Cement mixed with water undergoes an exothermic reaction. The heat evolved is called:
A. Heat of combustion
B. Heat of solution
C. Heat of fusion
D. Heat of hydration
Answer: Option D
Solution (By JKExamLibrary)
When cement hydrates, it releases heat known as heat of hydration. This exothermic process can cause thermal cracking in massive concrete structures if not controlled. The main compounds C₃S and C₃A have high heat of hydration. For dams, low-heat cement with lower C₃A content is used. Heat of solution is for dissolving, combustion for burning, fusion for melting.
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.
Explanation:
Nickel (finely divided) is used as a catalyst in the hydrogenation of unsaturated vegetable oils to saturated fats (vanaspati ghee). The reaction adds H₂ across double bonds. Platinum and palladium are also hydrogenation catalysts but nickel is cheaper and industrially preferred. Fe is used in Haber process for ammonia synthesis, V₂O₅ in contact process for H₂SO₄. Catalysts provide an alternative pathway with lower activation energy.
Explanation:
The amount of dissolved oxygen is crucial for aquatic life. The Biological Oxygen Demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material. High BOD indicates high organic pollution and low dissolved oxygen levels.
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