Investigating Combustion using Gas Sensors
Paul Preece - Camborne Science and Community College
Introduction
The world in which we live is changing rapidly as we move towards a more
technologically advanced society. As teachers it is our responsibility to
prepare pupils for the ever changing demands of the digital world and
ultimately for future employment in jobs that currently do not exist. But this
is not the only reason we need to include ICT in our lessons.
Pupils are already computer literate by the time they arrive in year 7, so
science teachers need to embrace the opportunities provided by data-logging
to develop higher order thinking skills, thus enhancing and deepening pupils’
learning of science. .
For us to develop the higher order thinking skills of applying knowledge,
analysis and synthesis we need to provide opportunities for pupils to draw
conclusions based upon the data they have generated. In some cases the only
(or best) way to do this is by using data-loggers.
However, in order to interpret the data the pupils need to produce graphs
and this is often a huge barrier to pupils getting to the interpretation stage.
Graphing is a valuable skill, but also a difficult technique to master for most
pupils, especially at KS3. So when the objective of the lesson is to interpret
and not specifically the graphing skill then let the data-logger do the work so
that the learner can move easily from the collection of data to the
interpretation of the data, and potentially onto the application of knowledge
to different situations.
This case study focuses on how a combination of sensors - oxygen, carbon
dioxide, humidity - can be used to investigate the combustion process.
Although the specific details of the setup of the sensors is omitted a
description is provided of how ICT can be used to unlock the potential of the
learners by removing some of the barriers to them practising their
application, analysis, synthesis and evaluation skills. For the setting up please
consult your manuals, as this varies for different suppliers.
Investigating Combustion
Curricular Context
This is a more demanding experiment because it uses three sensors. Prior
experience of setting up and using the sensors is advisable. This activity
addresses the Combustion part of the KS4 syllabus.
 It is difficult to teach the combustion equation and the need for oxygen in
combustion. This activity shows how the amount of oxygen in the air
determines how well a fuel combusts. The production of carbon dioxide is
often forgotten by the pupils so this can be addressed by this activity.
 It works on many levels. It can kept as a simple demonstration for lower
achieving students or for establishing and justifying the equation for
combustion with the more able.
ICT approach
Combustion is a process which is taught throughout KS3 and KS4. When
pupils are asked “if a candle was placed in a bell jar how much oxygen you
would need for combustion to occur?” they would probably say “when the
oxygen runs out!”
Also if you asked what is also produced along side heat and carbon dioxide
they would (in most cases) not mention water. By using oxygen, carbon
dioxide and humidity sensors it is possible to demonstrate that with
approximately 16% oxygen in the air the candle will go out and that water
and carbon dioxide are produced.
This visual demonstration shows in real time how the oxygen is ‘used up’ and
the ‘carbon dioxide is produced’ as one line drops the other increases. This
provides the opportunity to establish that the oxygen is being used to react
with the fuel and released as carbon dioxide. But if a humidity sensor is also
available the humidity will increase during the time that the candle is burning
indicating that water is also produced during combustion. As the quantity of
oxygen approaches around 16% the candle flame reduces in size and
eventually goes out. At this point combustion ceases and the oxygen level
stops going down also the humidity also stops increasing therefore linking the
use of oxygen and production of water when combustion occurs.
Method
Equipment needed:
Large bell jar, rubber bung with notches to allow the wires for the sensors to be
fed through but keeping it almost air tight, humidity sensor, oxygen sensor,
carbon dioxide sensor and a candle.
Pupil activity
Pupils share their thoughts as to what
will happen when the candle is lit.
This provides the opportunity to test
the pupils’ knowledge of the process of
combustion.
Teacher activity
Set up the experiment with the data
logger ready to plot in graph. mode the
amount of oxygen , carbon dioxide and
humidity. Discuss with the pupils the
purpose of the apparatus and set the
graph plotting without the candle lit.
Ask the pupils to describe what will
happen to the levels when the candle is
lit.
Set the candle burning and give the
pupils time to see that the oxygen level
is dropping and the carbon dioxide level
is increasing. Then ask the question
when will the candle go out?
Once the candle has gone out indicate
that the oxygen level does not have to
be 0% for the combustion to occur.
Get pupils to write the combustion
equation and justify from their results
how they know what the products are
and what the reactants are. Pupils can
write on the worksheet to aid this
process. There are two pages, one
with the word equation and the other
with the formula equation.
Introduce the combustion equation and
show that the fuel and oxygen are used
up (reactants) since they go down and
that the carbon dioxide levels and
humidity goes up which means that they
are produced products.
For higher students you could reverse
the argument and ask them to suggest
what would happen if a plant was
placed in the bell jar filled with a high
percentage of carbon dioxide and
humidity (compared to normal levels).
Benefits of the approach
 Since the pupils cannot see the particles involved in combustion they find
it difficult to grasp what is going on. Also combustion is complicated
equation to teach and pupils often find it difficult to remember the
reactants and the products. This is a visual way to demonstrate that
combustion really does use oxygen and produce water and carbon dioxide.
 The sensors show in real time that when combustion occurs that reactants
are used and products are produced and data is produced to represent this.
It provides an opportunity for the teacher to embed the process of
combustion by relating the equation to real results. .Pupils then have a
greater appreciation of what the equations represent.
 The pupils can see for themselves what happens rather than relying upon
teacher knowledge.
Note to teachers
This document was not created by Teachers TV but the author has allowed us to publish it
here to be used for educational purposes