Which of the following methods is used to obtain pure copper from impure copper?
A. Calcination
B. Roasting
C. Smelting
D. Electrolytic refining
Answer: Option D
Solution (By JKExamLibrary)
In electrolytic refining, impure copper is the anode, pure copper is the cathode, and CuSO₄ acidified with H₂SO₄ is the electrolyte. Copper dissolves from anode and pure copper deposits on cathode. Smelting is reduction with coke.
Explanation:
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:
On boiling, soluble calcium bicarbonate decomposes: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. The precipitate is calcium carbonate (limestone/chalk). Magnesium bicarbonate similarly forms MgCO₃ or Mg(OH)₂. This removes Ca²⁺ and Mg²⁺ ions, softening the water. Permanent hardness (CaSO₄, CaCl₂) doesn't precipitate on boiling and needs chemical treatment.
No comments yet. Be the first to start the discussion!