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Question 75

When magnesium ribbon is heated in a crucible, it reacts with oxygen in the air to form magnesium oxide, MgO\text{MgO}MgO.

A class of students investigated the relationship between the mass of magnesium heated and the mass of magnesium oxide formed.

Each student was given a different mass of clean magnesium ribbon to heat. The students used the following method:

  • Weigh a crucible and its lid.
  • Place the magnesium ribbon in the crucible, replace the lid, and reweigh.
  • Heat the crucible strongly, lifting the lid from time to time.
  • Allow the crucible and lid to cool and reweigh.
  • Repeat the heating, cooling, and reweighing until two consecutive masses are the same.
  • Calculate the mass of magnesium oxide formed.
a.

(i) Why is it necessary to lift the lid from time to time while heating?

[1]
b.

(ii) Why is it necessary to repeat the heating until two consecutive masses are the same?

[1]
c.

Show how the mass of magnesium oxide formed can be calculated from the readings obtained.

[1]
d.

The results of each student's experiment are given in the table below:

Mass of magnesium (g)Mass of magnesium oxide (g)
0.300.48
0.600.96
0.901.15
1.201.92
1.502.40
1.802.88

(i) Identify the anomalous result by stating the mass of magnesium for which it occurred.

[1]
e.

(ii) Use the consistent results from the table to calculate the mass of magnesium oxide formed when 1.35 g1.35\text{ g}1.35 g of magnesium is completely reacted.

[2]

Chemical formulae, equations and calculations Questions

  1. IGCSE
  2. /Chemistry
  3. /Chemical formulae, equations and calculations