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The waters of crystallization tell us the amount of water associated with a particular molecule. Hydrated compounds have a specific number of water molecules associated with it and that number is a characteristic property of a substance. The percentage for the water of crystallization is found by taking the mass of the hydrate molecules and dividing it by the molar mass of the hydrated molecule. % = 100* mass of water molecules / mass of hydrated salt We'll use x for the mass of the water, we know the percentage, and we can find the mass of the unhydrated salt, which is 208.3 g/mol 14.8 = 100x / (208.3+x) Divide by 100 to get 0.148 = x / (208.3+x) Rearrange to solve for x 0.148(208.3+x) = x 30.8 + 0.148x = x 30.8 = 0.852x x=36.2 Since we assigned x as the mass of water, we have 36.2 g of water. In order to have a mass of water of 36 g, we need two moles of water so the formula will be BaCl2-2H2O.
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