Performing the Demonstration
A short piece of Mg ribbon can be burned by placing it in a propane flame. Once the reaction begins, the metal does not need to be held in the flame.
Hold the Mg with a pair of tongs and put a metal bin underneath it as you hold it up to catch the MgO and Mg
Notes About What's Going On
The chemical equations for the this combustion, when carried out in air, are as follows:
2Mg + O
-> 2MgO + heat and light
3Mg + N
+ heat and light
When magnesium burns in air, two chemical reactions occur, both of which can be called addition reactions of the form A + B -> C
) forms about 21% of air and nitrogen forms about 78% of air
A full 10% of the energy released in this reaction is released as light, this is a large percentage compared to the burning of wood; this is why Mg is used in flash bulbs
Even so, the temperature of the metal as it burns is 1335°C!
At the start of the reaction the Mg is electrically neutral; the reaction causes the metal to lose two electrons to become Mg
What are the charges on the atoms that Mg combines with at the end of these reactions?
As always, no one but a trained chemist should perform this demonstration.
As noted above, this metal burns at a
high temperature; do not allow it to burn near anything else that is flammable
Do not allow the ashes to fall onto anything flammable
Warn onlookers not to look at the burning Mg for more than a few seconds at a time; UV eye protection is recommended
Once the ashes are cold they can be disposed of in the trash
Approximate temperature (°C)