Formulae for hydrated MgSO4 = MgSO4 5H2O
2) There are at least two reasons why heating to find percentage of water in hydrated crystals is not recommended for all hydrates. The first reason is that some hydrates have such a strong bond with the water that not all of it will be able to be removed. The second reason is that different hydrates have their own mass. Depending on the mass and type of hydrate, some of the molecule may be burned off from heating. This would lead to a false accusation that the mass loss was all from water, when in reality it could partially be the mass of the molecule.
3A) It is important to let the evaporating dish cool before measuring it for a few reasons. Besides