Hydrated sodium sulfate has a chemical formula of Na2SO4∙ 10H2O.What is the chemical formula of the anhydrous form of the same compound?

Hydrated sodium sulfate has a chemical formula of Na₂SO₄•10H₂O. What is the chemical formula of the anhydrous form of the same compound?

The hydrated form of a compound is produced by adding water of crystallization to the anhydrous form.
Hence, the anhydrous form of the compound is Na₂SO₄.


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Update: How many water molecules are there for every Na₂SO₄?

According to the formula Na₂SO₄•10H₂O, there are 10 water molecules for every Na₂SO₄.


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A chemist starts out with 15.0 g of anydrous Na₂SO₄. If she hydrates the compound completely, how many grams of water will be added to the sample?

Molar mass of Na₂SO₄ = (23.0×2 + 32.1 + 16.0×4) g/mol = 142.1 g/mol
Molar mass of H₂O = (1.0×2 + 16.0) g/mol = 18.0 g/mol

According to the formula Na₂SO₄•10H₂O, mole ratio Na₂SO₄ : H₂O = 1 : 10
No. of moles of Na₂SO₄ present = (15.0 g) / (142.1 g/mol) = 0.1056 mol
No. of moles of H₂O added = (0.1056 mol) × 10 = 1.056 mol
Mass of H₂O added = (1.056 mol) × (18.0 g/mol) = 19.0 g