What is the percent by mass of water in cap n A sub 2 cap s times cap o sub 4 times 10 cap h sub 2 cap o ? Use percent Element is equal to total mass of element in compound over molar mass of compound times 100

In Na₂SO₄·10H₂O, the 10 water molecules contribute about 10 × 18.02 = 180.2 g per mole of compound. The molar mass of the whole hydrate is about 142.0 + 180.2 = 322.2 g/mol. Thus, the water percentage is (180.2 ÷ 322.2) × 100 ≈ 55.92%, so the answer is C, 55.92 percent.

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