In the extraction of zinc from zinc blende (ZnS), the first step is:
A. Smelting with coke
B. Roasting in air
C. Electrolysis
D. Leaching with NaOH
Answer: Option B
Solution (By JKSSB Mock Tests)
Zinc blende (ZnS) is first concentrated by froth flotation, then roasted in excess air to convert it to ZnO: 2ZnS + 3O₂ → 2ZnO + 2SO₂. ZnO is then reduced with coke at high temperature (smelting) or dissolved in H₂SO₄ and electrolyzed. Roasting is typical for sulfide ores to remove sulfur as SO₂.
Explanation:
Temporary hardness is due to dissolved bicarbonates of Ca and Mg. These can be removed by boiling, which precipitates carbonates. Calcium sulfate and chloride cause permanent hardness. Sodium chloride does not cause hardness. Boiling: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Bicarbonates are formed when water containing CO₂ passes over limestone.
Explanation:
Methane is CH₄, the simplest alkane with one carbon atom bonded to four hydrogen atoms. The series general formula is CₙH₂ₙ₊₂. For n=1, H=4. CH, CH₂, CH₃ are not stable neutral molecules; they are fragments (methyl radical etc.). Methane is a major component of natural gas and biogas.
Explanation:
Hydrogen has about 150 kJ/g (highest). Petrol ~47 kJ/g, coal ~25-35 kJ/g, cow dung cake ~8 kJ/g. Hydrogen produces only water on combustion and is a clean fuel.
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