Question

What do water molecules disassociate in salt crystals when they are dissolved in water?

Answer 1

I am not quite sure if I follow your question. I will attempt to address what I think you are asking.

Explanation:

When `"sodium chloride, halite,"` is dissolved in water, the water solvent breaks up the solid ionic structure to give so-called `"solvated"` or `"aquated"` sodium and chloride ions:

`NaCl(s)"+ excess "H_2O(l) rarrNa^(+)(aq) + Cl^(-)(aq)`

The `Na^(+)(aq)` species is arguably `[Na(OH_2)_6]^+`, a coordination complex if you like, in which the water molecules bind to the metal centre in an ion-dipole interaction. And likewise, chloride ion is solvated. For these reasons, i.e. ionic bonds are broken, and ion-dipoles, are formed, we could classify this dissolution as an example of chemical change.