SCH3U1
The Combustion of Magnesium
Introduction:
Magnesium metal will undergo combustion when heated:
magnesium metal +
oxygen
magnesium oxide
In this lab, you will carry out a carefully controlled combustion reaction using a piece of
magnesium ribbon. Using a covered ceramic crucible that can withstand high heat,
you will place a piece of magnesium in a crucible and measure the initial mass. After
heating the crucible until the reaction is appears to be complete,, you will heat the
sample using high heat for 1 minute with a Meeker burner. By measuring the final
mass of the crucible and product, you will then calculate the mass of magnesium oxide
that was produced. Some points to consider in your procedure:
• do not get the ceramic crucibles wet since the absorb water
• do not place hot crucibles or other apparatus directly on the lab bench
• be careful not to touch hot objects (e.g. ring clamp, crucible etc.)
• occasionally allow fresh air into the crucible
• avoid letting smoke escape from the crucible
• allow crucibles to cool before weighing
• dispose of the cooled product after the experiment and return all
equipment to the proper location
Purpose:
i) To observe the properties of magnesium and magnesium oxide.
ii) To determine the percentage composition of magnesium oxide
Pre-Lab Questions:
1. State the Law of Conservation of Mass in your own words.
2. Define percentage composition.
Safety:
Describe the safety precautions taken in the experiment.
Materials:
Prepare a list of all materials used.
Diagram:
Draw a labeled diagram of the apparatus from a side view (shown below).
The diagram should be in pencil on blank paper and occupy
approximately half a page. All labels should be placed at the right.
Procedure:
Write a step-by-step procedure for the experiment. It should be detailed enough for
another student to follow and achieve the same results.
Observations:
The following observation should be record in a Table 1:
1. Describe the physical and chemical properties of magnesium.
2. Describe the physical properties of magnesium oxide.
The following observations should be recorded in Table 2:
1. The mass of the empty crucible and cover.
2. The mass of the crucible, cover and magnesium.
3. The mass of the crucible, cover and magnesium oxide.
Calculations and Analysis:
1. Calculate the mass of the magnesium metal.
2. Calculate the mass of the magnesium oxide produced.
3. Using the Law of Conservation of Mass, calculate the mass of oxygen that
reacted with the magnesium.
4. Calculate the % of magnesium in magnesium oxide, based on this experiment.
5. Calculate the % of oxygen in magnesium oxide based on this experiment:
6. What evidence was there that a chemical change occurred?
7. Why must a cover be used to prevent the loss of large amounts of smoke?
8. How would the loss of large amounts of smoke affect your results for the %
magnesium in magnesium oxide (i.e. would it be higher, lower or the same)?
Explain your reasoning.
9. Why is the air used in this experiment is not considered a pure substance?
10. Based on the type of gases that are common in the air, name another product
that may be formed in this experiment.
Conclusion:
Restate the two purposes of the experiment and state your results. State some
possible systematic sources or error that may have affected the results. Discuss any
problems encountered and how the experiment could be improved if it was repeated.
References:
Provide an appropriate citation for any reference materials you referred to.