1.3

Question 1

Health & Safety

Answer 1

• The main hazard in this experiment is one of heat. Take care not to touch any apparatus that is hot.
• When observing the experiment, wear safety glasses at all times.
• Take particular care at stages 3 and 4 below.

Question 2

Procedure

Answer 2

1. Measure the mass of the crucible + lid.
2. Put the magnesium ribbon to the crucible. You will need to coil the magnesium so that it fits.
   Reweigh the crucible + lid.
3. Arrange the apparatus as below and heat the crucible strongly.
   Raise the crucible lid slightly using tongs to control the reaction
4. When the reaction is nearly complete, place the crucible lid on the heat-proof mat and heat the crucible strongly for 5 minutes. During this time, tap the magnesium oxide gently with tongs to break up the residue.
5. Allow the crucible to cool and reweigh the crucible, its contents and the lid.
6. Calculate the mass of magnesium that you reacted, the magnesium oxide formed and oxygen that reacted.
7. Calculate the mol of Mg and O atoms in the magnesium oxide that you prepared.
8. Determine the empirical formula of magnesium oxide.

Question 3

1. Why did you need to raise the crucible lid slightly when you first heated the magnesium?

Answer 3

1. To allow sufficient oxygen to enter the crucible

Question 4

2. What was the purpose of breaking up the magnesium oxide whilst heating the contents of the crucible strongly for 5 minutes?

Answer 4

2. To ensure it could fully react with the oxygen available.

Question 5

3. The formula from this experiment often shows slightly less oxygen than is present in magnesium oxide. Suggest why this should be so.

Answer 5

3. Not all of the magnesium may have reacted.

Question 6

4. If magnesium is heated very strongly in pure nitrogen, magnesium nitride is formed. This compound is a black colour and usually a small amount of this compound contaminates the magnesium oxide that is formed in this experiment.
   (a) Why does the magnesium react with oxygen rather than nitrogen?

Answer 6

4. a) oxygen is more reactive than nitrogen

Question 7

(b) 1.82 g of magnesium reacted to form 2.52 g of magnesium nitride. Calculate the formula of magnesium nitride.

Answer 7

b) 2.52 – 1.82 = 0.7 g
1.82 ÷ 24.3 = 7.49 × 10-2 mol 0.7 ÷ 14 = 0.05 mol
Ratio 1.5:1
Scale 3:2
So Mg3N2

Question 8

equipment

Answer 8

Each learner or group will require access to the following
•	safety spectacles (or goggles) 
•	access to balance accurate to two decimal places 
•	crucible
•	Bunsen burner
•	tripod 
•	heatproof mat
•	pipeclay triangle