Electrolysis and Metal Extraction

Electrolysis is a process that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. In metallurgy, it's a crucial technique for extracting metals from their ores or compounds, especially when other methods like smelting are not suitable.

Extraction of Reactive Metals

Highly reactive metals, like Sodium (Na), Potassium (K), Magnesium (Mg), and Aluminum (Al), have a strong affinity for non-metals (like oxygen or chlorine). Their compounds are very stable, making it difficult to extract the pure metal using simple chemical reduction (like heating with carbon). For these metals, electrolysis of their molten compounds is the preferred industrial method. Melting is necessary because the molten state allows the ions to move freely and conduct electricity.

Analyzing the Options

Let's look at the extraction methods for the metals listed:

• Copper (Cu): While copper can be purified using electrolysis (electrorefining), its primary extraction from ores often involves smelting (heating with a reducing agent like carbon) and other processes. It's not typically extracted from a molten compound via electrolysis for initial production.
• Gold (Au): Gold is usually extracted using chemical methods like cyanide leaching, followed by precipitation or electrolysis of the resulting solution, not typically from a molten compound.
• Tin (Sn): Tin is primarily extracted by smelting its ore (cassiterite, $SnO_2$) with carbon in a furnace.
• Sodium (Na): Sodium is a highly reactive alkali metal. It is commercially extracted by the electrolysis of molten sodium chloride ($NaCl$) in a process known as the Downs Process. This method is specifically designed for the electrolysis of molten salts to obtain reactive metals.

The Downs Process for Sodium Extraction

In the Downs Process:

1. Molten sodium chloride ($NaCl$) is used as the electrolyte. Calcium chloride ($CaCl_2$) is often added to lower the melting point, reducing energy costs.
2. The electrolysis occurs in a specialized cell at temperatures around $600^\circ C$.
3. At the cathode (negative electrode), sodium ions ($Na^+$) gain electrons to form molten sodium metal: $ Na^+ + e^- \rightarrow Na_{(l)} $
4. At the anode (positive electrode), chloride ions ($Cl^-$) lose electrons to form chlorine gas ($Cl_2$): $ 2Cl^- \rightarrow Cl_2_{(g)} + 2e^- $

This method is widely used because it efficiently produces pure sodium metal.

Conclusion

Based on the analysis, Sodium (Na) is the metal among the given options that is widely extracted by the electrolysis of its molten compound (molten $NaCl$).