How many water molecules were there in the hydrate?
2016-11-18 7:28 am
After the first purification step, hydrated aluminum oxide is obtained. When 100 g of this solid was heated and the water driven off, 65.36 g of Al2O3 remained.
回答 (1)
2016-11-18 10:38 am
Molar mass of Al₂O₃ = (27.0×2 + 16.0×3) g/mol = 102.0 g/mol
Molar mass of H₂O = (1.0×2 + 16.0) g/mol = 18.0 g/mol
In 100 g of the solid :
Mass of Al₂O₃ = 65.36 g
Mass of H₂O = (100 - 65.36) g = 34.64 g
In the compound :
Mole ratio Al₂O₃ : H₂O = (65.35/102.0) : (34.64/18.0) = 0.641 : 1.92 ≈ 1 : 3
In each formula unit of the hydrate, there are 3 water molecules.
Molar mass of H₂O = (1.0×2 + 16.0) g/mol = 18.0 g/mol
In 100 g of the solid :
Mass of Al₂O₃ = 65.36 g
Mass of H₂O = (100 - 65.36) g = 34.64 g
In the compound :
Mole ratio Al₂O₃ : H₂O = (65.35/102.0) : (34.64/18.0) = 0.641 : 1.92 ≈ 1 : 3
In each formula unit of the hydrate, there are 3 water molecules.
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