Based on this illustration and your understanding of composition (synthesis) reactions do you think that the residue that remains weighs more than the initial ribbon? Why or why not?
The demonstration will be repeated but this time the mass of the initial ribbon and the final residue (magnesium oxide) will be measured.
Mass of initial ribbon:
Mass of residue (magnesium oxide):
What do you notice?
How do you explain the mass of the residue is actually much less than what we might have been expected?
Your teacher will take you through a sequence to determine what the theoretical yield of magnesium oxide for this amount of initial ribbon might have been. Note that in terms of particles reacting, the equation tells us about how many particles of each reactant are required to produce the magnesium oxide product. Remember, it is the number of particles available that determines how much product can form.
Part B: Extending the Demonstration into an Investigation:
As you might have expected most of the magnesium oxide produced when the magnesium burns is released into the air. If we could capture this reaction in a closed vessel we might expect that the mass of the residue is indeed grater than that of the initial magnesium. A crucible is quite resistant to heat and will be used in this investigation. The crucible has a lid which can contain the reaction reducing loss of the product.