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Author: Subject: Sodium Sulfate unusual solubility
bolbol
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[*] posted on 9-4-2019 at 07:46
Sodium Sulfate unusual solubility


I have been recently working on producing sodium sulfate crystals from saline lake waters. I was browsing on wikipedia when I found that the solubility increases tenfold at around 32 degrees celsius because thats the melting point of sodium sulfate decahydrate. I was blown away by this but couldnt find more information on this so I thought I'd ask here.

So if you have a salt solution what is different in the chemistry of bonding if the solutes are past their melting point?
Say we have a solution of a certain salt at 10 degrees Celsius. The salt by itself would be solid at room temperature. Say that same salt would be in liquid form by itself at a temperature of 40 degrees Celsius. If you bring the solution of that salt with water from 10 degrees C to 40 degrees C is there really any change? Because dissolved ions are dissolved ions in my mind and I can't see what would be different if they are past their melting point or not.. I just assume each ion is surrounded by a hydration sphere.

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Σldritch
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[*] posted on 9-4-2019 at 12:31


Perhaps the innermost solvation shell stays the same with most sodium ions. It is after all the one that should be bonded the tightest to the ions. In Sodium Sulfate's case it should be five per sodium ion, one less than what can be coordinated to it. In the solid decahydrate, it could be that the last two electrons in the sodium ion's shell is filled by the sulfate ion.

Also note that the rapid solubility increase is also due to the release of water from the hydrate forming a lower melting point mixture of water, decahydrate and lower hydrates.
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bolbol
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[*] posted on 10-4-2019 at 15:02


Quote: Originally posted by Σldritch  
Perhaps the innermost solvation shell stays the same with most sodium ions. It is after all the one that should be bonded the tightest to the ions. In Sodium Sulfate's case it should be five per sodium ion, one less than what can be coordinated to it. In the solid decahydrate, it could be that the last two electrons in the sodium ion's shell is filled by the sulfate ion.

Also note that the rapid solubility increase is also due to the release of water from the hydrate forming a lower melting point mixture of water, decahydrate and lower hydrates.


Excuse my ignorance but I do not understand the part about the release of water. When I think of a hydrate mineral, I can only imagine it in its solid form. When its dissolved I imagine it as a mixture of Na+, NaSO4-, Na2SO4, and SO4 2- ions moving around in the solution of water. How can the dissolved species be hydrated in the first place to be able to then release the water? How can the solution have a dissolved hydrate mineral?
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CharlieA
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[*] posted on 10-4-2019 at 15:58


Maybe this will help.

https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Coordination_Chemistry/Structure_and_Nomenclatu re_of_Coordination_Compounds/Ligands

Also, I don't know of any evidence for the species NaSO4-; do you have a reference to this?
Thanks, Charlie

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[*] posted on 10-4-2019 at 18:50


Quote: Originally posted by CharlieA  
Maybe this will help.

https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Coordination_Chemistry/Structure_and_Nomenclatu re_of_Coordination_Compounds/Ligands
Quote:
Sorry, the page at https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Coordination_Chemistry/Structure_and_Nomenclatu _re_of_Coordination_Compounds/Ligands could not be found.




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Molecular mass and elemental composition calculator: https://www.webqc.org/mmcalc.php
Solubility table: https://en.wikipedia.org/wiki/Solubility_table
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DraconicAcid
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[*] posted on 10-4-2019 at 19:24


Quote: Originally posted by fusso  
Quote: Originally posted by CharlieA  
Maybe this will help.

https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Coordination_Chemistry/Structure_and_Nomenclatu re_of_Coordination_Compounds/Ligands
Quote:
Sorry, the page at https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Coordination_Chemistry/Structure_and_Nomenclatu _re_of_Coordination_Compounds/Ligands could not be found.

Take out the extra bit in the middle of the word "Nomenclature"




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bolbol
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[*] posted on 11-4-2019 at 14:02


Okay so, at the temperature around 30 C, the dissolved species with 10 water molecules as ligands dehydrate. Meaning they are more stable with less ligands of water molecules around them?

Also, I don't have a reference for speciation of sodium sulfate in water but I am assuming all of those are present at some concentration. The dominant ones being Na+ and SO42-
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