04. Burning magnesium
What happens to the mass of magnesium when it burns?
When magnesium burns in air there is a very bright flame and white smoke.
Ash is formed. Usually the smoke rises up in the air. In this experiment you
will try to catch all the smoke and ash, to find out how much is produced.
Predicting
When magnesium is heated, there are three possible things that could
happen to the mass:
The white ash will have a higher mass than magnesium.
The white ash will have a lower mass than magnesium.
The mass of the magnesium and the ash will be the same.
1 Write down your prediction.
2 Explain your prediction
Apparatus
eye protection
a strip of magnesium
tripod
crucible and lid
gauze
Bunsen burner
heatproof mat
sandpaper
tongs
Method
A Measure the mass of the crucible with the lid. Write it down.
B Take the strip of magnesium. Make sure that it is shiny and silver. If it needs cleaning, use a piece of sand paper to clean off any coating.
C Coil up the magnesium so that it fits inside the crucible. Try not to coil it too tightly, so that the air will be able to get to all parts of the metal.
D Put the coil of magnesium inside the crucible, and put the lid on. Measure the mass of the crucible and magnesium together. Write it down.
E Put the crucible into the pipe-clay triangle, and support this on the tripod, as shown in the diagram. Leave the lid off at the start.
F Heat the crucible with a strong blue Bunsen flame.
G When the magnesium starts to burn, use the tongs to put the lid onto the crucible. This will stop the smoke escaping.
H About every 10 seconds, using the tongs, lift up the lid to let some air in. Try not to let any smoke out.
I When you think that all the magnesium has burned, take the lid off and keep heating until you are sure that there are no more sparks or flames. If more smoke is given off, you should put the lid back on again.
J When the reaction is finished, turn the Bunsen burner off.
The crucible will be very hot! Leave it for at least 5 minutes to cool down.
K Measure the mass of the crucible with the ash in it. Don’t forget to put the lid on! Write it down.
Recording your results
3 Design a table to record your results.
Considering your results/conclusion
4 What has happened to the mass of the magnesium in your experiment? Has it gone up or down?
5 Using your results alone, can you be certain that this is the right answer? Why?
6 a Compare your answer with the other groups in the class. Display the class summary results in a suitable chart or table.
b Is it a good idea to use everyone’s results? Explain why it might be helpful to work out an average.
7 Using the class results, can you be sure about whether the mass of magnesium has gone up or down. Why?
8 Was your prediction correct?
9 a What has the magnesium reacted with?
b What chemical has been formed?
10 a Write a word equation for the reaction.
b How does this equation help to explain your results?
Evaluation
11 Suggest why different groups might have got different results. What mistakes might have been made? Give reasons for your suggested changes.
12 Can you suggest improvements to the way the experiment was done to make the results more accurate?