50 cm³ of carbon (II) oxide was exploded with 150 cm³ of air containing 20% oxygen by volume. Which of the reactants was in excess?

A. Carbon (II) oxide
B. Carbon (IV) oxide
C. Oxygen
D. Nitrogen

Correct Answer:

Option C – Oxygen

Explanation

2CO + O2 → 2CO2
50cm³ → 25cm³
20% X 150 = 30cm³

30cm³ is the volume of oxygen available for the reactions. But only 25 cm³ is required; therefore O2 is in excess