Chemistry 2000 JAMB Past Questions - Question 4: 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?

Correct Answer

C

Explanation

To determine which reactant was in excess, we can start by calculating the amount of oxygen present in the air and then compare it to the amount required for the complete combustion of the carbon (II) oxide.

First, let's find the amount of oxygen in 150 cm³ of air:
150 cm³ ×  20% = 150 cm  × 0.20³ = 30 cm³ of oxygen

The balanced chemical equation for the combustion of carbon (II) oxide is:
2CO + O2→ 2CO2

From the equation, we can see that 1 mole of CO reacts with 0.5 moles of O2 Therefore, the amount of oxygen required for the complete combustion of 50 cm³ of CO is:
50 cm³ × (0.5/2) = 12.5 cm of oxygen

Since the amount of oxygen required for the complete combustion of 50 cm³ of CO is 12.5 cm³ , and the amount of oxygen present in the air is 30 cm³ , it's clear that the oxygen in the air is in excess.