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Author: Subject: Why some salts form hydrates but others don't? Are there any ways to predict?
fusso
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[*] posted on 21-3-2019 at 10:07
Why some salts form hydrates but others don't? Are there any ways to predict?


In solid form, some soluble salts form hydrates (eg CuSO4) but others don't (eg NaCl), and even some organics and insoluble inorganics does too (eg oxalic acid, Ni4CO3(OH)6(H2O)4). Why is this? Are there any ways to predict whether a salt forms hydrate or not?

[Edited on 190322 by fusso]




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Neme
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[*] posted on 23-3-2019 at 13:15


If you want very rough prediction, for transition metal salts you can use 18 electron rule.
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DraconicAcid
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[*] posted on 23-3-2019 at 14:03


Quote: Originally posted by Neme  
If you want very rough prediction, for transition metal salts you can use 18 electron rule.


The 18 electron rule is followed for organometallic compounds, but not generally coordination compounds.




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fusso
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[*] posted on 24-3-2019 at 12:51


But AgNO3 doesn't form hydrates as well...



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brubei
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[*] posted on 24-3-2019 at 15:24


Polar bonds of water trend to bond with other polar compounds, such salts.
Adequate geometry for efficient pairing is also essential to give a good crystal


Il you take a look to a CuSO4.(H2O) crystal you can't miss de d orbitals of Cu and H
[img]https://en.wikipedia.org/wiki/Copper(II)_sulfate#/media/File:CuSO45aq.jpg[/img]

Sodium in NaCl don't have such empty orbitals so hydrating its crysta lead t it disorganization and melting.


[Edited on 24-3-2019 by brubei]




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