A hydrate is a type of salt containing water within its crystal structure. In this experiment, the mass percent of water in a hydrate was determined by heating a sample of the hydrate to remove the water and then comparing the mass of the sample before and after heating. From this, the empirical formula of the hydrated salt was determined. This was carried out for copper sulfate hydrate (CuSO4*XH2O) and for magnesium chloride hydrate (MgCl2*XH2O).
A crucible was weighed to the nearest 0.001g, 5g copper sulphate hydrate (CuSo4*XH2O) was added to the crucible, and the total weight noted to the nearest 0.001g. The crucible was then heated over a Bunsen burner to evaporate the water. Once the water was evaporated, the crucible and its contents were reweighed. Calculations were performed to determine: a) the mass of the empty crucible; b) the mass of the crucible plus hydrate; and the mass of the crucible plus the pure hydrate once the water had been removed. This allowed the calculation of the mass of the pure salt recovered; the number of moles of water in the original sample; the number of moles of the pure salt in the sample; and the molar ratio of water to salt in the sample. It also allowed determination of the empirical formula for copper sulfate hydrate. The experiment was then repeated using magnesium chloride hydrate, MgCl2*XH2O.
1. The formula for the decomposition of the hydrate CuSO4*XH2O is:
CuSO4.XH2O (s) ? CuSO4 (s) + XH2O (g)
2. a) Mass of the empty crucible =53.200g
b) Mass of crucible plus hydrate =58.200g
c) Mass of the crucible plus pure salt =56.396g
3. a) Mass of water in hydrate sample =
Mass of crucible plus hydrate - mass of crucible plus pure salt = 58.200 - 56.396 =1.804g
b) Number of moles of water in sample:
Molecular weight of water = 18 g
Number of moles of water in sample
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