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Difficulty: EasyAlkali Metals: Sodium Extraction, Properties, and Compounds

In the industrial extraction of sodium metal using the Downs cell, calcium chloride (CaCl2\text{CaCl}_2) is added to molten sodium chloride (NaCl\text{NaCl}) primarily to:

  1. lower the melting point of the sodium chloride electrolyteAnswer
  2. B
    act as a reducing agent for sodium ions
  3. C
    prevent chlorine gas from discharging at the graphite anode
  4. D
    increase the solubility of sodium metal in the molten mixture

Answer

Calcium chloride is added to lower the melting point of the sodium chloride electrolyte.
Pure sodium chloride melts at 801∘C801^\circ\text{C}. Adding calcium chloride lowers the melting point of the mixture to about 600∘C600^\circ\text{C}, which conserves energy and minimizes evaporation of the liberated sodium metal during electrolysis in the Downs cell.

Step-by-Step Solution

1
Identify the physical properties of pure sodium chloride
Pure NaCl\text{NaCl} has a high melting point of approximately 801∘C801^\circ\text{C}.
Maintaining such a high temperature industrially requires significant thermal energy.
2
Determine the effect of adding calcium chloride (CaCl2\text{CaCl}_2)
Mixing CaCl2\text{CaCl}_2 with NaCl\text{NaCl} forms an electrolytic mixture with a reduced melting point of about 600∘C600^\circ\text{C}.
Lowering the melting point makes the process economically viable and reduces heat loss and electrode wear.

Key Concept

Function of flux/admixture in the Downs process for sodium extraction
Estimated Time:45s
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Topics

Alkali Metals: Sodium Extraction, Properties, and Compounds

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