Question

Let the weight of the crucible combined with the weight of the magnesium wire before heating be x, and that of the crucible with the product Magnesium Oxide be y; then which of the following options is correct?
a.) x = y
b.) x < y
c.) x > y
d.) Depends on the element

Answer 1

Hint: The law of conservation of mass plays a crucial part in answering this question. Remember that this experiment is also used in the determination of the empirical formula of Magnesium Oxide.

Step-by-Step Solution:
Let us first analyse the experiment in question.
Measure and record the mass of an empty crucible with its lid.
Put a length of magnesium ribbon into the crucible.
Measure and record the total mass of the crucible, its lid and contents.
Place the crucible on a tripod with a pipe clay triangle. Strongly heat the crucible for several minutes using a Bunsen burner.
Use tongs to lift the lid carefully from time to time. This lets oxygen from the air reach the magnesium.
When the magnesium has stopped glowing, turn off the Bunsen burner and allow the crucible to cool down.
Again, measure and record the total mass of the crucible, its lid and contents.
Now, observing and tabulating the results:

Step	Mass (g)
Mass of crucible and lid (step 1)	50.00
Mass of crucible, lid and magnesium (step 3)	50.24
Mass of crucible, lid and magnesium oxide (step 7)	50.40

From these results, we can safely conclude that the answer to this question is b).

Note: To then use these results to find the empirical formula of MgO, use the following steps:
Calculate the mass of magnesium used:
mass = 50.24 g - 50.00 = 0.24 g

Calculate the mass of oxygen gained during heating:
mass = 50.40 g - 50.24 = 0.16 g

Now, calculate the empirical formula of magnesium oxide (Ar of Mg = 24 and Ar of O = 16)
Your final answer should result in you obtaining this equation:
$$2M{g}_{(s)}+O_{2(g)}\to 2Mg{O}_{(s)}+energy$$