Here's why:

* Freezing point depression: The addition of a solute, like calcium chloride, to a solvent, like sodium, lowers the freezing point of the solvent. This is a colligative property, meaning it depends only on the concentration of the solute, not its identity.

* Why is this important? Lowering the freezing point of sodium is beneficial for various applications, particularly in the production of sodium metal.

* The process:

* Sodium is usually produced by the electrolysis of molten sodium chloride.

* Adding calcium chloride lowers the freezing point of the sodium chloride mixture, allowing the electrolysis to occur at a lower temperature.

* This makes the process more energy-efficient and cost-effective.

Key points:

* Melting point: The temperature at which a solid transitions to a liquid.

* Freezing point: The temperature at which a liquid transitions to a solid.

* Freezing point depression: The phenomenon where the freezing point of a solvent is lowered by the addition of a solute.

In summary, calcium chloride is added to sodium (specifically, sodium chloride) to lower its freezing point, making the electrolysis process more efficient.