We tried to dissolve yttrium nitrate hydrates in ethanol and discovered that their solubility varies depending on the source, in spite of nominally the same chemical composition. Usually given as Y(NO3)3*xH2O, the compound purchased from Aldrich practically did not dissolve in absolute ethanol, whereas that from other suppliers dissolved easily at least up to 1.0 M. What could be the reason for such strange difference? Purity was 99.9% or better in all cases.
If the solids have exactly the same composition, there is no really a clear answer for that. Solubility depends on so many things... Maybe it is just a kinetic problem. Different suppliers may differ in: particle size, crystallinity (check XRD), number of hydration molecules (4, 6, etc.). Regarding crystallinity, amorphous dissolves usually better than crystalline. "Ageing" is also a variable in some particulated solids.
So... for a rigorous answer a complete characterization of the different solids shoud be performed.
SInce water would really help to dissolve nitrates, probably the difference between aldrich and the rest of suppliers is in the number of hydration molecules.
I suggest doing two XRD about the two yttrium nitrate samples to check the phase identity as well, because the same composition does not mean the presence of the same phases in the two samples. Since xH2O can mean a mixture of anhydrous and a multi-hydrated salt (e.g. x=0 and 4) and a medium hydrated salt (x=2) as well, the solubility difference can be arisen from the amount of H2O in the each phases within the yttrium nitrate samples.
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