A cement compound CaO.Al2O3.10H2O gives certain peaks when using the powder diffraction method. The compound now increases its water of crystallization to become CaO.Al2O3.11H2O.Will the diffraction pattern obtained be basically the same as the former, with only a slight difference, which corresponds to a slight increase in the d spacing? Or will the diffraction pattern be an entirely different pattern?

Question

It all depends upon how the water is bound. If the H2O molecules are a part of the crystalline structure, then adding an 11th H2O molecules COULD change the crystal strucure. In that case the powder diffraction pattern might be quite different. If, however, the H2O molecule just takes up more interstitial space then the pattern would have only slight differences in the d spacing. Without knowing which happens, I would make an educated guess that the latter is the case.