Hydrogen peroxide (H₂O₂) decomposes rapidly in the presence of a suitable catalyst, and releases oxygen (O₂) gas - Leaving Cert Chemistry - Question 3 - 2016

The balanced equation for the decomposition of hydrogen peroxide is:

$2H₂O₂ → 2H₂O + O₂$

To plot the graph:

1. Label the y-axis as 'Volume of Oxygen (cm³)' and the x-axis as 'Time (minutes)'.
2. Use the provided data points to plot each interval accurately:
   • (0, 50), (2, 69), (4, 75), (8, 78), (10, 79), (12, 79)
3. Join the points smoothly to indicate the curve of reaction over time.

From the graph, the volume of oxygen produced during the first three minutes can be calculated as the difference between the volume at 2 minutes (69 cm³) and the volume at 0 minutes (50 cm³), which gives:

$69 ext{ cm³} - 50 ext{ cm³} = 19 ext{ cm³}$

The reaction slows down as time progresses because the concentration of the hydrogen peroxide decreases as it is being consumed. As the reaction progresses, there are fewer reactant molecules available to collide and react, leading to a decrease in the rate of oxygen production.

If the reaction were repeated with the conical flask cooled in ice-water, the graph would show a steeper initial rise because the cooler temperature would typically increase the rate of reaction due to decreased activation energy. The curve should approach the same volume of oxygen at saturation, but the rate of production in the early minutes would be greater.