How to avoid errors when changing a hydrate to anhydride?

[dodgers42]

what are the possible unavoidable errors when changing a hydrate to an anhydrous. the procedure called for heating the hydrate in a crucible a few times and cooling to room temp in a desiccator until mass measured was constant. also why wouldn't this procedure work for all hydrates? thank you for help.

 

[Riogho]

This procedure is fine enough way to do it, all you are doing is evaporating the water until all of it is gone (mass doesn't change, all water is gone).

I could see it not working in the case that you have a hydrate that also has a low boiling point, and would cause it to evaporate too.

 

[C3H5N3O9]

After heating the hydrate to drive off the water, it is possible that the anhydrous would pick up water vapor from the air.
Also, there could be material (various dust particles, fingerprints, etc) on the crucible after heating it which would cause mass differences (depending on the precision of the balance.)
It is also possible that more than water is driven off when heating the crucible.
Although without viewing the actual procedure, it is hard to be certain on the sources of error.