In the extraction of iron in a blast furnace, limestone is added to:
A. Lower the melting point of iron
B. Reduce iron oxide
C. Remove silica as slag
D. Increase carbon content
Answer: Option C
Solution (By JKSSB Mock Tests)
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:
Normal rainwater is slightly acidic with a pH of about 5.6. This is due to the natural dissolution of carbon dioxide from the air into the rain droplets, forming weak carbonic acid (CO₂ + H₂O ⇌ H₂CO₃). Acid rain has a pH lower than 5.6 due to pollutants.
Explanation:
Lead-acid batteries (used in automobiles) contain dilute sulfuric acid (H₂SO₄) with specific gravity around 1.25-1.30 when fully charged. It acts as electrolyte and participates in the electrode reactions. Nitric acid is a strong oxidizing agent, HCl is not used because it would produce chlorine, phosphoric acid is in some fuel cells but not lead-acid batteries.
Explanation:
Mendeleev named the missing element eka-aluminium. When gallium was discovered (1875), its properties (density, oxide formula) closely matched Mendeleev's predictions, validating his table. Germanium was eka-silicon; scandium was eka-boron. These predictions were a triumph of the periodic law. Gallium has a low melting point (~30°C) and is used in semiconductors. Mendeleev corrected atomic masses based on group properties.
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