Understanding Oxygen Production from Potassium Chlorate

The question asks us to evaluate two statements about the production of oxygen gas from potassium chlorate and the role of manganese dioxide.

Analyzing Statement I: Rate of Oxygen Production

Statement I says that oxygen gas is produced faster by heating a mixture of Potassium Chlorate ($\text{KClO}_3$) and Manganese dioxide ($\text{MnO}_2$) than by heating Potassium chlorate alone.

Potassium chlorate decomposes upon heating to produce potassium chloride ($\text{KCl}$) and oxygen gas ($\text{O}_2$). The chemical equation for this reaction is:

$\text{2KClO}_3\text{(s)} \xrightarrow{\text{heat}} \text{2KCl(s)} + \text{3O}_2\text{(g)}$

This decomposition reaction is relatively slow when potassium chlorate is heated by itself.

However, when a small amount of manganese dioxide ($\text{MnO}_2$) is added to the potassium chlorate, the decomposition proceeds much faster and at a lower temperature. Manganese dioxide is not consumed in the reaction; it only helps to speed it up. A substance that increases the rate of a chemical reaction without being consumed is called a positive catalyst.

Therefore, adding manganese dioxide to potassium chlorate indeed makes the production of oxygen gas happen at a faster rate compared to heating potassium chlorate alone. Statement I is true.

Analyzing Statement II: Manganese Dioxide as a Negative Catalyst

Statement II says that Manganese dioxide acts as a negative catalyst.

A catalyst is a substance that alters the rate of a chemical reaction. Catalysts can be classified as positive or negative:

• Positive catalyst: Increases the rate of a chemical reaction.
• Negative catalyst (or inhibitor): Decreases the rate of a chemical reaction.

As discussed when analyzing Statement I, manganese dioxide speeds up the decomposition of potassium chlorate. This means manganese dioxide increases the rate of oxygen production.

Since manganese dioxide increases the reaction rate, it acts as a positive catalyst, not a negative catalyst. Statement II is false.

Conclusion based on Statement Analysis

Based on our analysis:

• Statement I: Oxygen production is faster with $\text{MnO}_2$. This is true.
• Statement II: Manganese dioxide acts as a negative catalyst. This is false (it's a positive catalyst).

We are looking for the option that states Statement I is true and Statement II is false.

Comparing this with the given options:

• Option 1: Both true and Statement II is the correct explanation of statement I (Incorrect, Statement II is false).
• Option 2: Both true but Statement II is not the correct explanation of Statement I (Incorrect, Statement II is false).
• Option 3: Statement I is true but Statement II is false (Correct, matches our analysis).
• Option 4: Statement I is false but Statement II is true (Incorrect, Statement I is true and Statement II is false).

Therefore, the correct option is that Statement I is true but Statement II is false.

Revision Table: Potassium Chlorate and Manganese Dioxide

Additional Information: Catalysis in Oxygen Production

The decomposition of potassium chlorate is a common laboratory method for preparing oxygen gas. The reaction requires significant heating to occur at a reasonable rate when only $\text{KClO}_3$ is used. However, the presence of manganese dioxide lowers the activation energy required for the reaction, allowing it to proceed much faster at a lower temperature.

This process is a classic example of heterogeneous catalysis, where the catalyst ($\text{MnO}_2$, a solid) is in a different phase from the reactant ($\text{KClO}_3$, a solid, decomposing into $\text{KCl}$ solid and $\text{O}_2$ gas). While $\text{MnO}_2$ isn't chemically changed overall, its surface plays a crucial role in facilitating the decomposition.

It is important to distinguish between positive and negative catalysts. Positive catalysts are used to speed up desired reactions, making them more efficient. Negative catalysts or inhibitors are used to slow down or prevent unwanted reactions, such as the spoilage of food or corrosion.

In summary, manganese dioxide's effect on potassium chlorate decomposition is to increase the reaction rate, confirming its role as a positive catalyst for oxygen production.