Which catalyst is used in the decomposition of KClO₃ to prepare oxygen in the laboratory?
A. V₂O₅
B. Pt
C. MnO₂
D. Fe₂O₃
Answer: Option C
Solution (By JKExamLibrary)
Manganese dioxide (MnO₂) catalyzes the thermal decomposition of potassium chlorate: 2KClO₃ (heat, MnO₂) → 2KCl + 3O₂. Without MnO₂, decomposition requires higher temperature. MnO₂ is not consumed. Other catalysts can be used, but MnO₂ is standard in school labs. V₂O₅ is for SO₂ oxidation, Pt for various, Fe₂O₃ not typical. This is a simple preparation of oxygen.
Explanation:
A negative catalyst (inhibitor) decreases the rate of a reaction by increasing activation energy or destroying active intermediates. Example: phosphoric acid inhibits H₂O₂ decomposition. Positive catalysts speed up, enzymes are biocatalysts, autocatalysts are products that catalyze their own formation.
Explanation:
Gypsum (CaSO₄·2H₂O) is added to clinker to control the rapid reaction of tricalcium aluminate with water, which would otherwise cause flash (quick) setting. Gypsum slows down the hydration of C₃A, thus increasing the setting time and allowing workability. Without gypsum, cement would set almost immediately upon mixing with water, making placement impossible.
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