YEARS 7–12 IDEAS FOR THE CLASSROOM
Year 7 Practical Skills for Inquiry Learning (continued)
Some teachers choose to make these up to look like driving
licences – if a student behaves stupidly when using a Bunsen
then his/her licence is withdrawn (perhaps a hole punched in it?)
and they are not allowed to take part in practical activities for a
prescribed length of time.
Now open the air hole fully (the ‘open’ flame) and write down
as many observations of this flame as you can. Draw a labelled
diagram of this flame too.
2. Hold a piece of porcelain in metal tongs and place it just above
the ‘closed’ flame for a short while. Record any observations
in your journals. Repeat with the ‘open’ flame. (This does not
always work very well so you may decide not to bother).
Differences between two Bunsen burner flames
The simple experiments below allows students to explore the
two flames and practise using Bunsen burners, adhering to the
safety precautions you have discussed with them – only those for
lighting the Bunsen, keeping it on a heat mat, putting anything
hot onto the heat mat, not handling hot things(!) and turning off
(or onto the ‘safety flame’) when not in use In the first experiment
students will explore the two main Bunsen burner flames. You
must decide whether you can give each group matches, whether
‘lighters’ would be safer, or whether you need to light all the
Bunsens.
Write a list of differences between the two flames.
For the teacher:
Give the students plenty of time to do these tasks but try not to tell
them anything – encourage their ideas, and ask questions to help
them think things through. Watch for anyone mucking about with
the Bunsen and sit them down away from the practical – important
to be firm about this from the start. When a couple of groups have
finished get them together to share their ideas and so on, until all
have finished. Results can then be shared in a class discussion.
Results:
Requirements: per group
• Bunsen burner
• heat mat, matches or ‘lighter’
• metal tongs, wooden pegs
• wire gauze
• unlit match + sewing pin
• thick-walled glass tube (i.e. hollow) about 12-14cm long, ~
6-7mm wide
• safety glasses
• test tube
1.
• a wavy flame
• quiet
• yellowy colour
• much smoke and black
bits (carbon)
• burns the gas in
surrounding air
• steady flame
• noisy
For the students:
• ‘transparent’; pinky blue
round the edges
If possible let students work in the same pairs as before if you
have the necessary apparatus and gas taps – otherwise use the
smallest number in as group as is possible. Perhaps forgo the
role cards and ask them to share the practical work between
them (keep an eye out to see that this happens!)
• bright blue ‘inner cone’
• no smoke
• gas already mixed with
lots of air
You can either explain what their tasks are or give each pair
written instructions as given below.
2. The porcelain held above the ‘closed’ flame should become
covered with a layer of ‘soot’ - carbon from the incomplete
combustion of the gas in the flame. It is these carbon particles
glowing ‘yellow hot’ which gives the flame its colour and
luminosity. You may like to set students the task of finding out
‘what a flame actually is’ and where the yellow colour comes
from in this instance – especially if they ask questions about
this. Check answers next lesson.
You are going to explore the two different flames which you can
achieve with the Bunsen burner by changing the position of the
air hole. Set up your Bunsen and light it as you have just learned
to do. Your teacher may want to watch you do this (I used to do
this individually with students).
1. Examine the flame you see when the air hole is closed (the
‘closed’ flame) – write down as many observations of the flame
as possible. Draw a diagram of this flame in your science
journal and include any labels you think will help to describe it.
There is no soot deposit when the porcelain is held above the
‘open flame’.
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SCIENCE EDUCATIONAL NEWS VOL 68 NO 1