CAIE A Level Chemistry 9701 · Atoms, molecules and stoichiometry

Atoms, molecules and stoichiometry: compare question

Compare5 marksStandard

Nitrogen reacts with oxygen to form nitrogen monoxide.

\ce{N2(g) + O2(g) -> 2NO(g)}

In an experiment, 40 cm³ of nitrogen is mixed with 60 cm³ of oxygen and the mixture is sparked so that the reaction goes to completion. All volumes are measured at room temperature and pressure.

(a) Compare the volumes of the two gases used in the experiment with the volume ratio required by the equation.

(b) State which reactant is in excess.

(c) State how the volume of nitrogen monoxide formed compares with the volume of the reactant that is used up completely, and state what this shows about the stoichiometric relationship between gas volumes in this reaction.

How this question is marked

5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.

Compare means: Give similarities or differences between two things, and say which side each point belongs to. Write each point as a pair, for example: A is X, whereas B is Y. Two separate descriptions rarely earn the marks.

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