A student wants to prepare oxygen gas in the laboratory. Which combination of reagents and collection method is appropriate?
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Correct answer
D. Potassium chlorate and manganese dioxide, collected by downward displacement of water
Principle or equation
Oxygen is commonly prepared by decomposition of hydrogen peroxide with manganese dioxide as a catalyst, or by heating potassium chlorate with manganese dioxide as a catalyst. Oxygen is slightly denser than air and can be collected by upward displacement of air or over water. The correct option must produce oxygen and use an appropriate collection method.
Why this answer is correct
Potassium chlorate (KClO3) decomposes when heated with MnO2 as a catalyst to produce oxygen gas. Oxygen is only slightly soluble in water and can be collected by downward displacement of water (i.e., over water). The other options produce hydrogen or carbon dioxide, not oxygen.
Example
2KClO3(s) → 2KCl(s) + 3O2(g) (with MnO2 catalyst and heat).
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