Question: what is the empirical formula of the hydrated salt?
Answer: Its formula is CuSO4 5H2O. The five in front of the formula for water tells us there are 5 water molecules per formula unit of CuSO4 (or 5 moles of water per mole of CuSO4). The water in the formula is referred to as the water of hydration, and the dot indicates that the water is chemically bonded to the CuSO4 salt.