What is the percent by mass of water in Na2SO4⋅10⁢H2O? Use percent Element is equal to total mass of element in compound over molar mass of compound times 100

Each Na₂SO₄·10H₂O formula unit contains 10 water molecules, with a total water mass of about 10 × 18.02 = 180.2 g/mol. The full compound has a molar mass of about 142.0 + 180.2 = 322.2 g/mol. Thus, the percent by mass of water is (180.2 ÷ 322.2) × 100 ≈ 55.92%, which is choice C, 55.92 percent.

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