Question

Calcium is obtained by the

• A. roasting of limestone
• B. electrolysis of solution of calcium chloride in $H_2O$
• C. electrolysis of molten anhydrous calcium chloride
• D. reduction of calcium chloride with carbon

Answer 1

The Correct Option is C

The question asks about the method used to obtain calcium. Let's analyze each option to determine the correct method:

1. Roasting of limestone: Roasting limestone, which is primarily calcium carbonate (CaCO_3), results in calcium oxide (CaO), not pure calcium. This method is used to produce lime, but not metallic calcium.
2. Electrolysis of a solution of calcium chloride in H_2O: Electrolyzing a solution would likely produce hydroxides due to the presence of water. It is not a standard method to obtain pure metallic calcium.
3. Electrolysis of molten anhydrous calcium chloride: This is the correct method. By electrolyzing molten anhydrous calcium chloride (CaCl_2), calcium metal and chlorine gas are produced. The reaction is as follows:
   \text{CaCl}_2 \rightarrow \text{Ca}^{2+} + 2\text{Cl}^{-}
   \text{Cathode}: \text{Ca}^{2+} + 2\text{e}^{-} \rightarrow \text{Ca} (Calcium metal is deposited at the cathode)
   \text{Anode}: 2\text{Cl}^{-} \rightarrow \text{Cl}_2 + 2\text{e}^{-} (Chlorine gas is liberated at the anode)
4. Reduction of calcium chloride with carbon: This method is not feasible for obtaining pure calcium. Reduction by carbon is more applicable for producing metal oxides rather than active metals like calcium.

Hence, the correct answer is the electrolysis of molten anhydrous calcium chloride. This method allows the extraction of free calcium metal efficiently.