In the electrolytic extraction of calcium from calcium chloride, the cathode is

Analysis

The question asks for the material used as the cathode during the electrolytic extraction of calcium from molten calcium chloride ($CaCl_2$).

Concept Explanation

In the industrial extraction of calcium by electrolysis, the electrolyte is molten calcium chloride. Because calcium is a highly reactive metal, it cannot be extracted from aqueous solutions (as hydrogen would be discharged instead).

During this process:

• The Anode: Usually made of graphite, where chloride ions are oxidized to chlorine gas.
• The Cathode: This is where calcium ions ($Ca^{2+}$) are reduced to metallic calcium ($Ca$).

In this specific industrial setup, the cathode is typically made of iron. The molten calcium collects on the iron cathode, which is often kept at a temperature just above the melting point of calcium so that the metal can be tapped off.

Step-by-Step Solution

1. Identify the process: Electrolytic extraction of calcium from molten $CaCl_2$.
2. Understand the components: The cell requires an inert or suitable metal for the electrodes.
3. Evaluate the cathode: In the standard industrial method (the Downs cell or similar electrolytic processes for alkaline earth metals), an iron rod or iron lining is used as the cathode because it is durable and does not readily react with the molten calcium at the operating temperatures.
4. Compare with options: • Zinc (A) is not used as a cathode here. • Graphite (B) is typically used as the anode. • Platinum (C) is an inert electrode but is too expensive for large-scale industrial extraction. • Iron (D) is the standard material used for the cathode in this process.

Conclusion

Exam Tip

When studying electrolysis, always remember the "Anode-Oxidation, Cathode-Reduction" (A-O-C-R) rule. Also, for industrial extractions, remember that graphite is almost always the anode (because it can withstand the chlorine gas produced), while iron or steel is commonly used as the cathode for reactive metals.