In the extraction of iron in a blast furnace, limestone is added to:
A. Reduce iron oxide
B. Increase carbon content
C. Lower the melting point of iron
D. Remove silica as slag
Answer: Option D
Solution (By JKExamLibrary)
Limestone (CaCO₃) decomposes to CaO, which is a basic flux. It reacts with the acidic impurity silica (SiO₂) to form calcium silicate (CaSiO₃), a fusible slag: CaO + SiO₂ → CaSiO₃. Slag floats on molten iron and is tapped separately. Reduction is done by CO/coke. Flux makes gangue removal easier. Slag is used in cement, road building.
Explanation:
Ionic (electrovalent) bond is formed by complete transfer of one or more valence electrons from a metal (low ionization energy) to a non-metal (high electron affinity), resulting in oppositely charged ions held by electrostatic forces. Example: Na → Na⁺ + e⁻; Cl + e⁻ → Cl⁻; Na⁺Cl⁻. Covalent bond involves sharing. Coordinate bond involves donation.
Explanation:
Calorific value is the amount of heat energy produced by complete combustion of unit mass of a fuel. SI unit is J/kg, often expressed as kJ/kg or MJ/kg. Previously, kcal/kg or cal/g was used. 1 cal = 4.184 J. Higher calorific value indicates better fuel. Example: hydrogen has very high calorific value ~150 MJ/kg. Exam note: Calorific value is measured by bomb calorimeter.
Explanation:
MnO₂ oxidizes HCl (Cl⁻ to Cl₂) while itself being reduced (Mn⁴⁺ to Mn²⁺). Oxidizing agent (oxidant) accepts electrons and gets reduced. Here, MnO₂ accepts electrons from Cl⁻. HCl is the reducing agent (reductant) as it loses electrons. This reaction was used by Scheele to discover chlorine. Exam tip: The substance reduced is the oxidizing agent; the substance oxidized is the reducing agent.
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