Molten Salt: Disassociation or Vibration?

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Discussion Overview

The discussion revolves around the molecular nature of molten salts, specifically calcium chloride (CaCl2) at high temperatures, and whether the ions are disassociated like in a solution or remain paired due to molecular vibrations. Participants also explore the potential for chlorine gas production from molten salt and the implications for electrochemical processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions whether molten CaCl2 at 800°C results in disassociated ions or if the ions remain paired due to high molecular vibration.
  • Another participant asserts that molten salt solutions conduct electricity, indicating the presence of ions, and suggests that chlorine gas could be produced if the temperature is sufficiently high.
  • A participant emphasizes that molten anhydrous salt may not qualify as a solution and questions the dissociative rate of ions versus the presence of free-flowing CaCl2 molecules.
  • There is mention of the Downs Cell process, which utilizes molten sodium chloride to produce metallic sodium and releases chlorine gas, suggesting a parallel to the discussion on CaCl2.
  • One participant seeks to quantify the percentage of ions in the molten salt mix and discusses the implications for purifying the salt.
  • Another participant notes that at 800°C, CaCl2 likely does not dissociate into Cl2 and introduces the concept of "activity of molten salt solutions."

Areas of Agreement / Disagreement

Participants express differing views on whether molten CaCl2 behaves as a solution with disassociated ions or remains as paired molecules. There is no consensus on the molecular nature of molten salts or the conditions under which chlorine gas might be produced.

Contextual Notes

Participants reference the need for specific temperature thresholds for reactions and the role of impurities in the conductivity of molten salts. The discussion includes unresolved questions about the dissociative behavior of ions and the electrochemical processes involved.

Andronicus1717
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Generally, when you melt a salt (CaCl2 @800deg C specifically) are the ions disassociated as in a solution or is molecular vibration simply great enough to not allow the formation of intermolecular bonds and the atoms are floating around still paired? This is probably a dumb question and my overwhelming instinct is the latter, anyone care to confirm?

Also, will there be the potential for Chlorine gas to be produced to be exhumed from the molten salt, again my instinct is no, but at such high temperatures there might be the potential for the ionic bonds to be displaced in a collision and form Cl2? Enthalpy of formation of CaCl2 is -795.4 kJ/mol for a solid, I'll see if I can find it for a liquid and run the numbers for the reaction CaCl2(l) -> Ca(?) + Cl2(g). Would this reaction be accelerated if there was a galvanic cell taking place in the mix?
 
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Most molten salt solutions conduct electricity so they exist as ions. As for producing chlorine, it is possible if the temperature is high enough.

CaCl2 + heat <--------> Ca + Cl2(g)

As shown the reaction is reversible. Just add heat to force the reaction to the right. How much heat (temperature) is the question. I do not know the decomposition temperature of CaCl2 but it can be found easily, I'm sure.
 
This is simply molten anhydrous molten salt, so I don't think that qualifies it as a solution. It is a solvent to some solutes like CaO but that is on a minimal scale so maybe like water it is those impurities which make it an electrolyte, but as the process that I'm designing is supposed to purify the salt. Would it still be an electrolyte?

I know in the Plutonium electro-refining process they use a separate PuF4 electrolyte in the molten salt medium.

So I ask again what is the molecular nature of molten salt? Is there a dissociative rate of the ions or do they exist as free flowing CaCl2 molecules?Edit*

Molten salts conduct electricity the same way they do when they are dissolved in water; some of the salt molecules are dissociated into ions, which allows the ions to conduct electricity. The "Downs Cell" capitalizes on this conduction of electricity to produce virtually all of the metallic sodium required by industry. Electricity is run through molten sodium chloride (with a little calcium chloride salt added to lower the melting point of the sodium chloride). At one terminal chlorine gas is released (the anode) and at the other (the cathode) liquid sodium.
http://72.14.253.104/search?q=cache...Sal.html+molten+salt&hl=en&ct=clnk&cd=1&gl=us

Found this google cache with some good information and references. Now I need to try and qualify the percentage of ions floating around in the mix, any ideas?
 
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Andronicus1717 said:
This is simply molten anhydrous molten salt, so I don't think that qualifies it as a solution. It is a solvent to some solutes like CaO but that is on a minimal scale so maybe like water it is those impurities which make it an electrolyte, but as the process that I'm designing is supposed to purify the salt. Would it still be an electrolyte?

I know in the Plutonium electro-refining process they use a separate PuF4 electrolyte in the molten salt medium.

So I ask again what is the molecular nature of molten salt? Is there a dissociative rate of the ions or do they exist as free flowing CaCl2 molecules?


Edit*

Molten salts conduct electricity the same way they do when they are dissolved in water; some of the salt molecules are dissociated into ions, which allows the ions to conduct electricity. The "Downs Cell" capitalizes on this conduction of electricity to produce virtually all of the metallic sodium required by industry. Electricity is run through molten sodium chloride (with a little calcium chloride salt added to lower the melting point of the sodium chloride). At one terminal chlorine gas is released (the anode) and at the other (the cathode) liquid sodium.
http://72.14.253.104/search?q=cache...Sal.html+molten+salt&hl=en&ct=clnk&cd=1&gl=us

Found this google cache with some good information and references. Now I need to try and qualify the percentage of ions floating around in the mix, any ideas?

If it is your intention to purify this salt by melting and applying some process to the molten salt, the molten salt does behave as a solution. It is a solution for the impurities...

At 800 C, CaCl2 probably doesn't dissociate into Cl2. The term you are looking for is "activity of molten salt solutions".

See here:

http://adsabs.harvard.edu/abs/1973iams.rept...3S
 
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