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Looking at most of the sulphate salts (there are so many but just to name some Epsom salt, blue vitirol, gypsum...) they have some amount of water crystallized within them (Epsom salt is $\ce{MgSO4.7H2O, CuSO4.5H2O}$ is blue vitirol and so on) so why is it like that? Is there any reason why water is crystallized in almost all metal sulphates?

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    $\begingroup$ Now that you've changed the meaning of the question entirely, let's look into it. BaSO4 seems to crystallize without water; so does K2SO4. Still sure about "most"? Well, maybe the majority of all salts, not just sulphates, crystallize with water in them. $\endgroup$ Nov 17, 2023 at 13:10
  • $\begingroup$ @IvanNeretin oh okay but I still think (not believe) that sulphates are the most to somehow grab water in them.....you would be right though and it just may not be sulphates (like the next best bet would be chlorides)........and yea i amn't sure so waiting for more responses :) $\endgroup$ Nov 17, 2023 at 14:36
  • $\begingroup$ @IvanNeretin basically I am finding for some chemical bonding-ish solution if it even exists :') $\endgroup$ Nov 17, 2023 at 14:38
  • $\begingroup$ related chemistry.stackexchange.com/questions/110728/… $\endgroup$
    – Mithoron
    Nov 17, 2023 at 15:17
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    $\begingroup$ Anion barely does anything, it's the cation that can coordinate many water molecules. $\endgroup$
    – Mithoron
    Nov 17, 2023 at 15:24

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Sulfates commonly do have water of hydration, but so do many other salts such as chlorides. For instance, iron chlorides used in laboratory experiments at my job are commonly bought as $\ce{FeCl2•4H2O}$ and $\ce{FeCl3•6H2O}$.

One difference between sulfates and some other salts is the oxygen in the sulfate ion can form relatively strong hydrogen bonds with the protic hydrogen in water, enabling incorporation of additional water molecules into the crystal that aren't coordinated with the metal ion. Thus for instance magnesium ion commonly coordinates with six water molecules, but the sulfate salt commonly incorporates a seventh water molecules in its formula unit (Epsom salt) and can even have eleven at lower temperature.

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