Video Transcript
Copper(II) oxide and chromium(III)
oxide can both be used as catalysts for the decomposition of hydrogen peroxide, as
shown: two H2O2 aqueous reacts to form two H2O liquid plus O2 gas. In experiment A, copper(II) oxide
is used, and in experiment B, chromium(III) oxide is used. The results are shown on the graph
below. Which of the catalysts is the best
and why? (A) Chromium(III) oxide is the
better catalyst; the less steep slope indicates a faster rate of reaction. (B) Chromium(III) oxide is the
better catalyst; the steeper slope indicates a faster rate of reaction. (C) Copper(II) oxide is the better
catalyst; the less steep slope indicates a faster rate of reaction. Or (D) copper(II) oxide is the
better catalyst; the steeper slope indicates a faster rate of reaction.
In this question, we’re looking to
identify the most effective catalyst. We also need to explain our
choice.
The figure shows the decomposition
of hydrogen peroxide in the presence of two different substances. The red and blue lines represent
copper(II) oxide and chromium(III) oxide, respectively. You’ll notice that both lines have
a similar shape, but one has a steeper slope than the other. The graphs have the mass of the
reaction vessel on the 𝑦-axis and time on the 𝑥-axis.
We can infer that a steeper line
represents a more rapid decomposition of hydrogen peroxide reactant. This is because the loss of mass is
what indicates hydrogen peroxide decomposition, where the product, oxygen, is lost
as a gas into the atmosphere, decreasing the mass of the vessel. In the chart shown, the blue line
has a steeper slope and therefore represents hydrogen peroxide turning into water
and oxygen more rapidly.
And with this information, we can
answer the question. Which catalyst, copper(II) oxide or
chromium(III) oxide, is the best catalyst for the decomposition of hydrogen
peroxide? And because the steeper slope
correlates to a better catalyst, we can choose answer choice (B) as the correct
answer. Chromium(III) oxide is the better
catalyst; the steeper slope indicates a faster rate of reaction.
