Which of the following is an example of a negative catalyst?
A. Alcohol in chloroform storage to prevent phosgene formation
B. Pt in SO₂ oxidation
C. Fe in Haber process
D. MnO₂ in H₂O₂ decomposition
Answer: Option A
Solution (By JKExamLibrary)
A small amount of ethanol (alcohol) is added to chloroform to inhibit its oxidation by air to toxic phosgene (COCl₂) and HCl. Ethanol acts as a negative catalyst (stabilizer) by consuming any formed phosgene. MnO₂, Pt, Fe are positive catalysts. Negative catalysts are also called inhibitors, used to prevent undesirable reactions.
Explanation:
Joseph Proust proposed the law of definite proportions (constant composition) – a given compound always contains the same elements in the same proportion by mass. Dalton's theory explained it. Lavoisier gave law of conservation of mass. Rutherford discovered nucleus.
Explanation:
Petroleum is a mixture of hydrocarbons with close boiling points. Fractional distillation uses a fractionating column to separate them efficiently based on repeated condensation–vaporization cycles. Simple distillation cannot separate liquids with boiling point difference less than 25 K effectively. Filtration and sublimation are not applicable.
Explanation:
Bauxite contains SiO₂ (silica) as impurity. In the Bayer's process, powdered bauxite is treated with hot concentrated NaOH solution. Alumina dissolves forming sodium aluminate (NaAlO₂), while silica does not dissolve and is filtered off. Alternatively, silica can be removed by adding lime during refining. The purified alumina is then electrolyzed in cryolite. NaOH selectively dissolves Al₂O₃ due to its amphoteric nature.
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