1(a) What is the meaning of empirical formula?
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[1 mark]
(ii) A carbon compound X has an empirical formula of CH2 and a molar mass of 70 g mol-1. Determine the molecular formula of compound X.
[3 marks]
(b) A group of students carried out an experiment to determine the empirical formula of magnesium oxide.
(i) Draw the apparatus set up for the experiment.
[2 marks]
Mass of crucible + lid = 24.88 g
Mass of crucible + lid + magnesium ribbon = 25.12 g
Mass of crucible + lid + magnesium oxide = 25.28 g
Diagram 1
(ii) Based on Diagram 1, complete Table 1 and determine the empirical formula of magnesium oxide.
Element | Mg | O |
Mass (g) | ||
Number of moles | ||
Simplest ratio of moles | ||
Empirical Formula | ||
Table 1
[6 marks]
(iii) Write the chemical equation for the reaction in the experiment.
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[1 mark]
(c) Why the process of heating, cooling and weighing are repeated until constant mass is obtained?
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[1 mark]
(d) Why this experiment is not suitable to be used to determine the empirical formula of copper(II) oxide?
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[1 mark]
2. A group of students carried out an experiment to determine the empirical formula
of magnesium oxide.
Result :
Mass of crucible + lid = 24.0 g
Mass of crucible + lid + magnesium ribbon = 26.4 g
Mass of crucible + lid + magnesium oxide = 28.0 g
(a) What is meant by empirical formula?
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........................…………………………………………………………………………………………………. [1 mark]
(b) Based on the above results,
Calculate the empirical formula of magnesium oxide.
[3 markah]
(c) write the chemical equation for the reaction in the experiment.
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[1 mark]
(d) Why was the crucible lid opened once in a while during the experiment?
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[ 1 mark]
(e) Metal X is placed below hydrogen in the reactivity series. You are required to carry out an experiment to determine the empirical formula of the oxide of metal X. The apparatus provided are combustion tube, glass tube, cork, Bunsen burner and porcelain dish.
(i) draw a labelled diagram of the set-up of the apparatus for the experiment.
[2 marks]
(ii) Describe the steps that should be taken to ensure that all the air in the combustion tube has
been expelled.
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[3 marks]
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