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Question Video: Identifying the Correct Statement For the Decomposition of Hydrogen Peroxide Using a Manganese Dioxide Catalyst Chemistry • 7th Grade

Manganese dioxide is used as a catalyst in the decomposition of hydrogen peroxide to form water and oxygen. Which statement is untrue when using MnO₂ as a catalyst? [A] The oxygen will be formed more quickly. [B] More oxygen will be produced. [C] The mass of MnO₂ before and after the reaction will be the same. [D] An alternative reaction pathway is provided by the catalyst. [E] The catalyst remains unchanged at the end of the experiment.

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Video Transcript

Manganese dioxide is used as a catalyst in the decomposition of hydrogen peroxide to form water and oxygen. Which statement is untrue when using MnO2 as a catalyst? 2H2O2 aqueous produces 2H2O liquid plus O2 gas. (A) The oxygen will be formed more quickly. (B) More oxygen will be produced. (C) The mass of MnO2 before and after the reaction will be the same. (D) An alternative reaction pathway is provided by the catalyst. (E) The catalyst remains unchanged at the end of the experiment.

In this question, we’re being asked about how a catalyst, which is manganese dioxide, behaves in a decomposition reaction. In this decomposition reaction, a single reactant, the hydrogen peroxide, decomposes to form new products. The products are water and oxygen gas. This decomposition reaction is very slow under normal conditions at room temperature. We would not observe many bubbles of oxygen gas coming from the hydrogen peroxide solution at all. This situation would change rapidly if a small amount of the solid catalyst, manganese dioxide, were added to the hydrogen peroxide solution.

Rapid fizzing or effervescence would be observed as soon as the black powder is added to the hydrogen peroxide. The manganese dioxide catalyst will increase the rate of decomposition of the hydrogen peroxide. More oxygen gas, seen as bubbles, will be produced per unit of time as the reaction rate has been increased. Oxygen gas will certainly be produced more rapidly. This statement is true, so it’s not the correct answer. Remember, in this question, we’re looking for an untrue statement.

Notice that the oxygen gas, which is one of the products, originates from the hydrogen peroxide molecules. According to the balanced equation, two molecules of hydrogen peroxide are required to produce one molecule of oxygen gas. If we have a fixed amount of hydrogen peroxide molecules at the start of the reaction, we can only produce a fixed amount of oxygen molecules during the decomposition reaction. Adding the manganese dioxide catalyst does not change the amount of oxygen gas produced. It simply increases the rate of reaction.

The same amount of oxygen gas is produced in much less time. The manganese dioxide does not appear in the overall reaction equation. The amount of oxygen gas obtained will be the same with or without the catalyst present. This means that the statement that more oxygen gas is produced is untrue. Therefore, it’s likely to be the correct answer.

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