochloric acid.
Does this alter what the correct variable?
Example of Pupil Plan
Plan
Yes, this is correct so far.
The concentration of the acid is going to be
altered.
concentration of acid = input variable
Example of Pupil Plan
Plan
I will keep everything else the same
•
•
•
•
•
Same type of acid (hydrochloric acid)
Same volume of acid (20cm3)
Same type of alkali (sodium hydroxide)
Same concentration of alkali (2 mol/l)
Same volume of alkali (20cm3)
Is this list complete?
Example of Pupil Plan
Plan
Yes, all the controlled variables are listed.
Example of Pupil Plan
Measurements/observations
Which is the best?
(a) I will measure the temperature rise
(b) I will measure the temperature before and then
measure the temperature after 10 minutes
(c) I will use a thermometer to measure the
temperature before mixing the acid and alkali
and measure the highest temperature after the
chemicals are mixed
Example of Pupil Plan
Measurements/observations
(a) you need to subtract so that you can ‘calculate’
the temperature rise. You can ‘measure’ the
temperature but not the temperature rise.
(b) you need to be sure the reaction has taken
place. The reaction may be over and the
products cooling down after 10 minutes.
(c) is the correct and it also clearly states a
thermometer will be used
temperature rise = the outcome variable
Example of Pupil Report
Which is best?
(a) Aim - to find out how the concentration of the
acid affects the temperature
(b) Aim - to find out how the concentration of the
acid affects the temperature rise
(c) Aim - to find out what affects the temperature
rise.
Example of Pupil Report
(b) is the best answer
(a) uses temperature rather than temperature rise
(b) mentions links both what is being altered (the
concentration of the acid) to what is being
observed (the temperature rise)
(c) does not mention what is being altered.
Example of Pupil Report
Method
20 cm3 2 mol/l sodium hydroxide was added
to a small beaker and the temperature
noted.
20 cm3 2 mol/l hydrochloric acid was added
to the beaker of alkali.
Example of Pupil Report
Method
The highest temperature was noted.
Which is the correct diagram?
Example of Pupil Report
Method
The first is a picture showing 3 dimensions.
The second is best. It is a 2 dimensional
drawing showing a ‘slice through’ the
apparatus.
Example of Pupil Report
Method
The experiment was repeated using 1.5
mol/l hydrochloric acid then 1 mol/l
hydrochloric acid.
Is this correct?
Example of Pupil Report
Method
Yes.
Only the concentration of the acid is being
altered.
concentration of acid = input variable
Example of Pupil Report
Results
Concentration of
acid (mol)
Temperature before
(°C)
Temperature after
(°C)
Temperature rise
(°C)
2
22
28
6
1.5
21.5
26
4.5
1
22
24.5
2.5
Is this correct?
Example of Pupil Report
Results
Concentration of acid (mol)
Temperature before (°C)
Temperature after(°C)
Temperature rise (°C)
2
22
28
6
1.5
21.5
26
4.5
1
22
24.5
2.5
The table has clear rows and columns.
The headings are correct.
All the raw results (the readings from the thermometer) are
given.
The temperature rise is correctly calculated each time.
The units for concentration should be mol/l not mol.
Example of Pupil Report
Results
Is this correct?
Example of Pupil Report
Results
The student chose to change the concentration of the acid (the input
variable). This is along the x-axis which is correct.
The scale along the x-axis is not even. the distance between 1 and
2 is twice as long as teh distance between 0 and 1.
There are no units up the y-axis.
It should say °C
The first point is plotted at 2.4 instead of 2.5.
The crosses used to plot the points should be smaller and drawn
with a SHARP pencil.
Example of Pupil Report
Conclusion
The concentration of the acid does affect the size
of the temperature rise.
Is this correct?
Example of Pupil Report
Conclusion
No. The conclusion is too vague. It dos not
give a direction.
It should be:
The higher the concentration of the acid the
higher the temperature rise.
Example of Pupil Report
Evaluation
The thermometer used had 1°C gradations.
Using a thermometer with 0.1°C gradations would have allowed the
temperatures to be measured more accurately.
Only the temperature of the alkali was measured before mixing the.
Measuring the temperature of the acid before the experiment too
and averaging the starting temperatures would have been more
accurate.
Repeating the experiment several times and calculating an average for
each concentration of acid used would give more reliable results.
Some of the heat energy as lost to the surroundings. Insulating the
beaker would have reduced the heat lost.
Are each of these valid?
Example of Pupil Report
Evaluation
Yes, all the suggestions are valid.