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. |